6-Channel Intelligent Fan Controller
MAX31785
1
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
19-5703; Rev 3; 8/12
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
*EP = Exposed pad.
General Description
The MAX31785 is a closed-loop multichannel fan con-
troller. Automatic closed-loop fan control saves system
power by operating the fans at the lowest possible
speeds. Added benefits of slower fan speeds include
lower audible noise, longer fan life, and reduced system
maintenance. Based on a user-programmable lookup
table (LUT), the device automatically adjusts the speeds
of the six independent fans based on one or more of the
11 available temperature sensors. Alternately, an exter-
nal host can manually command the fan speeds and the
device automatically adjusts the fan speeds. The device
contains a fan-health-diagnostic function to help users
predict impending fan failures. The device can also
monitor up to six remote voltages.
Applications
Network Switches/Routers
Base Stations
Servers
Smart Grid Network Systems
Industrial Controls
Ordering Information
Features
S Six Independent Channels of Fan Control
Supports 3-Wire and 4-Wire Fans
Automatic Closed-Loop Fan Speed Control
RPM- or PWM-Based Control
Optional Manual Mode Control
Fast and Slow PWM Frequency Options
Staggered Fan Spin-Up Eases Power-Supply
Stress
Dual Tachometer (12-Fan Support)
Fan-Fault Detection
Fan-Health Status Meter
Nonvolatile Fan Operating Run Time Meter
S Supports Up to 11 Temperature Sensors
Up to Six External Thermal Diodes with
Automatic Series Resistance Cancellation
One Internal Temperature Sensor
Up to Four I2C Digital Temperature Sensors
Fault Detection on All Temperature Sensors
S Available 6-Channel ADC to Measure Remote
Voltages
S PMBus™-Compliant Command Interface
S I2C/SMBus-Compatible Serial Bus with Bus
Timeout Function
S On-Board Nonvolatile Fault Logging and Default
Configuration Setting
S No External Clocking Required
S +3.3V Supply Voltage
PMBus is a trademark of SMIF, Inc.
PART TEMP RANGE PIN-PACKAGE
MAX31785ETL+ -40NC to +85NC40 TQFN-EP*
MAX31785ETL+T -40NC to +85NC40 TQFN-EP*
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, go to: www.maxim-ic.com/errata.
6-Channel Intelligent Fan Controller
MAX31785
2
TABLE OF CONTENTS
Absolute Maximum Ratings ...................................................................... 6
Recommended Operating Conditions .............................................................. 6
DC Electrical Characteristics ..................................................................... 6
I2C/SMBus Interface Electrical Characteristics ....................................................... 8
I2C/SMBus Timing ............................................................................. 8
Typical Operating Characteristics ................................................................. 9
Pin Configuration ............................................................................. 10
Pin Description ............................................................................... 10
Block Diagram ............................................................................... 12
Multiple Device Connection Diagram.............................................................. 13
Detailed Description........................................................................... 14
Address Select .............................................................................16
SMBus/PMBus Operation .....................................................................16
SMBus/PMBus Communication Examples .....................................................16
Group Command ...........................................................................17
Group Command Write Format ..............................................................17
Addressing ................................................................................17
ALERT and Alert Response Address (ARA) .......................................................17
Alert Response Address (ARA) Byte Format....................................................18
Host Sends or Reads Too Few Bits .............................................................18
Host Sends or Reads Too Few Bytes ............................................................18
Host Sends Too Many Bytes or Bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Host Reads Too Many Bytes or Bits .............................................................18
Host Sends Improperly Set Read Bit in the Slave Address Byte .......................................18
Unsupported Command Code Received .........................................................18
Invalid Data Received ........................................................................18
Host Reads from a Write-Only Command ........................................................19
Host Writes to a Read-Only Command...........................................................19
SMBus Timeout.............................................................................19
PMBus Operation ...........................................................................19
PMBus Protocol Support......................................................................19
Data Format................................................................................19
Interpreting Received DIRECT Format Values .....................................................20
Sending a DIRECT Format Value ...............................................................20
Fault Management and Reporting ..............................................................21
System Watchdog Timer ......................................................................21
Temperature Sensor Operation .................................................................21
6-Channel Intelligent Fan Controller
MAX31785
3
TABLE OF CONTENTS (continued)
Fan Control Operation ......................................................................... 22
Dual Fan Applications ........................................................................22
Automatic Fan Control Operation ...............................................................22
Pulse Stretching ..........................................................................24
Fan Spin-Up ...............................................................................24
Fan Power-On Sequencing ....................................................................25
Fan Health-Meter Function ....................................................................25
PAGE (00h) ................................................................................27
CLEAR _ FAULTS (03h) .......................................................................28
WRITE_PROTECT (10h) ......................................................................28
STORE_DEFAULT_ALL (11h) ..................................................................28
RESTORE_DEFAULT_ALL (12h) ................................................................28
CAPABILITY (19h) ...........................................................................28
VOUT_MODE (20h) ..........................................................................29
VOUT_SCALE_MONITOR (2Ah) ................................................................29
FAN_CONFIG_1_2 (3Ah) .....................................................................29
FAN_COMMAND_1 (3Bh).....................................................................30
VOUT_OV_FAULT_LIMIT (40h) .................................................................30
VOUT_OV_WARN_LIMIT (42h) .................................................................30
VOUT_UV_WARN_LIMIT (43h) .................................................................31
VOUT_UV_FAULT_LIMIT (44h) .................................................................31
OT_FAULT_LIMIT (4Fh) .......................................................................31
OT_WARN_LIMIT (51h) .......................................................................31
STATUS _BYTE (78h) .........................................................................32
STATUS _WORD (79h) ........................................................................32
STATUS _VOUT (7Ah).........................................................................32
STATUS _CML (7Eh) .........................................................................33
STATUS _MFR_SPECIFIC (80h) ................................................................33
STATUS _FANS _1_ 2 (81h) .....................................................................33
READ_VOUT (8Bh) ..........................................................................34
READ_TEMPERATURE_1 (8Dh) ................................................................34
READ_FAN_SPEED_1 (90h) ...................................................................34
PMBUS_REVISION (98h) .....................................................................34
MFR_ID (99h) ..............................................................................34
MFR_MODEL (9Ah) .........................................................................34
MFR_REVISION (9Bh) .......................................................................34
MFR_LOCATION (9Ch) .......................................................................34
6-Channel Intelligent Fan Controller
MAX31785
4
TABLE OF CONTENTS (continued)
MFR_DATE (9Dh) ...........................................................................34
MFR_SERIAL (9Eh) ..........................................................................34
MFR_MODE (D1h)...........................................................................35
MFR_VOUT_PEAK (D4h) .....................................................................36
MFR_TEMPERATURE_PEAK (D6h) .............................................................36
MFR_VOUT_MIN (D7h) .......................................................................36
MFR_FAULT_RESPONSE (D9h) ................................................................36
MFR_NV_FAULT_LOG (DCh) ..................................................................37
MFR_TIME_COUNT (DDh) ....................................................................40
MFR_TEMP_SENSOR_CONFIG (F0h) ...........................................................40
MFR_FAN_CONFIG (F1h) .....................................................................41
MFR_FAN_LUT (F2h) ........................................................................43
TEMPERATURE STEP: Temperature Level Setting..................................................43
FAN SPEED STEP: Fan PWM Duty Cycle or Fan Speed Setting .......................................44
MFR_READ_FAN_PWM (F3h) .................................................................45
MFR_FAN_FAULT_LIMIT (F5h) .................................................................45
MFR_FAN_WARN_LIMIT (F6h).................................................................45
MFR_FAN_RUN_TIME (F7h)...................................................................46
MFR_FAN_PWM_AVG (F8h)...................................................................46
MFR_FAN_PWM2RPM (F9h) ..................................................................46
Applications Information........................................................................ 46
Power-Supply Decoupling.....................................................................46
Open-Drain Pins ............................................................................46
Typical Operating Circuit ....................................................................... 47
Package Information........................................................................... 47
Revision History .............................................................................. 48
Figure 1. Automatic Fan Control.................................................................. 23
Figure 2. Fan Speed Example ................................................................... 23
Figure 3. Fan Spin-Up ......................................................................... 24
Figure 4. Fan PWM to RPM Example.............................................................. 25
Figure 5. MFR_NV_FAULT_LOG ................................................................. 37
Figure 6. Fan Lookup Table (LUT) Format .......................................................... 44
LIST OF FIGURES
6-Channel Intelligent Fan Controller
MAX31785
5
Table 1. PMBus Command Codes................................................................ 14
Table 2. PMBus/SMBus Serial-Port Address ........................................................ 16
Table 3. PMBus Command Code Coefficients ...................................................... 20
Table 4. Coefficients for DIRECT Format Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Table 5. Device Parametric Monitoring States ....................................................... 21
Table 6. DS75LV Address Pin Configurations ....................................................... 21
Table 7. Fan Control Operation Modes ............................................................ 22
Table 8. Fan Health Conditions .................................................................. 26
Table 9. Page Commands ...................................................................... 27
Table 10. WRITE_PROTECT Command Byte........................................................ 28
Table 11. CAPABILITY Command Byte ............................................................ 28
Table 12. VOUT_SCALE_MONITOR .............................................................. 29
Table 13. FAN_CONFIG_1_2 Command Byte ....................................................... 29
Table 14. PWM Fan Mode (FAN_CONFIG_1_2 Bit 6 = 0) .............................................. 30
Table 15. RPM Fan Mode (FAN_CONFIG_1_2 Bit 6 = 1) .............................................. 30
Table 16. STATUS_BY TE ....................................................................... 32
Table 17. STATUS _WORD ...................................................................... 32
Table 18. STATUS_VOUT ....................................................................... 32
Table 19. STATUS _CML ........................................................................ 33
Table 20. STATUS_MFR_SPECIFIC ............................................................... 33
Table 21. STATUS_FANS_1_2 ................................................................... 33
Table 22. MFR_MODE ......................................................................... 35
Table 23. MFR_FAULT_RESPONSE............................................................... 36
Table 24. MFR_NV_FAULT_LOG ................................................................. 38
Table 25. MFR_TEMP_SENSOR_CONFIG.......................................................... 40
Table 26. MFR_FAN_CONFIG ................................................................... 41
Table 27. MFR_FAN_LUT....................................................................... 43
Table 28. Valid Temperature Range ............................................................... 43
Table 29. Monitored Fan Fault and Warning Parameters............................................... 45
Table 30. MFR_FAN_PWM2RPM................................................................. 46
LIST OF TABLES
6-Channel Intelligent Fan Controller
MAX31785
6
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
VDD to VSS ...........................................................-0.3V to +5.5V
RS- to VSS ............................................................-0.3V to +0.3V
All Other Pins Except REG18 and
REG25 Relative to VSS ........................ -0.3V to (VDD + 0.3V)*
Continuous Power Dissipation (TA = +70NC)
TQFN (derate 35.7mW/NC above +70NC)...............2857.1mW
Operating Temperature Range .......................... -40NC to +85NC
Storage Temperature Range ............................ -55NC to +125NC
Lead Temperature (soldering, 10s) ................................+300NC
Soldering Temperature (reflow) ......................................+260NC
RECOMMENDED OPERATING CONDITIONS
(TA = -40NC to +85NC.)
ABSOLUTE MAXIMUM RATINGS
DC ELECTRICAL CHARACTERISTICS
(VDD = 2.7V to 5.5V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at VDD = 3.3V, TA = +25NC, unless otherwise noted.)
*Subject to not exceeding +5.5V.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
VDD Operating Voltage Range VDD (Note 1) 2.7 5.5 V
Input Logic 1 VIH 0.7 x
VDD
VDD +
0.3 V
Input Logic 0 VIL 00.3 x
VDD V
Input Logic-High: SCL, SDA,
MSCL, MSDA VI2C_IH 2.7V P VDD P 3.6V (Note 1) 2.1 VDD +
0.3 V
Input Logic-Low: SCL, SDA,
MSCL, MSDA VI2C_IL 2.7V P VDD P 3.6V (Note 1) 0 +0.8 V
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Current ICPU (Note 2) 3mA
IPROGRAM 8
Brownout Voltage VBO Monitors VDD (Note 1) 2.40 2.46 2.55 V
Brownout Hysteresis VBOH Monitors VDD (Note 1) 30 mV
Internal System Clock fMOSC 4.0 MHz
System Clock Error (Note 3) fERR:MOSC +25NC P TA P +85NC-3 +2 %
-40NC P TA P +25NC-6.5 +1.6
Output Logic-Low VOL1 IOL = 4mA (Note 1) 0.4 V
Output Logic-High VOH1 IOH = -2mA (Note 1) VDD -
0.5 V
PWM Pullup Current IPU VPIN = VSS, VDD = 3.3V 38 55 107 FA
ADC Internal Reference 1.225 V
ADC Voltage Measurement Error VERR -1 +1 %
6-Channel Intelligent Fan Controller
MAX31785
7
DC ELECTRICAL CHARACTERISTICS (continued)
(VDD = 2.7V to 5.5V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at VDD = 3.3V, TA = +25NC, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
ADC Internal Reference
Temperature Drift -0.5 +0.5 %
ADC Internal Reference Initial
Accuracy (+25NC) -1 +1 mV
ADC Full-Scale Input Voltage VFS 1.213 1.225 1.237 V
ADC Measurement Resolution VLSB 300 FV
ADC Bit Resolution 12 Bits
RS+ Input Resistance RIN 15 MI
ADC Integral Nonlinearity INL (Note 4) Q8LSB
ADC Offset VOFFSET Q2LSB
Internal Temperature
Measurement Error TA = -40NC to +85NC-3 +3 NC
Remote Temperature
Measurement Error
(MAX31785 Error Only)
TA = 0NC to +60NC,
TDIODE = +60NC to +120NC-1.5 +1.5
NC
TA = 0NC to +60NC,
TDIODE = -45NC to +120NC-1.75 +1.75
TA = -40NC to +85NC,
TDIODE = +60NC to +120NC-2.75 +2.75
TA = -40NC to +85NC,
TDIODE = -45NC to +120NC-3.0 +3.0
Store Default All Time 45 ms
Nonvolatile Log Write Time 12 ms
Nonvolatile Log Delete Time 200 ms
Flash Endurance NFLASH TA = +50NC20,000 Write
Cycles
Data Retention TA = +50NC100 Years
Voltage Sample Rate 10 ms
RPM Sample Rate 1000 ms
Temperature Sample Rate 1000 ms
Device Startup Time Measured from POR until monitoring
begins 12 ms
Fan PWM Frequency 30 25,000 Hz
Fan PWM Resolution 7 Bits
6-Channel Intelligent Fan Controller
MAX31785
8
I2C/SMBUS INTERFACE ELECTRICAL CHARACTERISTICS
(VDD = 2.7V to 5.5V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at VDD = 3.3V, TA = +25NC, unless otherwise noted.)
Note 1: All voltages are referenced to ground (VSS). Currents entering the IC are specified as positive, and currents exiting the IC
are negative.
Note 2: This does not include pin input/output currents.
Note 3: Guaranteed by design.
Note 4: ADC has no missing codes.
Note 5: Commands MFR_MODE, STORE_DEFAULT_ALL, and RESTORE_DEFAULT_ALL require a bus-free time of 250ms.
I2C/SMBus Timing
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SCL Clock Frequency fSCL 10 100 kHz
Bus Free Time Between STOP
and START Conditions tBUF (Note 5) 1.4 ms
Hold Time (Repeated) START
Condition tHD:STA 4.0 Fs
Low Period of SCL tLOW 4.7 Fs
High Period of SCL tHIGH 4.0 Fs
Data Hold Time tHD:DAT Receive 0 ns
Transmit 300
Data Setup Time tSU:DAT 100 ns
START Setup Time tSU:STA 4.7 Fs
SDA and SCL Rise Time tR300 ns
SDA and SCL Fall Time tF300 ns
STOP Setup Time tSU:STO 4.0 Fs
Clock Low Timeout tTO 25 35 ms
SCL
NOTE: TIMING IS REFERENCED TO VIL(MAX) AND VIH(MIN).
SDA
STOP START REPEATED
START
tBUF
tHD:STA
tHD:DAT tSU:DAT
tSU:STO
tHD:STA tSP
tSU:STA
tHIGH
tR
tF
tLOW
6-Channel Intelligent Fan Controller
MAX31785
9
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
FAN POWER-ON SEQUENCING
MAX31785 toc05
100ms/div
0V
0V
0V
0V
5V/div
PWM2
PWM1
PWM0
CONTROL
IDD vs. TIME DURING A NONVOLATILE LOG WRITE
(TA = +25°C, VDD = 3.3V)
MAX31785 toc04
2ms/div
0mA
1mA/div
WEAK PULLUP VOLTAGE
vs. TIME DURING POWER-UP
MAX31785 toc03
2ms/div
0V
VDD
PWMO
0V
NO LOAD
CONNECTED
TO PWM
2V/div
SUPPLY CURRENT vs. TEMPERATURE
(VDD = 3.3V, NO PWM SWITCHING)
MAX31785 toc02
TEMPERATURE (°C)
IDD (mA)
806020 400-20
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
2.0
-40 100
SUPPLY CURRENT vs. SUPPLY VOLTAGE
(NO PWM SWITCHING)
MAX31785 toc01
VDD (V)
IDD (mA)
5.14.73.9 4.33.53.1
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
2.0
2.7 5.5
6-Channel Intelligent Fan Controller
MAX31785
10
Pin Description
Pin Configuration
PIN NAME FUNCTION
1 RS-4 Ground Reference for Thermal Diode or Remote Voltage ADC4 Measurement
2, 21, 36 VSS Digital-Supply Return Node (Ground)
3 RS+4 Thermal Diode or Remote Voltage ADC Input, Measurement Relative to RS-4
4 RS-3 Ground Reference for Thermal Diode or Remote Voltage ADC3 Measurement
5 RS+3 Thermal Diode or Remote Voltage ADC Input, Measurement Relative to RS-3
6 RS+0 Thermal Diode or Remote Voltage ADC Input, Measurement Relative to RS-0
7 RS-0 Ground Reference for Thermal Diode or Remote Voltage ADC0 Measurement
8 RS+1 Thermal Diode or Remote Voltage ADC Input, Measurement Relative to RS-1
9 VDD Supply Voltage. Bypass VDD to VSS with a 0.1FF capacitor.
10 RS-1 Ground Reference for Thermal Diode or Remote Voltage ADC1 Measurement
11 RS+2 Thermal Diode or Remote Voltage ADC Input, Measurement Relative to RS-2
12 RS-2 Ground Reference for Thermal Diode or Remote Voltage ADC2 Measurement
13 RST Reset Active-Low Input
14 MSDA Master I2C Data Input/Output. Open-drain output.
15 MSCL Master I2C Clock Input/Output. Open-drain output.
16 PWM5 Fan PWM Output #5. CMOS push-pull output. Low when the fan is disabled. A 100% duty cycle
implies this pin is continuously high.
17 TACH5 Fan Tachometer Input
18 PWM4 Fan PWM Output #4. CMOS push-pull output. Low when the fan is disabled. A 100% duty cycle
implies this pin is continuously high.
19 TACH4 Fan Tachometer Input
TOP VIEW
35
36
34
33
12
11
13
VSS
RS-3
RS+3
RS+0
RS-0
14
RS-4
TACH1
TACH2
PWM2
PWM0
REG25
TACH0
TACH3
REG18
12 4567
27282930 26 24 23 22
CONTROL
VSS
PWM4
TACH5
PWM5
MSCL
RS+4
PWM1
3
25
37
A1/TACHSEL MSDA
38
39
40
RS-5
RS+5
RS-2
RS+2
EP
A0
32
15
TACH4
SCL
31
16
17
18
19
20 PWM3
RS+1
VDD
RS-1 VSS
8910
21
SDA
FAULT
ALERT RST
+
TQFN
(6mm × 6mm × 0.75mm)
MAX31785
6-Channel Intelligent Fan Controller
MAX31785
11
Pin Description (continued)
Note: All pins except VDD, VSS, REG18, REG25, ADC, and the EP are high impedance with a 50µA pullup during device power-up
and reset. After device reset, the weak pullup is removed, and the pin is configured as input or output.
PIN NAME FUNCTION
20 PWM3 Fan PWM Output #3. CMOS push-pull output. Low when the fan is disabled. A 100% duty cycle
implies this pin is continuously high.
22 REG18 Regulator for Low-Voltage Digital Circuitry. Bypass REG18 to VSS with 1FF and 10nF capacitors. Do
not connect other circuitry to this pin.
23 TACH3 Fan Tachometer Input
24 PWM2 Fan PWM Output #2. CMOS push-pull output. Low when the fan is disabled. A 100% duty cycle
implies this pin is continuously high.
25 TACH2 Fan Tachometer Input
26 PWM1 Fan PWM Output #1. CMOS push-pull output. Low when the fan is disabled. A 100% duty cycle
implies this pin is continuously high.
27 TACH1 Fan Tachometer Input
28 PWM0 Fan PWM Output #0. CMOS push-pull output. Low when the fan is disabled. A 100% duty cycle
implies this pin is continuously high.
29 REG25 Regulator for Analog Circuitry. Bypass REG25 to VSS with 1FF and 10nF capacitors. Do not connect
other circuitry to this pin.
30 TACH0 Fan Tachometer Input
31 SDA I2C/SMBus-Compatible Input/Output
32 SCL I2C/SMBus-Compatible Clock Input
33 A0 SMBus Address 0 Input. This pin is sampled on device power-up to determine the SMBus address;
connect a 100kI resistor from this pin to either VSS or VDD to set the address.
34 FAULT
Active-Low, Open-Drain Fault Input/Output. If enabled with the MFR_FAULT_RESPONSE command, this
pin is asserted during a fault condition (fan speed, overtemperature, overvoltage, or undervoltage). Also,
if enabled with the MFR_FAULT_RESPONSE command, this pin is monitored and when it is asserted the
fans can be configured to be forced to 100% PWM duty cycle. This pin is used to provide hardware fault
control across multiple devices. This output is unconditionally deasserted when RST is asserted or the
device is power cycled. This pin has a 50Fs deglitch filter.
35 CONTROL
Global Fan-Off Control. When this pin is connected low, all fans are forced off (other functionality
remains active). When this pin is connected high (or left open circuit), fans operate normally. This pin
has a 50Fs deglitch filter and contains a weak pullup.
37 A1/
TACHSEL
SMBus Address 1 Input/Dual Tach-Select Output. This dual-function pin is sampled on device
power-up to determine the SMBus address; connect a 100kI resistor from this pin to either VSS or
VDD to set the address. After device power-up, this pin becomes an output that selects between two
tachometers in dual-fan applications.
38 ALERT Active-Low, Open-Drain Alert Output
39 RS-5 Ground Reference for Thermal Diode or Remote Voltage ADC5 Measurement
40 RS+5 Thermal Diode or Remote Voltage ADC Input, Measurement Relative to RS-5
— EP Exposed Pad (Bottom Side of Package). Connect EP to VSS.
6-Channel Intelligent Fan Controller
MAX31785
12
Block Diagram
MAXQ is a registered trademark of Maxim Integrated
Products, Inc.
ADC
TEMP
SENSOR
FLASHRAM
A1/TACHSEL
A0
MUX
MSDA
VSS
VSS
VSS
VDD
REG18
REG25
MSCL
SDA
SCL
ALERT
RST
POWER
CONTROL
2.5V
VREG
1.8V
VREG
4MHz
OSCILLATOR
SMBus
MASTER
INTERFACE
SMBus
SLAVE
INTERFACE
16-BIT
MAXQ®
RISC CORE
SYSTEM
CONTROL
SIGNALS
PULSE-
WIDTH
MODULATOR
PWM0
PWM1
PWM2
PWM3
PWM4
PWM5
FAN
TACHOMETER
INPUTS
CONTROL
RS+0
RS-0
RS+1
RS-1
RS+2
RS-2
RS+3
RS-3
RS+4
RS-4
RS+5
RS-5
TACH0
TACH1
TACH2
TACH3
TACH4
TACH5
FAULT
MAX31785
6-Channel Intelligent Fan Controller
MAX31785
13
Multiple Device Connection Diagram
SDA
SCL
RST
ALERT
ALERT
FAULT
CONTROL
A1/TACHSEL
A0
SDA
SCL
RST
ALERT
FAULT
CONTROL
A1/TACHSEL
A0
ADDITIONAL DEVICES
CONTROL
DATA
CLOCK
RST
HOST
INTERFACE
+3.3V
+3.3V
MAX31785
#0
MAX31785
#1
6-Channel Intelligent Fan Controller
MAX31785
14
Table 1. PMBus Command Codes
Detailed Description
The MAX31785 is a closed-loop fan controller. Automatic
closed-loop fan control saves system power by operat-
ing the fans at the lowest possible speeds. Added ben-
efits of slower fan speeds include lower audible noise,
longer fan life, and reduced system maintenance. Based
on a user-programmable lookup table (LUT), the device
automatically adjust the speeds of the six independent
fans based on one or more of the 11 available tem-
perature sensors. Temperature offset can be added to
individual sensors to compensate for thermal differences
in a system. Alternately, an external host can manually
command the fan speeds and the device automatically
adjusts the fan speeds. The device can also monitor up
to six remote voltages.
The device provides ALERT and FAULT output sig-
nals. Host communications are conducted through a
PMBusK-compatible communications port. Address
input connections are also provided to allow up to four
MAX31785 devices to reside on the system’s I/O bus.
PMBus is a trademark of SMIF, Inc.
CODE COMMAND NAME TYPE
PAGE
0–5
PAGE
6–16
PAGE
17–22
PAGE
255 NO. OF
BYTES
FLASH
STORED
(NOTE 2)
DEFAULT
VALUE
(NOTE 2)
(NOTE 1)
00h PAGE R/W Byte R/W R/W R/W R/W 1 N 00h
03h CLEAR_FAULTS Send Byte W W W W 0 N —
10h WRITE_PROTECT R/W Byte R/W R/W R/W R/W 1 N 00h
11h STORE_DEFAULT_ALL Send Byte W W W W 0 N —
12h RESTORE_DEFAULT_ALL Send Byte W W W W 0 N —
19h CAPABILITY Read Byte R R R R 1 N 00h/10h
20h VOUT_MODE Read Byte R R R R 1 FIXED 40h
2Ah VOUT_SCALE_MONITOR R/W Word — — R/W — 2 Y 7FFFh
3Ah FAN_CONFIG_1_2 R/W Byte R/W — — — 1 Y 00h
3Bh FAN_COMMAND_1 R/W Word R/W — — — 2 Y FFFFh
40h VOUT_OV_FAULT_LIMIT R/W Word — — R/W — 2 Y 7FFFh
42h VOUT_OV_WARN_LIMIT R/W Word —— R/W — 2 Y 7FFFh
43h VOUT_UV_WARN_LIMIT R/W Word — — R/W — 2 Y 0000h
44h VOUT_UV_FAULT_LIMIT R/W Word — — R/W — 2 Y 0000h
4Fh OT_FAULT_LIMIT R/W Word — R/W — — 2 Y 7FFFh
51h OT_WARN_LIMIT R/W Word — R/W — — 2 Y 7FFFh
78h STATUS_BYTE Read Byte R R R R 1 N 00h
79h STATUS_WORD Read Word R R R R 2 N 0000h
7Ah STATUS_VOUT Read Byte — — R — 1 N 00h
7Eh STATUS_CML Read Byte R R R R 1 N 00h
80h STATUS_MFR_SPECIFIC Read Byte — R — — 1 N 00h
81h STATUS_FANS_1_2 Read Byte R — — — 1 N 00h
8Bh READ_VOUT Read Word — — R — 2 N 0000h
8Dh READ_TEMPERATURE_1 Read Word — R — — 2 N 0000h
90h READ_FAN_SPEED_1 Read Word R — — — 2 N 0000h
98h PMBUS_REVISION Read Byte R R R R 1 FIXED 11h
99h MFR_ID Read Byte R R R R 1 FIXED 4Dh
9Ah MFR_MODEL Read Byte R R R R 1 FIXED 53h
9Bh MFR_REVISION Read Word R R R R 2 FIXED 3030h
9Ch MFR_LOCATION Block R/W R/W R/W R/W R/W 8 Y (Note 3)
6-Channel Intelligent Fan Controller
MAX31785
15
Table 1. PMBus Command Codes (continued)
Note 1: Common commands are shaded. Access through any page results in the same device response.
Note 2: In the Flash Stored column, an “N” indicates that this parameter is not stored in flash memory when the STORE_
DEFAULT_ALL command is executed and the value shown in the Default Value column is automatically loaded upon
power-on reset or when the RST pin is asserted. A “Y” in the Flash Stored column indicates that the currently loaded
value in this parameter is stored in flash memory when the STORE_DEFAULT_ALL command is executed and is automati-
cally loaded upon power-on reset or when the RST pin is asserted and the value shown in the Default Value column is
the value when shipped from the factory. “FIXED” in the Flash Stored column means this value is fixed at the factory and
cannot be changed.
Note 3: The factory-set default value for this 8-byte block is 3130313031303130h.
Note 4: The factory-set default value for the complete block of the MFR_NV_FAULT_LOG is FFh.
Note 5: The factory-set default value for the complete block is 00h.
CODE COMMAND NAME TYPE
PAGE
0–5
PAGE
6–16
PAGE
17–22
PAGE
255 NO. OF
BYTES
FLASH
STORED
(NOTE 2)
DEFAULT
VALUE
(NOTE 2)
(NOTE 1)
9Dh MFR_DATE Block R/W R/W R/W R/W R/W 8 Y (Note 3)
9Eh MFR_SERIAL Block R/W R/W R/W R/W R/W 8 Y (Note 3)
D1h MFR_MODE R/W Word R/W R/W R/W R/W 2 Y 0000h
D4h MFR_VOUT_PEAK R/W Word — — R/W — 2 N 0000h
D6h MFR_TEMPERATURE_PEAK R/W Word — R/W — — 2 N 8000h
D7h MFR_VOUT_MIN R/W Word — — R/W — 2 N 7FFFh
D9h MFR_FAULT_RESPONSE R/W Byte R/W R/W R/W — 1 Y 00h
DCh MFR_NV_FAULT_LOG Block Read R R R R 255 Y (Note 4)
DDh MFR_TIME_COUNT Block R/W R/W R/W R/W R/W 4 N (Note 5)
F0h MFR_TEMP_SENSOR_CONFIG R/W Word — R/W — — 2 Y 0000h
F1h MFR_FAN_CONFIG R/W Word R/W — — — 2 Y 0000h
F2h MFR_FAN_LUT Block R/W R/W — — — 32 Y (Note 5)
F3h MFR_READ_FAN_PWM Read Word R — — — 2 N 0000h
F5h MFR_FAN_FAULT_LIMIT R/W Word R/W — — — 2 Y 0000h
F6h MFR_FAN_WARN_LIMIT R/W Word R/W — — — 2 Y 0000h
F7h MFR_FAN_RUN_TIME R/W Word R/W — — — 2 Y 0000h
F8h MFR_FAN_PWM_AVG R/W Word R/W — — — 2 Y 0000h
F9h MFR_FAN_PWM2RPM Block R/W R/W — — — 8 Y (Note 5)
6-Channel Intelligent Fan Controller
MAX31785
16
Address Select
On device power-up, the device samples the A0 and A1
pins to determine the PMBus/SMBus serial-port address.
SMBus/PMBus Operation
The device implements the PMBus command structure
using the SMBus format. The structure of the data flow
between the host and the slave is shown below for sev-
eral different types of transactions. Data is sent most
significant bit (MSB) first.
Table 2. PMBus/SMBus Serial-Port
Address
SMBus/PMBus Communication Examples
KEY:
S = START
Sr = REPEATED START
P = STOP
W = WRITE BIT (0)
R = READ BIT (1)
A = ACKNOWLEDGE (0)
NA = NOT ACKNOWLEDGE (1)
SHADED BLOCK = SLAVE TRANSACTION
READ WORD FORMAT
1 7 1 1 8 1 1 7 1 1 8 1 8 1 1
SSLAVE
ADDRESS W A COMMAND
CODE A Sr SLAVE
ADDRESS R A DATA BYTE
LOW ADATA BYTE
HIGH NA P
READ BYTE FORMAT
1 7 1 1 8 1 1 7 1 1 8 1 1
SSLAVE
ADDRESS W A COMMAND
CODE A Sr SLAVE
ADDRESS R A DATA BYTE NA P
WRITE WORD FORMAT
1 7 1 1 8 1 8 1 8 1 1
SSLAVE
ADDRESS W A COMMAND
CODE ADATA BYTE
LOW ADATA BYTE
HIGH A P
WRITE BYTE FORMAT
1 7 1 1 8 1 8 1 1
SSLAVE
ADDRESS W A COMMAND
CODE ADATA BYTE A P
SEND BYTE FORMAT
1 7 1 1 8 1 1
SSLAVE
ADDRESS W A COMMAND
CODE A P
A1 A0 7-BIT SLAVE
ADDRESS
100kI to VSS 100kI to VSS 1010 010 (A4h)
100kI to VDD 1010 011 (A6h)
100kI to VDD 100kI to VSS 1010 100 (A8h)
100kI to VDD 1010 101 (AAh)
6-Channel Intelligent Fan Controller
MAX31785
17
Group Command
The device supports the group command. With the
group command, a host can write different data to
multiple devices on the same serial bus with one long
continuous data stream. All the devices addressed dur-
ing this transaction wait for the host to issue a STOP
before beginning to respond to the command.
KEY:
S = START
Sr = REPEATED START
P = STOP
W = WRITE BIT (0)
A = ACKNOWLEDGE (0)
SHADED BLOCK = SLAVE TRANSACTION
Group Command Write Format
Addressing
The device responds to receiving its fixed slave address
by asserting an acknowledge (ACK) on the bus. The
device does not respond to a general call address; it
only responds when it receives its fixed slave address.
The only exception to this operation is if the ALERT
output is enabled (ALERT bit = 1 in MFR_MODE) and
ALERT has been asserted. When this condition occurs,
the device only recognizes the alert response address
(0001 100, 18h). See the ALERT and Alert Response
Address (ARA) section for more details.
ALERT and Alert Response Address (ARA)
If the ALERT output is enabled (ALERT bit = 1 in
MFR_MODE), when a fault occurs the device asserts the
ALERT signal and then waits for the host to send the alert
response address (ARA) as shown in the Alert Response
Address (ARA) Byte Format section. While waiting for
the ARA, the device does not respond to its fixed
slave address.
When the ARA is received and the device is asserting
ALERT, the device ACKs it and then attempts to place
its fixed slave address on the bus by arbitrating the
bus, since another device could also try to respond to
the ARA. The rules of arbitration state that the lowest
address device wins. If the device wins the arbitration,
it deasserts ALERT and begins to respond to its fixed
slave address. If the device loses arbitration, it keeps
ALERT asserted and waits for the host to once again
send the ARA.
SLAVE ADDRESS, COMMAND BYTE, AND DATA WORD FOR DEVICE 1
1 7 1 1 8 1 8 1 8 1
SSLAVE
ADDRESS W A COMMAND
CODE ADATA BYTE
LOW ADATA BYTE
HIGH AU U U
SLAVE ADDRESS, COMMAND BYTE, AND DATA BYTE FOR DEVICE 2
1 7 1 1 8 1 8 1
Sr SLAVE
ADDRESS W A COMMAND
CODE ADATA BYTE AU U U
SLAVE ADDRESS AND SEND BYTE FOR DEVICE 3
1 7 1 1 8 1
Sr SLAVE
ADDRESS W A COMMAND
CODE AU U U
U U U
SLAVE ADDRESS, COMMAND BYTE, AND DATA WORD FOR DEVICE N
1 7 1 1 8 1 8 1 8 1 1
Sr SLAVE
ADDRESS W A COMMAND
CODE ADATA BYTE
LOW ADATA BYTE
HIGH A P
6-Channel Intelligent Fan Controller
MAX31785
18
Host Sends or Reads Too Few Bits
If for any reason the host does not complete writing a full
byte or reading a full byte from the device before a START
or STOP is received, the device does the following:
1) Ignores the command.
2) Sets the CML bit in STATUS_BYTE.
3) Sets the CML bit in STATUS_WORD.
4) Sets the DATA_FAULT bit in STATUS_CML.
5) Notifies the host through ALERT assertion (if enabled).
Host Sends or Reads Too Few Bytes
For each supported command, the device expects a
fixed number of bytes to be written or read from the
device. If for any reason fewer than the expected number
of bytes is written to or read from the device, the device
completely ignores the command and takes no action.
Host Sends Too Many Bytes or Bits
For each supported command, the device expects a
fixed number of bytes to be written to the device. If for
any reason more than the expected number of bytes or
bits is written to the device, the device does the following:
1) Ignores the command.
2) Sets the CML bit in STATUS_BYTE.
3) Sets the CML bit in STATUS_WORD.
4) Sets the DATA_FAULT bit in STATUS_CML.
5) Notifies the host through ALERT assertion (if enabled).
Host Reads Too Many Bytes or Bits
For each supported command, the device expects a fixed
number of bytes to be read from the device. If for any
reason more than the expected number of bytes or bits is
read from the device, the device does the following:
1) Sends all ones (FFh) as long as the host keeps
acknowledging.
2) Sets the CML bit in STATUS_BYTE.
3) Sets the CML bit in STATUS_WORD.
4) Sets the DATA_FAULT bit in STATUS_CML.
5) Notifies the host through ALERT assertion (if enabled).
Host Sends Improperly Set Read Bit
in the Slave Address Byte
If the device receives the R/W bit in the slave address
set to one immediately preceding the command code,
the device does the following (note this does not apply
to ARA):
1) ACKs the address byte.
2) Sends all ones (FFh) as long as the host keeps
acknowledging.
3) Sets the CML bit in STATUS_BYTE.
4) Sets the CML bit in STATUS_WORD.
5) Sets the DATA_FAULT bit in STATUS_CML.
6) Notifies the host through ALERT assertion (if enabled).
Unsupported Command Code Received
If the host sends the device a command code that it
does not support, or if the host sends a command code
that is not supported by the current PAGE setting, the
device does the following:
1) Ignores the command.
2) Sets the CML bit in STATUS_BYTE.
3) Sets the CML bit in STATUS_WORD.
4) Sets the COMM_FAULT bit in STATUS_CML.
5) Notifies the host through ALERT assertion (if enabled).
Invalid Data Received
The device checks the PAGE and WRITE_PROTECT
command codes for valid data. If the host writes a data
value that is invalid, the device does the following:
1) Ignores the command.
2) Sets the CML bit in STATUS_BYTE.
3) Sets the CML bit in STATUS_WORD.
4) Sets the DATA_FAULT bit in STATUS_CML.
5) Notifies the host through ALERT assertion (if enabled).
Alert Response Address (ARA) Byte Format
1 7 1 1 8 1 1
SARA
0001100 R A DEVICE SLAVE ADDRESS
WITH LSB = 0 NA P
6-Channel Intelligent Fan Controller
MAX31785
19
Host Reads from a Write-Only Command
When a read request is issued to a write-only
command (CLEAR_FAULTS, STORE_DEFAULT_ALL,
RESTORE_DEFAULT_ALL), the device does the following:
1) ACKs the address byte.
2) Ignores the command.
3) Sends all ones (FFh) as long as the host keeps
acknowledging.
4) Sets the CML bit in STATUS_BYTE.
5) Sets the CML bit in STATUS_WORD.
6) Sets the DATA_FAULT bit in STATUS_CML.
7) Notifies the host through ALERT assertion (if enabled).
Host Writes to a Read-Only Command
When a write request is issued to a read-only command,
the device does the following:
1) Ignores the command.
2) Sets the CML bit in STATUS_BYTE.
3) Sets the CML bit in STATUS_WORD.
4) Sets the COMM_FAULT bit in STATUS_CML.
5) Notifies the host through ALERT assertion (if enabled).
SMBus Timeout
If during an active SMBus communication sequence
the SCL signal is held low for greater than the timeout
duration (tTO), the device terminates the sequence and
resets the serial bus. It takes no other action. No status
bits are set.
PMBus Operation
From a software perspective, the device appears as a
PMBus device capable of executing a subset of PMBus
commands. A PMBus 1.1-compliant device uses the
SMBus version 1.1 for transport protocol and responds
to the SMBus slave address. In this data sheet, the term
SMBus is used to refer to the electrical characteristics
of the PMBus communication using the SMBus physi-
cal layer. The term PMBus is used to refer to the PMBus
command protocol. The device employs a number of
standard SMBus protocols to program output voltage
and warning/faults thresholds, read monitored data, and
provide access to all manufacturer-specific commands.
The device supports the group command. The group
command is used to send commands to more than one
PMBus device. It is not required that all the devices
receive the same command. However, no more than
one command can be sent to any one device in one
group command packet. The group command must not
be used with commands that require receiving devices
to respond with data, such as the STATUS_BYTE com-
mand. When the device receives a command through
this protocol, it immediately begins execution of the
received command after detecting the STOP condition.
The device supports the PAGE command and uses it to
select which individual channel to access. When a data
word is transmitted, the lower order byte is sent first and
the higher order byte is sent last. Within any byte, the
most significant bit (MSB) is sent first and the least sig-
nificant bit (LSB) is sent last.
PMBus Protocol Support
The device supports a subset of the commands defined
in the PMBus™ Power System Management Protocol
Specification Part II - Command Language, Revision 1.1.
For detailed specifications and the complete list of
PMBus commands, refer to Part II of the PMBus spec-
ification available at www.PMBus.org. The support-
ed PMBus commands and the corresponding device
behavior are described in this document. All data values
are represented in DIRECT format, unless otherwise
stated. Whenever the PMBus specification refers to the
PMBus device, it is referring to the MAX31785 operat-
ing in conjunction with a fan. While the command can
call for turning on or turning off the PMBus device, the
MAX31785 always remains on to continue communicat-
ing with the PMBus master, and the MAX31785 transfers
the command to the fan accordingly.
Data Format
Voltage data for commanding or reading the output
voltage or related parameters (such as the overvolt-
age threshold) is presented in DIRECT format. DIRECT
format data is a 2-byte, two’s complement binary value.
DIRECT format data can be used with any command that
sends or reads a parametric value. The DIRECT format
uses an equation and defined coefficients to calculate
the desired values. Table 3 shows the coefficients used
by the device.
6-Channel Intelligent Fan Controller
MAX31785
20
Interpreting Received
DIRECT Format Values
The host system uses the following equation to convert
the value received from the PMBus device—in this case,
the MAX31785—into a reading of volts, degrees Celsius,
or other units as appropriate:
X = (1/m) x (Y x 10-R - b)
where X is the calculated, real world value in the appro-
priate units (V, NC, etc.); m is the slope coefficient; Y is
the 2-byte, two’s complement integer received from the
PMBus device; b is the offset; and R is the exponent.
Sending a DIRECT Format Value
To send a value, the host must use the below equation
to solve for Y:
Y = (mX + b) x 10R
where Y is the 2-byte, two’s complement integer to be
sent to the unit; m is the slope coefficient; X is the real
world value, in units such as volts, to be converted for
transmission; b is the offset; and R is the exponent.
The following example demonstrates how the host can
send and retrieve values from the device. Table 4 shows
the coefficients used in the following parameters.
If the host received a value of 0D89h on a READ_VOUT
command, this is equivalent to:
X = (1/1) x (0D89h x 10-(-0) - 0) = 3465mV = 3.465V
All voltage-related parameters of PMBus devices are
reported as positive values. It is up to the system to know
that a particular output is negative if that is of interest to
the system. All output voltage-related commands use 2
data bytes.
Table 3. PMBus Command Code Coefficients
Table 4. Coefficients for DIRECT Format
Value
PARAMETER COMMANDS UNITS RESOLUTION MAX m b R
Voltage
VOUT_OV_FAULT_LIMIT
VOUT_OV_WARN_LIMIT
VOUT_UV_WARN_LIMIT
VOUT_UV_FAULT_LIMIT
READ_VOUT
MFR_VOUT_PEAK
MFR_VOUT_MIN
mV 1 32,767 1 0 0
Voltage Scaling VOUT_SCALE_MONITOR — 1/32,767 1 32,767 0 0
Temperature
OT_FAULT_LIMIT
OT_WARN_LIMIT
READ_TEMPERATURE_1
MFR_TEMPERATURE_PEAK
NC0.01 327.67 1 0 2
Fan Speed
READ_FAN_SPEED_1
FAN_COMMAND_1
MFR_FAN_FAULT_LIMIT
MFR_FAN_WARN_LIMIT
RPM 1 32,767 1 0 0
FAN_COMMAND_1
MFR_READ_FAN_PWM
MFR_FAN_FAULT_LIMIT
MFR_FAN_WARN_LIMIT
MFR_FAN_PWM_AVG
% 0.01 327.67 1 0 2
COMMAND
CODE COMMAND NAME m b R
8Bh READ_VOUT 100
6-Channel Intelligent Fan Controller
MAX31785
21
Fault Management and Reporting
For reporting faults/warnings to the host on a real-time
basis, the device asserts the open-drain ALERT pin (if
enabled in MFR_MODE) and sets the appropriate bit in
the various status registers. On recognition of the ALERT
assertion, the host or system manager is expected to poll
the I2C bus to determine the device asserting ALERT.
The host sends the SMBus ARA (0001 100). The device
ACKs the SMBus ARA, transmits its slave address, and
deasserts ALERT. The system controller then communi-
cates with PMBus commands to retrieve the fault/warn-
ing status information from the device.
See the individual command sections for more details.
Faults and warnings that are latched in the status regis-
ters are cleared when any one of the following conditions
occurs:
• ACLEAR_FAULTScommandisreceived.
• TheRST pin is toggled.
• Biaspowertothedeviceisremovedandthenreapplied.
The device responds to fault conditions accord-
ing to the manufacturer fault response command
(MFR_FAULT_RESPONSE). This command byte
determines how the device should respond to each
particular fault. Table 5 illustrates the required con-
ditions and fault actions for specific parameters.
System Watchdog Timer
The device uses an internal watchdog timer that is inter-
nally reset every 10ms. In the event that the device is
locked up and this watchdog reset does not occur after
500ms, the device automatically resets. After the reset
occurs, the device reloads all configuration values that
were stored to flash and begins normal operation. After
the reset, the device also does the following:
1) Sets the NONE OF THE ABOVE bit in STATUS_BYTE.
2) Sets the NONE OF THE ABOVE and MFR bits in
STATUS_WORD.
3) Sets the WATCHDOG bit in STATUS_MFR_SPECIFIC.
4) Notifies the host through ALERT assertion (if enabled
in MFR_MODE).
Temperature Sensor Operation
The device can monitor up to 11 different temperature
sensors. It can monitor up to four remote I2C-based
temperature sensors plus six remote diodes and its own
internal temperature sensor. Each of the enabled temper-
ature sensors is measured once a second. The remote
diode and internal temperature sensors are averaged
eight times to reduce the affect of noise. Each time the
device attempts to read a temperature sensor it checks
for faults. For the remote diode, a fault is defined as
reading greater than +160NC or less than -60NC. For the
internal temperature sensor, a fault is defined as reading
greater than +130NC or less than -60NC. For the I2C tem-
perature sensors, a fault is defined as a communication
access failure. Temperature sensor faults are reported by
setting the temperature reading to 7FFFh. A temperature
sensor fault results in the setting of the TEMPERATURE
bit in STATUS_BYTE and STATUS_WORD and ALERT is
asserted (if enabled in MFR_MODE). No bits are set in
STATUS_MFR_SPECIFIC.
The temperatures do not have to be used to control the
fan speed. They can be enabled and used for tempera-
ture monitoring only. Reading disabled temperature sen-
sors returns a fixed value of 0000h.
The remote diode temperature sensor can support either
npn or pnp transistors. The device automatically cancels
the series resistance that can affect remote diodes that
are located far from the device.
The device can control up to four DS75LV digital temper-
ature sensors. The A0, A1, and A2 pins on the DS75LV
should be configured as shown in Table 6. The thermo-
stat function on the DS75LV is not used and thus the O.S.
output should be left open circuit.
Table 5. Device Parametric Monitoring States
Table 6. DS75LV Address Pin Configurations
PARAMETER REQUIRED CONDITIONS FOR ACTIVE MONITORING ACTION DURING A FAULT
Overvoltage Voltage Monitoring Enabled (ADC_ENABLE in MFR_MODE = 1) Continue Monitoring
Undervoltage Voltage Monitoring Enabled (ADC_ENABLE in MFR_MODE = 1) Continue Monitoring
Overtemperature Temp Sensor Enabled (ENABLE in MFR_TEMP_SENSOR_CONFIG = 1) Continue Monitoring
Fan Speed Fan Enabled (Bit 7 in FAN_CONFIG_1_2 = 1) Continue Monitoring
PAGE MAX31785 I2C
TEMP SENSOR
DS75LV ADDRESS PIN
CONFIGURATION
A2 A1 A0
13 TEMP SENSOR I2C 0 0 0 0
14 TEMP SENSOR I2C 1 0 0 1
15 TEMP SENSOR I2C 2 0 1 0
16 TEMP SENSOR I2C 3 0 1 1
6-Channel Intelligent Fan Controller
MAX31785
22
Fan Control Operation
Fan control has four operational modes. The mode is
determined by the combination of FAN_COMMAND_1
and bit 6 of FAN_CONFIG_1_2 (see Table 7). Fan control
can be disabled by setting bit 7 in FAN_CONFIG_1_2 to
zero.
Dual Fan Applications
In dual fan applications operating in RPM mode, the
tachometer selected when TACHSEL = 0 is close-
loop-controlled to the target RPM. Once PWM ramp-
ing is complete, TACHSEL toggles between the two
tachometers every 500ms for monitoring purposes. The
slower of the two tachometer signals is reported by
READ_FAN_SPEED_1 and is used as a comparison for
fan faults and warning. If one of the two tachometer sig-
nals operate at a slower speed, it is recommended that
the slower tachometer be presented to the TACH input
when TACHSEL = 0. If more than one fan channel is
configured for dual fan operation, these fans must com-
plete ramping to the target fan speed before the device
begins to toggle the TACHSEL output and monitor both
tachometers.
Automatic Fan Control Operation
In the automatic mode, the fan is controlled in a closed
loop based on the controlling temperature (the highest
postnormalized temperature reading) and the associ-
ated fan control PWM duty cycle (in %) or fan speed
(in RPM). These parameters are assigned in the fan
lookup table (LUT). See the MFR_FAN_LUT description
for configuration details. When a controlling temperature
exceeds the temperature level programmed in the LUT,
the device outputs a PWM duty cycle or adjusts the fan
speed associated with that temperature. See Figure 1 for
an example.
One or all of the 11 available temperature sensors can
be used to control the fan speed. Each temperature
sensor has an offset adjustment that allows monitoring
specific temperature zones with different thermal char-
acteristics. In Figure 1, remote diode temperature sensor
0 is monitoring a zone that is 15NC more sensitive than
the zone that the I2C temperature sensor 3 is measuring.
To keep the audible noise and fan power consumption
as low as possible, the device allows each temperature
sensor to have a temperature offset added. This allows
temperature zones with different thermal profiles to con-
trol the fan at the lowest possible speed to maintain the
required temperature.
If no temperature sensors are assigned to control the fan,
the output fan PWM signal is ramped to 100% duty cycle.
In Figure 2, at temperature sample 1, the required fan
speed is at the level associated with temperature level
2 and since temperature sample 1 is above temperature
level 3, the fan PWM duty cycle needs to be increased
to increase the fan speed. The device increases the fan
PWM duty cycle at a rate controlled by the RAMP bits in
the MFR_FAN_CONFIG command code. If the PWM duty
cycle has not reached the target value before the tem-
perature sample detects that a new PWM target value is
needed, the device stops moving toward the old target
and starts moving to the new target according to the
programmed ramp rate.
Table 7. Fan Control Operation Modes
Note: The RPM modes should only be used with fans that provide a tachometer output.
FAN CONTROL
MODE FAN OPERATIONAL DETAILS BIT 6 OF
FAN_CONFIG_1_2
VALUE IN
FAN_COMMAND_1
Manual PWM External host controls the fan speed by directly setting the fan
PWM duty-cycle values. 00000h to 7FFFh
Manual RPM
External host controls the fan speed by setting target fan speed
values. The device reads the actual fan speed and close loop
adjusts the output fan PWM to match the target fan speed.
10000h to 7FFFh
Automatic PWM
The device sets the output PWM based on the fan LUT that
maps the temperature sensor readings to the required fan PWM
duty-cycle values.
08000h to FFFFh
Automatic RPM
The device reads the actual fan speed and close loop adjusts
the output fan PWM to match the target fan speed based on
the fan LUT that maps the temperature sensor readings to the
required fan speed.
18000h to FFFFh
6-Channel Intelligent Fan Controller
MAX31785
23
Figure 1. Automatic Fan Control
Figure 2. Fan Speed Example
EACH FAN HAS A
UNIQUE 8-LEVEL LUT
HIGHEST TEMPERATURE
CONTROLS THE FAN
TEMP SENSOR TO
FAN MAPPING
OFFSET ADJUSTMENT
ALLOWS TEMPERATURE ZONE
NORMALIZATION
REMOTE DIODE
TEMP SENSOR 0 +15°C FAN 2
FAN 5
TEMP SENSOR DIODE 0
FAN 0 1 2 3 4 5
REMOTE DIODE
TEMP SENSOR 1 +10°C
TEMP SENSOR DIODE 1
FAN 0 1 2 3 4 5
REMOTE DIODE
TEMP SENSOR 2 0°C
TEMP SENSOR DIODE 2
FAN 0 1 2 3 4 5
I2C REMOTE
TEMP SENSOR 3 0°C
TEMP SENSOR I2C 3
FAN 0 1 2 3 4 5
INTERNAL
TEMP SENSOR +5°C
TEMP SENSOR INTERNAL
FAN 0 1 2 3 4 5
T1
T2
T3
T4
T5
T6
T7
SENSOR
TEMPERATURE
THERMAL
HYSTERESIS
T0
ELAPSED TIME
TEMPERATURE SAMPLE RATE
(ONCE PER SECOND)
S1
S2
S3
S4
S5
S6
S7
FAN SPEED
SAMPLE 1
SAMPLE 2 SAMPLE 3
SAMPLE 4
SAMPLED TEMPERATURES
S0
6-Channel Intelligent Fan Controller
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At temperature sample 2, the temperature has increased
to greater than temperature level 4 so again the PWM
duty cycle must be increased. At temperature sample
3, the temperature has dropped but not below the ther-
mal hysteresis level (which is set by the HYS bits in the
MFR_FAN_CONFIG command code), so the fan speed
remains at level 4. At temperature sample 4, the tem-
perature has dropped below the hysteresis point so the
PWM duty cycle is decreased.
Pulse Stretching
In some 3-wire fan applications, when the supply power
is interrupted to control fan speed, the tachometer sig-
nal is not available. Some fan controllers periodically
stretch the PWM signal to allow the tachometer to be
accurately detected. Pulse stretching can create audible
noise. This device does not implement pulse stretch-
ing. Hence, the RPM fan modes that require a reliable
tachometer signal to be available at all times should
not be used in applications that switch power to the fan
to control the speed of the fan. For example, low-side
switching of a 3-wire fan should not use either of the RPM
fan modes.
Fan Spin-Up
Figure 3 shows the fan spin-up process. When the fan is
spinning up, the number of revolutions is checked every
200ms for up to 2s. When the number of cumulated revo-
lutions is greater than or equal to the spin-up relaxation
criteria, the fan passes spin-up. If the fan has a locked
rotor output, fan spin-up passes when the locked rotor
signal is no longer asserted.
When spin-up passes, the device forces the fan PWM
with a 40% duty cycle. The 40% duty cycle is maintained
until the next temperature conversion is completed,
which occurs once a second. After the temperature con-
version, the device enters either manual mode operation
or automatic operation using MFR_FAN_LUT.
Figure 3. Fan Spin-Up
100% SPIN-UP
CRITERIA MET
AUTOMATIC
SPIN-UP
ENABLED
AUTOMATIC
SPIN-UP
DISABLED
ALWAYS RETURN TO 40% DUTY
CYCLE AFTER AUTOMATIC SPIN-UP
BEFORE BEGINNING PWM RAMP
(EVEN IF BEYOND 1 SECOND)
INITIAL TARGET PWM OR
RPM DETERMINED AFTER
TEMPERATURE CONVERSION
90%
80%
70%
60%
50%
40%
30%
20%
10%
0 0.2 0.4 0.6 0.8
TIME (SECONDS)
1.0 1.2 1.4
RAMP PWM TO TARGET PWM OR RPM
(CONSTRAINED BY THE RAMP BITS)
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Fan Power-On Sequencing
Multiple fans are not started at the same time. Fans are
started in increments of 200ms to relieve the strain on the
power supply. This sequencing occurs both at initial fan
power-up and when fans are turned off and on during
normal operation.
Fan Health-Meter Function
The device has a fan-health-diagnostic function to help
predict the remaining life of the fan. This function com-
pares the measured vs. expected fan speed for the
applied PWM duty cycle to determine if the fan is operat-
ing normally. This function is enabled with the HEALTH bit
(bit 4) in MFR_FAN_CONFIG. When the fan-health-meter
function is enabled, it runs once per second for each
enabled fan. If the fan’s PWM duty cycle has been stable
for 30s, the measured RPM is compared to the expect-
ed RPM and the correct fan-health-color bit (GREEN,
ORANGE, or RED) is set in STATUS_FAN_1_2. If the duty
cycle has been unstable for greater than 10 minutes, the
YELLOW bit is set in STATUS_FANS_1_2.
The expected fan-speed profile is entered with the
MFR_FAN_PWM2RPM command. With this command,
a table is filled with four preassigned PWM duty cycle
(40%, 60%, 80%, and 100%) vs. expected fan-speed
values, as shown in Figure 4. The comparison of the
measured RPM to expected RPM is performed when the
Figure 4. Fan PWM to RPM Example
EXPECTED FAN
SPEED IN RPM
EXPECTED FAN PWM
TO SPEED PROFILE
20 40 60 80
PWM DUTY CYCLE (%)
100
RPM@100% PWM
RPM@60% PWM
RPM@60% PWM
RPM@40% PWM
N
O
C
O
L
O
R
N
O
C
O
L
O
R
N
O
C
O
L
O
R
N
O
C
O
L
O
R
RED
RED
RED
ORANGE
ORANGE
GREEN
GREEN
RED
ORANGE
ORANGE
GREEN
GREEN
RED
RED
ORANGE
ORANGE
GREEN
GREEN
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Table 8. Fan Health Conditions
fan’s PWM duty cycle is between 40% and 80%. The
masured fan speed is also compared to the expected
at 100% duty cycle. In the 40% to 80% range, a fan’s
expected fan-speed profile is approximately linear. At
duty cycles outside this range (with the exception of
100%), the shape of the expected fan-speed profile
varies too much between fans, and it is not possible to
predict an expected speed.
A fan-health-color bit in STATUS_FANS_1_2 is set based
upon the difference between the measured and expect-
ed fan speed and the FAN_HEALTH_CRITERIA bits in
MFR_MODE, as shown in Table 8. If the fan PWM duty
cycle is less than 40% or between 80% and 100%, a
fan-health color cannot be assigned and all the color
bits are cleared. If the fan is unstable, the YELLOW color
bit is set.
LOWER NIBBLE OF
STATUS_FAN_1_2
FAN_HEALTH_CRITERIA BITS IN
MFR_MODE
MONITORED FAN SPEED VS.
EXPECTED TARGET
GREEN
00 Within 10%
01 Within 10%
10 Within 15%
11 Within 15%
YELLOW — Fan speed is not stable
ORANGE
00 Between 10% and 15%
01 Between 10% and 20%
10 Between 15% and 20%
11 Between 15% and 25%
RED
00 Over 15%
01 Over 20%
10 Over 20%
11 Over 25%
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PMBus Commands
A summary of the PMBus commands supported by the device are described in the following sections.
PAGE (00h)
The device can control up to six fans, up to 11 temperature sensors, and measure up to six remote voltages using one
PMBus (I2C) address. Send the PAGE command with data 0 to 22 to select which fan, temperature sensor, or remote
voltage fan is affected by all the PMBus commands shown in Table 1. Not all commands are supported within each
page. If an unsupported command is received, the CML status bit is set. Some commands are common, meaning that
any selected page has the same effect on and the same response from the device.
Set the PAGE to 255 when it is desired that the following PMBus commands should apply to all pages at the same time.
Table 9. Page Commands
PAGE (DEC) ASSOCIATED CONTROL
0Fan Connected to PWM 0
1Fan Connected to PWM 1
2Fan Connected to PWM 2
3Fan Connected to PWM 3
4Fan Connected to PWM 4
5Fan Connected to PWM 5
6Remote Thermal Diode Connected to ADC 0
7Remote Thermal Diode Connected to ADC 1
8Remote Thermal Diode Connected to ADC 2
9Remote Thermal Diode Connected to ADC 3
10 Remote Thermal Diode Connected to ADC 4
11 Remote Thermal Diode Connected to ADC 5
12 Internal Temperature Sensor
13 Remote I2C Temperature Sensor with Address 0
14 Remote I2C Temperature Sensor with Address 1
15 Remote I2C Temperature Sensor with Address 2
16 Remote I2C Temperature Sensor with Address 3
17 Remote Voltage Connected to ADC 0
18 Remote Voltage Connected to ADC 1
19 Remote Voltage Connected to ADC 2
20 Remote Voltage Connected to ADC 3
21 Remote Voltage Connected to ADC 4
22 Remote Voltage Connected to ADC 5
23 to 254 Reserved
255 Applies to All Pages
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CLEAR_FAULTS (03h)
The CLEAR_FAULTS command is used to clear any fault or warning bits in the status registers that have been set. This
command clears all bits simultaneously. If a fault is still present after the CLEAR_FAULTS command is executed, the
fault status bit is set again and the host is also notified by asserting ALERT (if enabled in MFR_MODE). This command
is write-only. There is no data byte for this command.
WRITE_PROTECT (10h)
The WRITE_PROTECT command is used to provide protection against accidental changes to the device operating
memory. All supported commands can have their parameters read, regardless of the WRITE_PROTECT settings. The
WRITE_PROTECT message content is described in Table 10.
Table 10. WRITE_PROTECT Command Byte
Note: No fault or error is generated if the host attempts to write to a protected area.
STORE_DEFAULT_ALL (11h)
The STORE_DEFAULT_ALL command instructs the device to transfer the device configuration information to the
internal flash memory array. Not all information is stored. Only configuration data is stored, not any status or opera-
tional data. If an error occurs during the transfer, ALERT asserts if enabled and the CML bit in STATUS_BYTE and
STATUS_WORD is set to 1. No bits are set in STATUS_CML. It is NOT recommended to use the STORE_DEFAULT_ALL
command while the device is operating fans. The device is unresponsive to PMBus commands and does not monitor
fans while transferring the configuration. After this command is sent, another command should not be sent for at least
250ms. This command is write-only. There is no data byte for this command.
USER NOTE: VDD must be above 2.9V for the device to perform the STORE_DEFAULT_ALL command.
RESTORE_DEFAULT_ALL (12h)
The RESTORE_DEFAULT_ALL command transfers the default configuration information from the internal flash memory
array to the user memory registers in the device. The RESTORE_DEFAULT_ALL command should only be executed
when the device is not operating the fans. Upon a device reset, this command is automatically executed by the device
without PMBus action required. After this command is sent, another command should not be sent for at least 250ms.
This command is write-only. There is no data byte for this command.
CAPABILITY (19h)
The CAPABILITY command is used to determine some key capabilities of the device. The CAPABILITY command is
read-only. The message content is described in Table 11.
Table 11. CAPABILITY Command Byte
COMMAND BYTE MEANING
80h Disable all writes except the WRITE_PROTECT command.
40h Disable all writes except the WRITE_PROTECT and PAGE commands.
00h Enable writes for all commands (default).
BIT DESCRIPTION MEANING
7Packet-Error Checking 0 = PEC not supported.
6:5 PMBus Speed 00 = Maximum supported bus speed is 100kHz.
4 ALERT 1 = Device supports an ALERT output (if ALERT is enabled in MFR_MODE).
0 = Device does not support ALERT output (ALERT is disabled in MFR_MODE).
3:0 Reserved Always returns 0000.
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VOUT_MODE (20h)
The VOUT_MODE command is used to report the data format of the device. The device uses the DIRECT format for all
the voltage-related commands. The value returned is 40h, indicating DIRECT data format. This command is read-only.
If a host attempts to write this command, the CML status bit is asserted. See Table 3 for the m, b, and R values for the
various commands.
VOUT_SCALE_MONITOR (2Ah)
VOUT_SCALE_MONITOR is used in applications where the measured remote voltage is not equal to the voltage at the
ADC input. For example, if the ADC input expects a 1.0V input for a 12V output, VOUT_SCALE_MONITOR = 1.0V/12V
= 0.0833. In applications where the remote voltage is greater than the device input range, the voltage of the remote
supply is sensed through a resistive voltage-divider. The resistive voltage-divider reduces or scales the remote voltage.
The PMBus commands specify the actual remote voltages and not the input voltage to the ADC. To allow the device to
map between the remote voltage (such as 12V) and the voltage at the ADC input, the VOUT_SCALE_MONITOR com-
mand is used. The 2 data bytes are in DIRECT format. This value is dimensionless. For example, if the required scaling
factor is 0.0833, then VOUT_SCALE_MONITOR should be set to 0AABh (2731/32,767 = 0.0833).
Table 12. VOUT_SCALE_MONITOR
USER NOTE: On the device, the full-scale ADC voltage is 1.225V. The scaling factor where a 1.0V ADC input
represents a nominal 100% voltage level is recommended.
FAN_CONFIG_1_2 (3Ah)
The FAN_CONFIG_1_2 command is used in conjunction with MFR_FAN_CONFIG to configure the fan. See the
MFR_FAN_CONFIG (F1h) section for more details on this command. The FAN_CONFIG_1_2 command is described
in Table 13.
Table 13. FAN_CONFIG_1_2 Command Byte
NOMINAL VOLTAGE LEVEL
MONITORED (V)
NOMINAL ADC INPUT VOLTAGE
LEVEL (V) (SEE NOTE)
RESISTIVE VOLTAGE-
DIVIDER RATIO
VOUT_SCALE_MONITOR
VALUE (HEX)
1.2 1.0 0.833 6AAAh
1.5 1.0 0.667 5555h
1.8 1.0 0.555 470Ah
2.5 1.0 0.4 3333h
3.3 1.0 0.303 26C8h
5 1.0 0.2 1999h
12 1.0 0.0833 0AABh
BIT NAME MEANING
7FAN ENABLE 0 = Fan disabled (PWM forced low).
1 = Fan enabled.
6 RPM/PWM 0 = PWM duty cycle is the fan-controlling parameter.
1 = RPM is the fan-controlling parameter.
5:4 PULSE
00 = 1 Tach pulse per fan revolution.
01 = 2 Tach pulses per fan revolution.
10 = 3 Tach pulses per fan revolution.
11 = 4 Tach pulses per fan revolution.
3:0 0 These bits always return a 0.
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FAN_COMMAND_1 (3Bh)
The FAN_COMMAND_1 command is used to override the device’s automatic fan-control function and force the fan to
either a fixed PWM duty-cycle value or a target fan speed (in RPM). The units of FAN_COMMAND_1 are either percent
duty cycle (if bit 6 of FAN_CONFIG_1_2 is zero) or RPM (if bit 6 of FAN_CONFIG_1_2 is one). Any value less than 0%
duty cycle or 0 RPM causes the device to ignore this command and use the automatic fan-control function. Any value
greater than or equal to 0% duty cycle or 0 RPM causes the device to ignore the automatic fan-control function and
force the fan to the PWM value or RPM value provided by the FAN_COMMAND_1 command. The 2 data bytes are in
DIRECT format.
Table 14. PWM Fan Mode (FAN_CONFIG_1_2 Bit 6 = 0)
Table 15. RPM Fan Mode (FAN_CONFIG_1_2 Bit 6 = 1)
VOUT_OV_FAULT_LIMIT (40h)
The VOUT_OV_FAULT_LIMIT command sets the value of the output voltage that causes an output overvoltage fault.
The monitored voltage must drop by at least 2% below the limit before the fault is allowed to clear. The 2 data bytes
are in DIRECT format. In response to the VOUT_OV_FAULT_LIMIT being exceeded, the device does the following:
1) Sets the VOUT_OV bit in STATUS_BYTE.
2) Sets the VOUT_OV and VOUT bits in STATUS_WORD.
3) Sets the VOUT_OV_FAULT bit in STATUS_VOUT.
4) Responds as specified in the MFR_FAULT_RESPONSE.
5) Notifies the host through ALERT assertion (if enabled in MFR_MODE).
VOUT_OV_WARN_LIMIT (42h)
The VOUT_OV_WARN_LIMIT command sets the value of the output voltage that causes an output-voltage high warn-
ing. This value is typically less than the output overvoltage threshold in VOUT_OV_FAULT_LIMIT. The monitored volt-
age must drop by at least 2% below the limit before the warning is allowed to clear. The 2 data bytes are in DIRECT
format. In response to the VOUT_OV_WARN_LIMIT being exceeded, the device does the following:
1) Sets the NONE OF THE ABOVE bit in STATUS_BYTE.
2) Sets the NONE OF THE ABOVE and VOUT bits in STATUS_WORD.
3) Sets the VOUT_OV_WARN bit in STATUS_VOUT.
4) Notifies the host using ALERT assertion (if enabled in MFR_MODE).
FAN_COMMAND_1 VALUE DEVICE RESPONSE
8000h to FFFFh Ignore FAN_COMMAND_1 and use automatic fan-control function
0000h to 2710h 0 to 100% fan PWM duty cycle
2711h to 7FFFh 100% fan PWM duty cycle
FAN_COMMAND_1 VALUE DEVICE RESPONSE
8000h to FFFFh Ignore FAN_COMMAND_1 and use automatic fan-control function
0000h to 7FFFh 0 to 32,767 RPM
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VOUT_UV_WARN_LIMIT (43h)
The VOUT_UV_WARN_LIMIT command sets the value of the output voltage that causes an output-voltage low warning.
This value is typically greater than the output undervoltage fault threshold in VOUT_UV_FAULT_LIMIT. The monitored
voltage must increase by at least 2% above the limit before the warning is allowed to clear. The 2 data bytes are in
DIRECT format. In response to violation of the VOUT_UV_WARN_LIMIT, the device does the following:
1) Sets the NONE OF THE ABOVE bit in STATUS_BYTE.
2) Sets the NONE OF THE ABOVE and VOUT bits in STATUS_WORD.
3) Sets the VOUT_UV_WARN bit in STATUS_VOUT.
4) Notifies the host using ALERT assertion (if enabled in MFR_MODE).
VOUT_UV_FAULT_LIMIT (44h)
The VOUT_UV_FAULT_LIMIT command sets the value of the output voltage that causes an output undervoltage fault.
The monitored voltage must increase by at least 2% above the limit before the fault is allowed to clear. The 2 data bytes
are in DIRECT format. In response to violation of the VOUT_UV_FAULT_LIMIT, the device does the following:
1) Sets the NONE OF THE ABOVE bit in STATUS_BYTE.
2) Sets the NONE OF THE ABOVE and VOUT bits in STATUS_WORD.
3) Sets the VOUT_UV_FAULT bit in STATUS_VOUT.
4) Responds as specified in MFR_FAULT_RESPONSE.
5) Notifies the host using ALERT assertion (if enabled in MFR_MODE).
OT_FAULT_LIMIT (4Fh)
The OT_FAULT_LIMIT command sets the temperature, in degrees Celsius, of the selected temperature sensor at which an
overtemperature fault is detected. The monitored temperature must drop by at least 4°C below the limit before the fault is
allowed to clear. The 2 data bytes are in DIRECT format. In response to the OT_FAULT_LIMIT being exceeded, the device
does the following:
1) Sets the TEMPERATURE bit in STATUS_BYTE.
2) Sets the TEMPERATURE and MFR bits in STATUS_WORD.
3) Sets the OT_FAULT bit in STATUS_MFR_SPECIFIC.
4) Responds as specified in MFR_FAULT_RESPONSE.
5) Notifies the host using ALERT assertion (if enabled in MFR_MODE).
OT_WARN_LIMIT (51h)
The OT_WARN_LIMIT command sets the temperature, in degrees Celsius, of the selected temperature sensor at which
an overtemperature warning is detected. The monitored temperature must drop by at least 4°C below the limit before
the warning is allowed to clear. The 2 data bytes are in DIRECT format. In response to the OT_WARN_LIMIT being
exceeded, the device does the following:
1) Sets the TEMPERATURE bit in STATUS_BYTE.
2) Sets the TEMPERATURE and MFR bits in STATUS_WORD.
3) Sets the OT_WARN bit in STATUS_MFR_SPECIFIC.
4) Notifies the host through ALERT assertion (if enabled in MFR_MODE).
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STATUS_BYTE (78h)
The STATUS_BYTE command returns 1 byte of information with a summary of the most critical faults. A value of 1 indi-
cates that a fault or warning event has occurred and a 0 indicates otherwise. Bits for unsupported features are reported
as 0. The STATUS_BYTE cannot be restored by the RESTORE_DEFAULT_ALL command. The STATUS_BYTE message
content is described in Table 16. This command is read-only.
STATUS_WORD (79h)
The STATUS_WORD command returns 2 bytes of information with a summary of the reason for a fault. The low byte of
the STATUS_WORD is the same data as the STATUS_BYTE. Table 17 describes the STATUS_WORD message content.
STATUS_VOUT (7Ah)
The STATUS_VOUT command returns 1 byte of information with contents as described in Table 18.
Table 16. STATUS_BYTE
Table 17. STATUS_WORD
Table 18. STATUS_VOUT
BIT BIT NAME MEANING
7:6 0 These bits always return a 0.
5 VOUT_OV An overvoltage fault has occurred.
4:3 0 These bits always return a 0.
2 TEMPERATURE A temperature fault or warning has occurred.
1 CML A communication, memory, or logic fault has occurred.
0NONE OF THE ABOVE A fault or warning not listed in bits [7:1] has occurred.
BIT BIT NAME MEANING
15 VOUT An output voltage fault or warning has occurred.
14:13 0 These bits always return a 0.
12 MFR A bit in STATUS_MFR_SPECIFIC has been set.
11 0 This bit always returns a 0.
10 FANS A fan fault or warning has occurred.
9:6 0 These bits always return a 0.
5 VOUT_OV An overvoltage fault has occurred.
4:3 0 These bits always return a 0.
2 TEMPERATURE A temperature fault or warning has occurred.
1 CML A communication, memory, or logic fault has occurred.
0NONE OF THE ABOVE A fault or warning not listed in bits [7:1] has occurred.
BIT BIT NAME MEANING
7 VOUT_OV_FAULT VOUT overvoltage fault.
6 VOUT_OV_WARN VOUT overvoltage warning.
5 VOUT_UV_WARN VOUT undervoltage warning.
4 VOUT_UV_FAULT VOUT undervoltage fault.
3:0 0 These bits always return a 0.
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STATUS_CML (7Eh)
The STATUS_CML command returns 1 byte of information with contents as described in Table 19.
STATUS_MFR_SPECIFIC (80h)
The STATUS_MFR_SPECIFIC command returns 1 byte of information with a summary of the reason for a fault. The
STATUS_MFR_SPECIFIC message content is described in Table 20.
STATUS_FANS_1_2 (81h)
The STATUS_FANS_1_2 command returns 1 byte of information with the status of the fan. The STATUS_FANS_1_2
command is described in Table 21.
Table 19. STATUS_CML
Table 20. STATUS_MFR_SPECIFIC
Note: The settings of the RED, ORANGE, YELLOW, and GREEN bits does not assert the ALERT signal.
Table 21. STATUS_FANS_1_2
BIT BIT NAME MEANING
7 COMM_FAULT An invalid or unsupported command has been received.
6 DATA_FAULT An invalid or unsupported data has been received.
5:1 0 These bits always return a 0.
0 FAULT_LOG_FULL MFR_NV_FAULT_LOG is full and needs to be cleared.
BIT BIT NAME MEANING
7 0 This bit always returns a 0.
6 OT_WARN Overtemperature warning.
5 OT_FAULT Overtemperature fault.
4 WATCHDOG A watchdog reset has occurred.
3:0 0 These bits always return a 0.
BIT BIT NAME MEANING
7 FAN_1_FAULT Fan 1 fault.
6 0 This bit always returns a 0.
5 FAN_1_WARN Fan 1 warning.
4 0 This bit always returns a 0.
3 RED The lower nibble reports the estimated health of the fan. Only one of the four bits is set at any
one time. If no bits are set, the fan health cannot be estimated. RED is the worst health state
and GREEN is the best health state. The CLEAR_FAULTS command does not affect these
bits.
2 ORANGE
1 YELLOW
0 GREEN
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READ_VOUT (8Bh)
The READ_VOUT command returns the actual measured output voltage. READ_VOUT is measured and updated every
10ms. The 2 data bytes are in DIRECT format.
READ_TEMPERATURE_1 (8Dh)
The READ_TEMPERATURE_1 command returns the temperature returned from the temperature sensor. The value of
READ_TEMPERATURE_1 does not have offset from MFR_TEMP_SENSOR_CONFIG added. READ_TEMPERATURE_1
returns 7FFFh if the sensor is faulty and 0000h if the sensor is disabled. READ_TEMPERATURE_1 is measured and
updated once a second. The 2 data bytes are in DIRECT format.
READ_FAN_SPEED_1 (90h)
The READ_FAN_SPEED_1 command returns the fan speed in RPM. READ_FAN_SPEED_1 is updated once a second,
even if the fan is disabled. The PULSE bits in FAN_CONFIG_1_2 must be properly configured to receive the correct
fan speed. Fan speeds below 60 RPM (360 RPM for dual mode fans) are reported as 0 RPM. The 2 data bytes are in
DIRECT format.
PMBUS_REVISION (98h)
The PMBUS_REVISION command returns the revision of the PMBus specification to which the device is compliant. The
command has 1 data byte. Bits [7:4] indicate the revision of PMBus specification Part I to which the device is compli-
ant. Bits [3:0] indicate the revision of PMBus specification Part II to which the device is compliant. This command is
read-only. The PMBUS_REVISION value returned is always 11h, which indicates that it is compliant with Part I Rev 1.1
and Part II Rev 1.1.
MFR_ID (99h)
The MFR_ID command returns the text (ISO/IEC 8859-1) character of the manufacturer’s (Maxim) identification. The
default MFR_ID value is 4Dh (M). This command is read-only.
MFR_MODEL (9Ah)
The MFR_MODEL command returns the text (ISO/IEC 8859-1) character of the device model number. The default
MFR_MODEL value is 53h (S). This command is read-only.
MFR_REVISION (9Bh)
The MFR_REVISION command returns two text (ISO/IEC 8859-1) characters that contain the device revision numbers
for hardware (upper byte) and firmware (lower byte). The default MFR_REVISION value is 3030h (00). This command
is read-only.
MFR_LOCATION (9Ch)
The MFR_LOCATION command loads the device with text (ISO/IEC 8859-1) characters that identify the facility that
manufactures the equipment. The maximum number of characters is 8. This data is written to internal flash using the
STORE_DEFAULT_ALL command. The factory default text string value is 10101010.
MFR_DATE (9Dh)
The MFR_DATE command loads the device with text (ISO/IEC 8859-1) characters that identify the date of manu-
facture of the equipment. The maximum number of characters is 8. This data is written to internal flash using the
STORE_DEFAULT_ALL command. The factory default text string value is 10101010.
MFR_SERIAL (9Eh)
The MFR_SERIAL command loads the device with text (ISO/IEC 8859-1) characters that uniquely identify the equipment.
The maximum number of characters is 8. This data is written to internal flash using the STORE_DEFAULT_ALL com-
mand. The factory default text string value is 10101010.
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MFR_MODE (D1h)
The MFR_MODE command is used to configure the device to support manufacturer specific commands. The MFR_
MODE command is described in Table 22. After this command is sent, another command should not be sent for at
least 250ms.
Table 22. MFR_MODE
BIT BIT NAME MEANING
15 FORCE_NV_FAULT_LOG
Setting this bit to 1 forces the device to log data into the nonvolatile fault log. Once set, the
device clears this bit when the action is completed. The host must set again for subsequent
action. If an error occurs during this action, the device sets the CML bit in STATUS_BYTE
and STATUS_WORD; no bits are set in STATUS_CML.
14 CLEAR_NV_FAULT_LOG
Setting this bit to 1 forces the device to clear the nonvolatile fault log by writing FFh to all
byte locations. Once set, the device clears this bit when the action is completed. The host
must set again for subsequent action. If an error occurs during this action, the device sets
the CML bit in STATUS_BYTE and STATUS_WORD; no bits are set in STATUS_CML.
13 ALERT 0 = ALERT disabled (device does not respond to ARA).
1 = ALERT enabled (device responds to ARA and ARA must be used).
12 0 This bit always returns a 0.
11 SOFT_RESET This bit must be set, then cleared and set again within 8ms for a soft reset to occur.
10:8 0 These bits always return a 0.
7:6 FAN_HEALTH_CRITERIA
These bits select the threshold for the expected RPM in the fan health monitor.
BIT GREEN ORANGE RED
0 0 < 10% < 15% > 15%
0 1 < 10% < 20% > 20%
1 0 < 15% < 20% > 20%
1 1 < 15% < 25% > 25%
5 ADC5_ENABLE 0 = ADC5 voltage sense disabled.
1 = ADC5 voltage sense enabled (overridden if temp sense enabled)
4 ADC4_ENABLE 0 = ADC4 voltage sense disabled.
1 = ADC4 voltage sense enabled (overridden if temp sense enabled)
3 ADC3_ENABLE 0 = ADC3 voltage sense disabled.
1 = ADC3 voltage sense enabled (overridden if temp sense enabled)
2 ADC2_ENABLE 0 = ADC2 voltage sense disabled.
1 = ADC2 voltage sense enabled (overridden if temp sense enabled)
1 ADC1_ENABLE 0 = ADC1 voltage sense disabled.
1 = ADC1 voltage sense enabled (overridden if temp sense enabled)
0 ADC0_ENABLE 0 = ADC0 voltage sense disabled.
1 = ADC0 voltage sense enabled (overridden if temp sense enabled)
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MFR_VOUT_PEAK (D4h)
The MFR_VOUT_PEAK command returns the maximum actual measured output voltage. To reset this value to 0, write to this
command with a data value of 0. Any values written to this command are used as a comparison for future peak updates. The
2 data bytes are in DIRECT format.
MFR_TEMPERATURE_PEAK (D6h)
The MFR_TEMPERATURE_PEAK command returns the maximum measured temperature. To reset this value to its low-
est value, write to this command with a data value of 8000h. Any other values written by this command are used as a
comparison for future peak updates. The 2 data bytes are in DIRECT format.
MFR_VOUT_MIN (D7h)
The MFR_VOUT_MIN command returns the minimum actual measured output voltage. To reset this value, write to this com-
mand with a data value of 7FFFh. Any values written to this command are used as a comparison for future minimum updates.
The 2 data bytes are in DIRECT format.
MFR_FAULT_RESPONSE (D9h)
The MFR_FAULT_RESPONSE command specifies the response to each fault condition supported by the device. In
response to a fault, the device always report the fault in the appropriate status register and asserts the ALERT output
(if enabled in MFR_MODE). A CML fault cannot cause any device action other than setting the status bit and asserting
the ALERT output. The MFR_FAULT_RESPONSE command is described in Table 23.
Table 23. MFR_FAULT_RESPONSE
Note 1: For fault responses, a fault is defined as either a fan fault, an overtemperature fault, or an undervoltage fault. Bits 2 and 6
allow the addition of an overvoltage fault to the fault definition.
Note 2: If FAULT_PIN_MONITOR = 1, the device reacts to both internal and external assertions of the FAULT pin.
BIT BIT NAME MEANING
7 NV_LOG 0 = Do not log the fault into MFR_NV_FAULT_LOG.
1 = Log the fault into MFR_NV_FAULT_LOG.
6 NV_LOG_OV
This bit is only valid for pages 17 to 22. Other pages always return a 0.
0 = Bit 7 is ignored for overvoltage faults.
1 = Bit 7 also applies to overvoltage faults.
5 UV_OV_FILTER
This bit is only valid for pages 17 to 22. Other pages always return a 0.
0 = Fault or warning on first voltage sample excursion occurrence.
1 = Requires two consecutive voltage sample excursions before a fault or warning
is declared and action taken.
4:3 0 These bits always return a 0.
2 FAULT_PIN_ENABLE_OV
This bit is only valid for pages 17 to 22. Other pages always return a 0.
0 = Bit 1 is ignored for overvoltage faults.
1 = Bit 1 also applies to overvoltage faults.
1 FAULT_PIN_ENABLE 0 = Never assert the FAULT pin.
1 = Assert the FAULT pin during an active fault.
0 FAULT_PIN_MONITOR
This bit is only valid for pages 0 to 5. Other pages always return a 0.
0 = Ignore the FAULT pin.
1 = Force fan to 100% PWM duty cycle when the FAULT pin is asserted.
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MFR_NV_FAULT_LOG (DCh)
Each time the MFR_NV_FAULT_LOG command is executed, the device returns a block of 255 bytes containing one
of the 15 nonvolatile fault logs. The MFR_NV_FAULT_LOG command must be executed 15 times to dump the com-
plete nonvolatile fault log. If the returned fault log is all FFs, this indicates that this fault log has not been written by the
device. As the device is operating, it is reading the latest operating conditions for fan speed, voltage, and temperature,
and it is updating the status registers. All this information is stored in on-board RAM. When a fault is detected (if so
enabled in MFR_FAULT_RESPONSE), the device automatically logs this information to one of the 15 nonvolatile fault
logs. After 15 faults have been written, bit 0 of STATUS_CML is set and the host must clear the fault log by setting the
CLEAR_NV_FAULT_LOG bit in MFR_MODE before any additional faults are logged. All the latest status information is
logged as well as eight readings of voltage from the last 800ms in 100ms increments. If a fan is not enabled or if volt-
age or a temperature sensor is disabled, the associated fault log position returns 0000h.
There is a FAULT_LOG_COUNT (16-bit counter) at the beginning of each fault log that indicates which fault log is
the latest. This counter rolls over should more than 65,535 faults be logged. This counter is not cleared when the
CLEAR_NV_FAULT_LOG bit in MFR_MODE is toggled. The 255 bytes returned by the MFR_NV_FAULT_LOG com-
mand are described in Table 24.
If an error occurs while the device is attempting to write or clear the NV_FAULT_LOG, the device sets the CML bit in
STATUS_BYTE and STATUS_WORD; no bits are set in STATUS_CML. ALERT is asserted (if enabled in MFR_MODE).
See Figure 5.
USER NOTE: VDD must be above 2.9V for the device to clear or log data into MFR_NV_FAULT_LOG.
Figure 5. MFR_NV_FAULT_LOG
FAULT LOG INDEX 0
(255 BYTES)
FAULT LOG INDEX 1
(255 BYTES)
FAULT LOG INDEX 2
(255 BYTES)
STATUS
VOLTAGE
TEMPERATURE
FAN SPEED
RAM
FLASHEACH FAULT IS WRITTEN INTO
THE NEXT FAULT LOG
EACH COMMAND READ
ACCESSES THE NEXT FAULT LOG
FAULT OCCURENCE
FAULT LOG INDEX 14
(255 BYTES)
MFR_NV_FAULT_LOG
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Table 24. MFR_NV_FAULT_LOG
BYTE PARAMETER BYTE PARAMETER
0 00h/FAULT_LOG_INDEX 128 READ_VOUT Index = 3, Page 19
2 FAULT_LOG_COUNT 130 READ_VOUT Index = 3, Page 20
4MFR_TIME_COUNT (LSW) 132 READ_VOUT Index = 3, Page 21
6MFR_TIME_COUNT (MSW) 134 READ_VOUT Index = 3, Page 22
8 STATUS_BYTE/STATUS_CML 136 READ_VOUT Index = 4, Page 17
10 STATUS_WORD 138 READ_VOUT Index = 4, Page 18
12 STATUS_VOUT Pages 17/18 140 READ_VOUT Index = 4, Page 19
14 STATUS_VOUT Pages 19/20 142 READ_VOUT Index = 4, Page 20
16 STATUS_VOUT Pages 21/22 144 READ_VOUT Index = 4, Page 21
18 STATUS_MFR_SPECIFIC Pages 6/7 146 READ_VOUT Index = 4, Page 22
20 STATUS_MFR_SPECIFIC Pages 8/9 148 READ_VOUT Index = 5, Page 17
22 STATUS_MFR_SPECIFIC Pages 10/11 150 READ_VOUT Index = 5, Page 18
24 STATUS_MFR_SPECIFIC Pages 12/13 152 READ_VOUT Index = 5, Page 19
26 STATUS_MFR_SPECIFIC Pages 14/15 154 READ_VOUT Index = 5, Page 20
28 STATUS_MFR_SPECIFIC Pages 16/00h 156 READ_VOUT Index = 5, Page 21
30 STATUS_FANS_1_2 Pages 0/1 158 READ_VOUT Index = 5, Page 22
32 STATUS_FANS_1_2 Pages 2/3 160 READ_VOUT Index = 6, Page 17
34 STATUS_FANS_1_2 Pages 4/5 162 READ_VOUT Index = 6, Page 18
36 MFR_VOUT_PEAK Page 17 164 READ_VOUT Index = 6, Page 19
38 MFR_VOUT_PEAK Page 18 166 READ_VOUT Index = 6, Page 20
40 MFR_VOUT_PEAK Page 19 168 READ_VOUT Index = 6, Page 21
42 MFR_VOUT_PEAK Page 20 170 READ_VOUT Index = 6, Page 22
44 MFR_VOUT_PEAK Page 21 172 READ_VOUT Index = 7, Page 17
46 MFR_VOUT_PEAK Page 22 174 READ_VOUT Index = 7, Page 18
48 MFR_TEMPERATURE_PEAK Page 6 176 READ_VOUT Index = 7, Page 19
50 MFR_TEMPERATURE_PEAK Page 7 178 READ_VOUT Index = 7, Page 20
52 MFR_TEMPERATURE_PEAK Page 8 180 READ_VOUT Index = 7, Page 21
54 MFR_TEMPERATURE_PEAK Page 9 182 READ_VOUT Index = 7, Page 22
56 MFR_TEMPERATURE_PEAK Page 10 184 READ_FAN_SPEED_1 Page 0
58 MFR_TEMPERATURE_PEAK Page 11 186 READ_FAN_SPEED_1 Page 1
60 MFR_TEMPERATURE_PEAK Page 12 188 READ_FAN_SPEED_1 Page 2
62 MFR_TEMPERATURE_PEAK Page 13 190 READ_FAN_SPEED_1 Page 3
64 MFR_TEMPERATURE_PEAK Page 14 192 READ_FAN_SPEED_1 Page 4
66 MFR_TEMPERATURE_PEAK Page 15 194 READ_FAN_SPEED_1 Page 5
68 MFR_TEMPERATURE_PEAK Page 16 196 MFR_READ_FAN_PWM Page 0
70 MFR_VOUT_MIN Page 17 198 MFR_READ_FAN_PWM Page 1
72 MFR_VOUT_MIN Page 18 200 MFR_READ_FAN_PWM Page 2
74 MFR_VOUT_MIN Page 19 202 MFR_READ_FAN_PWM Page 3
76 MFR_VOUT_MIN Page 20 204 MFR_READ_FAN_PWM Page 4
78 MFR_VOUT_MIN Page 21 206 MFR_READ_FAN_PWM Page 5
80 MFR_VOUT_MIN Page 22 208 MFR_FAN_RUN_TIME Page 0
82 RESERVED (0000h) 210 MFR_FAN_RUN_TIME Page 1
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Table 24. MFR_NV_FAULT_LOG (continued)
Note: LOG_VALID is set to DDh if the fault log contains valid data.
BYTE PARAMETER BYTE PARAMETER
84 RESERVED (0000h) 212 MFR_FAN_RUN_TIME Page 2
86 VOLTAGE_INDEX/00h 214 MFR_FAN_RUN_TIME Page 3
88 READ_VOUT Index = 0, Page 17 216 MFR_FAN_RUN_TIME Page 4
90 READ_VOUT Index = 0, Page 18 218 MFR_FAN_RUN_TIME Page 5
92 READ_VOUT Index = 0, Page 19 220 MFR_FAN_PWM_AVG Page 0
94 READ_VOUT Index = 0, Page 20 222 MFR_FAN_PWM_AVG Page 1
96 READ_VOUT Index = 0, Page 21 224 MFR_FAN_PWM_AVG Page 2
98 READ_VOUT Index = 0, Page 22 226 MFR_FAN_PWM_AVG Page 3
100 READ_VOUT Index = 1, Page 17 228 MFR_FAN_PWM_AVG Page 4
102 READ_VOUT Index = 1, Page 18 230 MFR_FAN_PWM_AVG Page 5
104 READ_VOUT Index = 1, Page 19 232 READ_TEMPERATURE_1 Page 6
106 READ_VOUT Index = 1, Page 20 234 READ_TEMPERATURE_1 Page 7
108 READ_VOUT Index = 1, Page 21 236 READ_TEMPERATURE_1 Page 8
110 READ_VOUT Index = 1, Page 22 238 READ_TEMPERATURE_1 Page 9
112 READ_VOUT Index = 2, Page 17 240 READ_TEMPERATURE_1 Page 10
114 READ_VOUT Index = 2, Page 18 242 READ_TEMPERATURE_1 Page 11
116 READ_VOUT Index = 2, Page 19 244 READ_TEMPERATURE_1 Page 12
118 READ_VOUT Index = 2, Page 20 246 READ_TEMPERATURE_1 Page 13
120 READ_VOUT Index = 2, Page 21 248 READ_TEMPERATURE_1 Page 14
122 READ_VOUT Index = 2, Page 22 250 READ_TEMPERATURE_1 Page 15
124 READ_VOUT Index = 3, Page 17 252 READ_TEMPERATURE_1 Page 16
126 READ_VOUT Index = 3, Page 18 254 LOG_VALID (see note)
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MFR_TIME_COUNT (DDh)
The MFR_TIME_COUNT command returns the number of seconds of device lifetime operation. Once every hour, the
device automatically stores this counter in flash memory. The counter is a 32-bit value that rolls over. The latest stored
value is automatically recalled from flash memory upon device power cycle, RST action, or a soft reset. This count
can be reset to zero by writing a sequence of all zeros (00000000h), followed by all ones (FFFFFFFFh), followed by all
zeros (00000000h) within 8ms.
MFR_TEMP_SENSOR_CONFIG (F0h)
The MFR_TEMP_SENSOR_CONFIG command is used to configure the temperature sensors. Table 25 describes the
MFR_TEMP_SENSOR_CONFIG command.
Table 25. MFR_TEMP_SENSOR_CONFIG
BIT BIT NAME MEANING
15 ENABLE 0 = Temperature sensor disabled.
1 = Temperature sensor enabled.
14:10 OFFSET
The OFFSET setting is used to allow the temperature reading to be normalized among multiple
temperature sensors. Values from 00h to 1Eh select the offset value. The valid range is 0NC to
+30NC in 1NC steps. If OFFSET is 1Fh, the device automatically uses the value written to the
OT_WARN_LIMIT command code for the LUT instead of the digitized measured temperature.
OFFSET VALUE CONFIGURATION
00h Offset = 0NC
01h Offset = +1NC
02h Offset = +2NC
1Dh Offset = +29NC
1Eh Offset = +30NC
1Fh Test Mode
9:6 0 These bits always return a 0.
5 FAN5 0 = Temperature sensor is not used to control fan 5 speed.
1 = Temperature sensor is used to control fan 5 speed.
4 FAN4 0 = Temperature sensor is not used to control fan 4 speed.
1 = Temperature sensor is used to control fan 4 speed.
3 FAN3 0 = Temperature sensor is not used to control fan 3 speed.
1 = Temperature sensor is used to control fan 3 speed.
2 FAN2 0 = Temperature sensor is not used to control fan 2 speed.
1 = Temperature sensor is used to control fan 2 speed.
1 FAN1 0 = Temperature sensor is not used to control fan 1 speed.
1 = Temperature sensor is used to control fan 1 speed.
0 FAN0 0 = Temperature sensor is not used to control fan 0 speed.
1 = Temperature sensor is used to control fan 0 speed.
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MFR_FAN_CONFIG (F1h)
The MFR_FAN_CONFIG command is used with FAN_CONFIG_1_2 to configure the fan. See the FAN_CONFIG_1_2
description for more details on this command. Table 26 describes the MFR_FAN_CONFIG command.
Table 26. MFR_FAN_CONFIG
BIT BIT NAME MEANING
15:13 FREQ[2:0]
The FREQ bits set the PWM frequency. Note: The device does not support pulse stretching.
FREQ2 FREQ1 FREQ0 PWM FREQUENCY
0 0 0 30Hz
0 0 1 50Hz
0 1 0 100Hz
0 1 1 150Hz
1 0 0 Reserved
1 0 1 Reserved
1 1 0 Reserved
1 1 1 25kHz
12 DUAL_TACH
0 = Dual tach functionality is disabled.
1 = Dual tach functionality is enabled.
Note: In dual tachometer applications, it is recommended that the slower tachometer signal be
presented to the TACH pin when TACHSEL = 0.
11:10 HYS[1:0]
The HYS bits determine the amount of hysteresis the device uses to determine how far the tem-
perature must fall below the temperature level threshold programmed in the LUT before switch-
ing to the lower PWM/RPM value. The hysteresis should be set lower than the minimum differ-
ence between two adjacent temperature steps. These bits are ignored if automatic fan control is
disabled.
HSY1 HSY0 THERMAL HYSTERESIS (NC)
0 0 2
0 1 4
1 0 6
1 1 8
9 TSFO
0 = Ramp to 100% PWM duty cycle if temp sensor faults (automatic fan mode) or if no
FAN_COMMAND_1 update occurs (manual fan mode) in any 10s period.
1 = Temp sensor fault or update rate to FAN_COMMAND_1 is ignored. Operate at the last
updated PWM/RPM value.
Note 1: A temp sensor fault is a faulty temperature sensor reading, not an overtemperature fault.
Note 2: In automatic fan mode, if the TSFO bit is set to 1, the device ignores a sensor fault and
uses the remaining assigned temperature sensors (if any) to control the fan PWM duty cycle; or,
if the fan has no available temperature sensors to use, it maintains the last updated PWM/RPM
fan value before the fault occurred.
8 TACHO
0 = Ramp fan to 100% PWM duty cycle if fan fault is detected.
1 = Do not ramp fan to 100% PWM duty cycle if fan fault is detected.
Note: If the fan fault is removed after ramping the PWM to 100% duty cycle, normal fan opera-
tion is resumed.
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Table 26. MFR_FAN_CONFIG (continued)
Note: It is recommended that the fan be disabled prior to changing MFR_FAN_CONFIG.
BIT BIT NAME MEANING
7:5 RAMP[2:0]
The RAMP bits select how fast the device ramps the PWM from one duty cycle to another (either up
or down). In PWM mode, the following table always applies. In RPM mode, the fan speed is read
either every 200ms or 1000ms and when the reported fan speed is within 20% of the target speed,
the maximum allowed PWM duty cycle change is set to 1%. In RPM mode, the PWM duty cycle is
not changed as long as the fan is within Q5% of the target speed.
RAMP2 RAMP1 RAMP0
PWM DUTY
CYCLE UPDATE
RATE (ms)
MAX PWM DUTY
CYCLE CHANGE
ALLOWED (%)
TIME TO RAMP
FROM 40% TO
100% PWM DUTY
CYCLE (seconds)
0 0 0 1000 1 60
0 0 1 1000 2 30
0 1 0 1000 3 20
0 1 1 200 1 12
1 0 0 200 2 6
1 0 1 200 3 4
1 1 0 200 4 3
1 1 1 200 5 2.4
4 HEALTH
The HEALTH bit controls the automatic checking of the fan health. The fan-health diagnostic can
be enabled by setting this bit to 1.
0 = Health meter function is disabled.
1 = Health meter function is enabled.
3 ROTOR_HI_LO
Determines if a locked rotor indication is active low or active high. This bit is ignored if
ROTOR = 0.
0 = ROTOR is active low (TACH input is low if the rotor stops).
1 = ROTOR is active high (TACH input is high if the rotor stops).
2 ROTOR
The ROTOR bit selects if the fan does not have a tachometer but rather a stalled (or locked)
rotor output.
ROTOR FAN OUTPUT MAX31785 CONFIGURATION
0 Tachometer TACH input expects fan RPM
1Stalled/locked rotor
detect
TACH input expects locked rotor signal. The polarity is
selected with the ROTOR_HI_LO bit (also set
MFR_FAN_FAULT_LIMIT = 0001h).
1:0 SPIN[1:0]
The SPIN bits determine how the device spins up (or starts) the fan from a dead stop. To over-
come the initial mechanical fan inertia, the device can be programmed to drive the fan at 100%
duty cycle until a programmable number of fan revolutions (cumulative count) is detected or a
locked rotor signal is negated. The device allows a 2s startup period during which the fan speed
monitors are disabled. If after 2s the fan does not respond, the PWM output remains at 100%
duty cycle (if TACHO = 0) or goes to 0% duty cycle (if TACHO = 1).
SPIN1 SPIN0 SPIN-UP RELAXATION CRITERIA
0 0 Automatic spin-up disabled
0 1 Two revolutions or locked rotor negated
1 0 Four revolutions or locked rotor negated
1 1 Eight revolutions or locked rotor negated
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MFR_FAN_LUT (F2h)
The MFR_FAN_LUT command is used to configure the LUT that controls the fan. The fan has an LUT that maps eight
programmable temperature levels to eight programmable fan PWM duty-cycle levels (bit 6 in FAN_CONFIG_1_2 is
zero) or eight programmable target fan speeds (bit 6 in FAN_CONFIG_1_2 is one). The LUT allows a wide variety of
profiles to be used.
USER NOTE: The programmable configuration of MFR_FAN_LUT must be monotonic.
Table 27. MFR_FAN_LUT
TEMPERATURE STEP: Temperature Level Setting
The TEMPERATURE STEP sets the temperature in degrees Celsius and represents a threshold level at which the
device updates the fan PWM duty cycle setting. The 2 data bytes are in DIRECT format. The valid temperature range
depends on the temperature sensor.
Table 28. Valid Temperature Range
BYTE NUMBER WORD NAME MEANING
0-1 TEMP STEP 0 Temperature for step 0.
2-3 SPEED STEP 0 Fan PWM duty cycle or fan speed for step 0.
4-5 TEMP STEP 1 Temperature for step 1.
6-7 SPEED STEP 1 Fan PWM duty cycle or fan speed for step 1.
8-9 TEMP STEP 2 Temperature for step 2.
10-11 SPEED STEP 2 Fan PWM duty cycle or fan speed for step 2.
12-13 TEMP STEP 3 Temperature for step 3.
14-15 SPEED STEP 3 Fan PWM duty cycle or fan speed for step 3.
16-17 TEMP STEP 4 Temperature for step 4.
18-19 SPEED STEP 4 Fan PWM duty cycle or fan speed for step 4.
20-21 TEMP STEP 5 Temperature for step 5.
22-23 SPEED STEP 5 Fan PWM duty cycle or fan speed for step 5.
24-25 TEMP STEP 6 Temperature for step 6.
26-27 SPEED STEP 6 Fan PWM duty cycle or fan speed for step 6.
28-29 TEMP STEP 7 Temperature for step 7.
30-31 SPEED STEP 7 Fan PWM duty cycle or fan speed for step 7.
TEMPERATURE SENSOR VALID RANGE
Page 12: Internal Temp Sensor -40NC to +85NC
Pages 13 to 16: I2C Remote Temp Sensor -55NC to +125NC
Page 6 to 11: Remote Thermal Diode Temp Sensor -40NC to +120NC
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Figure 6. Fan Lookup Table (LUT) Format
FAN SPEED STEP: Fan PWM Duty Cycle or Fan Speed Setting
If bit 6 in FAN_CONFIG_1_2 is set to zero, the FAN SPEED STEP sets the fan PWM duty cycle at each temperature step
breakpoint. The valid duty cycle range is 0 to 100 (inclusive). Any values greater than 100 (decimal) result in 100% PWM
duty cycle being generated, and any values less than 0 (decimal) result in 0% PWM duty cycle.
If bit 6 in FAN_CONFIG_1_2 is set to 1, the FAN SPEED STEP sets the fan target speed (in RPM) at each temperature
step breakpoint. The valid fan speed range is 0 to 32,767 (inclusive).
NORMALIZED TEMPERATURE
(FROM ONE OR MORE TEMP SENSORS)
S0
S1
S2
S3
S4
S5
S6
S7
MAXIMUM
DESIRED FAN
DUTY CYCLE
OR SPEED
FAN PWM DUTY CYCLE
OR
FAN SPEED (IN RPM)
PWM = 0% DUTY CYCLE
T0 T1 T2 T3 T4 T5 T6 T7
THERMAL
HYSTERESIS
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MFR_READ_FAN_PWM (F3h)
The MFR_READ_FAN_PWM command returns the latest real-time value for the fan PWM in % duty cycle.
MFR_READ_FAN_PWM is updated whenever the PWM duty cycle is updated. This is determined by the RATE bits in
MFR_FAN_CONFIG. The 2 data bytes are in DIRECT format.
MFR_FAN_FAULT_LIMIT (F5h)
The MFR_FAN_FAULT_LIMIT command sets the value of the fan speed (in RPM) or percentage of target fan speed that
causes a fan fault. Fans operating below these limits for over 10s continuous trip the fault. When the fan is operating in
RPM mode, the 10s checking period starts after the device has completed a PWM ramp of the fan speed.
The slowest tachometer signal the device can measure for a fan is 60 RPM. In dual tachometer applications, the slow-
est RPM is 360. Tachometer signals slower than these minimums are reported as 0 RPM. Fault and warning limits
should be set to RPM values greater than these minimum RPM limits.
The 2 data bytes are in DIRECT format. Set to 0000h to disable the limit checking. Set to 0001h to only alarm when the
tachometer input is locked for greater than 10s (this mode should be used when the fan only has a locked rotor output). In
response to violation of the MFR_FAN_FAULT_LIMIT or if a stalled/locked rotor is detected, the device does the following:
1) Sets the NONE OF THE ABOVE bit in STATUS_BYTE.
2) Sets the NONE OF THE ABOVE and FANS bits in STATUS_WORD.
3) Sets the FAN_1_FAULT bit in STATUS_FANS_1_2.
4) Responds as specified in the MFR_FAULT_RESPONSE.
5) Notifies the host using ALERT assertion (if enabled in MFR_MODE).
USER NOTE: For proper fan operation, MFR_FAN_FAULT_LIMIT must be configured.
MFR_FAN_WARN_LIMIT (F6h)
The MFR_FAN_WARN_LIMIT command sets the value of the fan speed (in RPM) or percentage of target fan speed that
causes a fan speed warning. Fans operating below these limits for over 10s continuous trip the warning. When the fan is
operating in RPM mode, the 10s checking period starts after the device has completed a PWM ramp of the fan speed.
Normally, the MFR_FAN_WARN_LIMIT is set higher than the MFR_FAN_FAULT_LIMIT. The 2 data bytes are in DIRECT
format. Set to 0000h to disable the limit checking. Set to 0001h to generate a warning when using a locked rotor fan.
In response to violation of the MFR_FAN_WARN_LIMIT, the device does the following:
1) Sets the NONE OF THE ABOVE bit in STATUS_BYTE.
2) Sets the NONE OF THE ABOVE and FANS bits in STATUS_WORD.
3) Sets the FAN_1_WARN bit in STATUS_FANS_1_2.
4) Notifies the host using ALERT assertion (if enabled in MFR_MODE).
Table 29. Monitored Fan Fault and Warning Parameters
FAN CONTROL MODE LIMIT PARAMETER
HYSTERESIS FOR
CLEARING THE FAULT/
WARNING
COMPARISON INTERVAL
Manual PWM Fan speed (in RPM) > (limit x 110%) Checked once a second
Manual RPM Percentage of programmed
target fan speed > (limit + 5%) Checked once a second
Automatic PWM Fan speed (in RPM) > (limit x 110%) Checked once a second
Automatic RPM Percentage of LUT target fan
speed > (limit + 5%) Checked once a second
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Table 30. MFR_FAN_PWM2RPM
MFR_FAN_RUN_TIME (F7h)
The MFR_FAN_RUN_TIME command returns the number of hours of fan lifetime operation. Once every hour, the device
automatically stores this counter in flash memory. The counter is a 16-bit value that rolls over. The latest stored value
is automatically recalled from flash memory upon device power cycle or RST action or a soft reset. This count can be
reset to zero by writing a sequence of all zeros (0000h), followed by all ones (FFFFh), followed by all zeros (0000h)
within 8ms. This value is not updated when the fan is turned off (0% PWM duty cycle).
MFR_FAN_PWM_AVG (F8h)
The MFR_FAN_PWM_AVG command returns the lifetime average of the fan PWM duty cycle in % duty cycle. This aver-
age is not updated when the fan is turned off (0% PWM duty cycle). When combined with the MFR_FAN_RUN_TIME
information, this duty cycle helps predict the remaining lifetime of the fan. Once every hour, the device automatically
stores this value in flash memory. The 2 data bytes are in DIRECT format. The latest stored value is automatically
recalled from flash memory upon device power cycle or RST action or a soft reset. This count can be reset to zero by
writing a sequence of all zeros (0000h), followed by all ones (FFFFh), followed by all zeros (0000h) within 8ms.
MFR_FAN_PWM2RPM (F9h)
The MFR_FAN_PWM2RPM command is used to configure the table the device uses to drive the fan-health status bits in
the lower nibble of STATUS_FAN_1_2. The table maps four preassigned PWM duty cycles to the expected fan speed
in RPM. Table 30 describes the MFR_FAN_PWM2RPM command.
RPM@PWM: Expected Fan Speed at a Certain PWM Duty Cycle: The expected fan speed at four PWM duty cycles
is used to determine the fan health. The fan speed is set in RPM at each PWM duty-cycle step breakpoint. The valid
fan-speed range is 0 to 32,767 (inclusive). The 2 data bytes are in DIRECT format.
Applications Information
Power-Supply Decoupling
To achieve the best results when using the device,
decouple the VDD power supply with a 0.1FF capacitor.
Use a high-quality, ceramic, surface-mount capacitor
if possible. Surface-mount components minimize lead
inductance, which improves performance, and ceram-
ic capacitors tend to have adequate high-frequency
response for decoupling applications.
Decouple the REG25 and REG18 regulator outputs using
1FF and 10nF capacitors (one each per output).
Open-Drain Pins
MSDA, MSCL, SCL, SDA, FAULT, and ALERT are open-
drain pins and require external pullup resistors con-
nected to VDD to realize high logic levels.
BYTE NUMBER WORD NAME MEANING
6-7 RPM@100% PWM Expected fan speed for a PWM duty cycle of 100%.
4-5 RPM@80% PWM Expected fan speed for a PWM duty cycle of 80%.
2-3 RPM@60% PWM Expected fan speed for a PWM duty cycle of 60%.
0-1 RPM@40% PWM Expected fan speed for a PWM duty cycle of 40%.
6-Channel Intelligent Fan Controller
MAX31785
47
Package Information
For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”,
or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
Typical Operating Circuit
PWM0
MSDA
MSCL
+3.3V
VDD
VSS
SDA
SCL
6 CHANNELS
UP TO 4
CHANNELS
TACH0
RS+0
RS-0
PWM1
TACH1
RS+1
RS-1
PWM2
TACH2
RS+2
RS-2
PWM3
TACH3
RS+3
RS-3
PWM4
TACH4
RS+4
RS-4
PWM5
TACH5
RS+5
RS-5
REMOTE
TEMPERATURE
DIODE
EACH CHANNEL
CAN READ A REMOTE
TEMPERATURE DIODE
OR A REMOTE VOLTAGE
REMOTE
VOLTAGE
RST
ALERT
FAULT
A0
HOST
INTERFACE
I2C TEMP
SENSOR
CONTROL
REG18
A1/TACHSEL
REG25
MAX31785
DS75LV SPDT
MUX
FROM
TACHSEL
OPTIONAL
SUPPORT FOR
TWO FANS
PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
40 TQFN-EP T4066+2 21-0141 90-0053
6-Channel Intelligent Fan Controller
MAX31785
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.
Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical
Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
48 Maxim Integrated Products, Inc. 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
© 2012 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 12/10 Initial release —
1 11/11
Updated the lead temperature in the Absolute Maximum Ratings section, VIL(MIN) and
VI2C_IL(MIN) values in the Recommended Operating Conditions, INL (MAX) value in
the DC Electrical Characteristics, and page numbers in Table 6
6, 7, 21
2 1/12 Added Note 4 to the INL parameter and removed the DNL parameter in the DC
Electrical Characteristics 7, 8
3 8/12
Added Note 5 to the tBUF parameter conditions and changed tBUF(MIN) from 4.7µs to
1.4ms in the I2C/SMBus Interface Electrical Characteristics; added statement about
not sending another command for at least 250ms to the STORE_DEFAULT_ALL (11h),
RESTORE_DEFAULT_ALL (12h), and MFR_MODE (D1h) command sections
8, 28, 35
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