MAX6581TG98+T - Maxim - Datasheet.Live

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±1°C Accurate 8-Channel Temperature Sensor

MAX6581

19-5260; Rev 0; 8/10

Ordering Information/Selector Guide

General Description

The MAX6581 precision multichannel temperature

sensor monitors its own temperature and the tempera-

tures of up to seven external diode-connected transis-

tors. All temperature channels have programmable alert

and overtemperature thresholds. When the measured

temperature of a channel crosses the respective thresh-

old, a status bit is set in one of the status registers. Two

open-drain alarm outputs (ALERT and OVERT) assert

corresponding to these bits in the status register(s).

Resistance cancellation is available for all channels and

compensates for high series resistance in circuit-board

traces and thermal diodes.

The 2-wire serial interface accepts SMBus™ protocols

(write byte, read byte, send byte, and receive byte) for

reading the temperature data and programming the

alarm thresholds.

The MAX6581 is specified for an operating temperature

range of -40NC to +125NC and is available in a 24-pin,

4mm x 4mm thin QFN package with an exposed pad.

Features

S Eight Channels to Measure Seven Remote and

One Local Temperature

S 11-Bit, 0.125NC Resolution

S High Accuracy of ±1NC (max) from +60NC to

+100NC (Remote Channels)

S -64NC to +150NC Remote Temperature Range

S Programmable Undertemperature/

Overtemperature Alerts

S SMBus/I2C-Compatible Interface

S Two Open-Drain Alarm Outputs (ALERT and

OVERT)

S Resistance Cancellation on All Remote Channels

Applications

Desktop Computers

Notebook Computers

Workstations

Servers

Data Communications

SMBus is a trademark of Intel Corp.

+Denotes a lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad.

**Future product—contact factory for availability.

Note: These devices operate over the -40NC to +125NC operating temperature range.

Typical Application Circuit appears at end of data sheet.

EVALUATION KIT

AVAILABLE

PART SLAVE ADDRESS PIN-PACKAGE OPERATING

TEMPERATURE RANGE

MEASURED

TEMPERATURE RANGE

MAX6581TG9A+ 0X9A 24 TQFN-EP* -40NC to +125NC -64NC to +150NC

MAX6581TG9C+** 0X9C 24 TQFN-EP* -40NC to +125NC -64NC to +150NC

MAX6581TG9E+** 0X9E 24 TQFN-EP* -40NC to +125NC -64NC to +150NC

MAX6581TG98+** 0X98 24 TQFN-EP* -40NC to +125NC -64NC to +150NC

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

2 ______________________________________________________________________________________

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.

(All Voltages Referenced to GND)

VCC, SMBCLK, SMBDATA, ALERT,

OVERT, STBY to GND ..........................................-0.3V to +4V

DXP_ to GND ............................................ -0.3V to (VCC + 0.3V)

DXN_ to GND ........................................... -0.3V to (VCC + 0.3V)

SMBDATA, ALERT, OVERT Current .................. -1mA to +50mA

DXN_ Current .................................................................... Q1mA

Continuous Power Dissipation (TA = +70NC)

24-Pin Thin QFN (derate 27.8mW/NC above +70NC) .. 2222mW

Package Junction-to-Ambient Thermal Resistance

(BJA) (Note 1) ............................................................36.0NC/W

Package Junction-to-Case Thermal Resistance

(BJC) (Note 1) ..............................................................3.0NC/W

ESD Protection (all pins, Human Body Model) ...................Q2kV

Operating Temperature Range ........................ -40NC to +125NC

Junction Temperature .....................................................+150NC

Storage Temperature Range .......................... -65NC to +150NC

Lead Temperature (soldering, 10s) ...............................+300NC

Soldering Temperature (reflow) ......................................+260NC

ELECTRICAL CHARACTERISTICS

(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Note 2)

ABSOLUTE MAXIMUM RATINGS

Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-

layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage VCC 3.0 3.6 V

Standby Supply Current ISS SMBus static 4 15 FA

Operating Current ICC1 During conversion, RC off 500 600 FA

ICC2 During conversion, RC on 550 650

Temperature Resolution 11 Bits

0.125 NC

3-Sigma Temperature Accuracy

(Remote Channels 1–7) VCC = 3.3V

TA = +30NC to +85NC,

TRJ = +60NC to +100NC-0.85 +0.85

NCTA, TRJ = -40NC to +125NC-1.2 +1.2

TA = +30NC to +85NC,

TRJ = +100NC to +150NC-2.5 +2.5

3-Sigma Temperature Accuracy

(Local) VCC = 3.3V

TA = +30NC to +85NC-1 +1

NCTA = -40NC to +125NC-2 +2

TA = 0NC to +150NC-3 +3

6-Sigma Temperature Accuracy

(Remote Channels 1–7) VCC = 3.3V

TA = +30NC to +85NC,

TRJ = +60NC to +100NC-1 +1

NCTA, TRJ = -40NC to +125NC-2 +2

TA = +30NC to +85NC,

TRJ = +100NC to +125NC-2.75 +2.75

6-Sigma Temperature Accuracy

(Local) VCC = 3.3V

TA = +30NC to +85NC-1.5 +1.5

NCTA = -40NC to +125NC-2.5 +2.5

TA = 0NC to +150NC-3.5 +3.5

Supply Sensitivity of

Temperature Accuracy Q0.2 NC/V

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Note 2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Conversion Time per Channel tCONV

Resistance cancellation mode off 95 125 156

Resistance cancellation mode on or beta

compensation on 190 250 312

Remote-Diode Source Current IRJ

High level Resistance cancellation

mode off

80 100 120

Low level 8 10 12

High level Resistance cancellation

mode on or beta

compensation on

160 200 240

Low level 16 20 24

DXP_ and DXN_ Leakage

Current Standby mode 100 nA

Undervoltage Lockout Threshold UVLO Falling edge of VCC disables ADC 2.25 2.80 2.95 V

Undervoltage Lockout Hysteresis 90 mV

Power-On-Reset (POR)

Threshold VCC falling edge 1.3 2.0 2.2 V

POR Threshold Hysteresis 90 mV

ALERT and OVERT

Output Low Voltage VOL ISINK = 1mA 0.01 V

ISINK = 6mA 0.3

Input Leakage Current ILEAK -1 +1 FA

SMBus INTERFACE, STBY

Logic Input Low Voltage VIL VCC = 3.6V 0.8 V

Logic Input High Voltage VIH VCC = 3.0V 2.2 V

Input Leakage Current -1 +1 FA

Output Low Voltage VOL ISINK = 6mA 0.1 V

Input Capacitance CIN 5 pF

SMBus-COMPATIBLE TIMING (Figures 3 and 4) (Note 3)

Serial-Clock Frequency fSMBCLK (Note 4) 400 kHz

Bus Free Time Between STOP

and START Condition tBUF fSMBCLK = 400kHz 1.6 Fs

START Condition Setup Time fSMBCLK = 400kHz 0.6 Fs

Repeated START Condition

Setup Time tSU:STA 90% of SMBCLK to 90% of SMBDATA,

fSMBCLK = 400kHz 50 ns

START Condition Hold Time tHD:STA 10% of SMBDATA to 90% of SMBCLK,

fSMBCLK = 400kHz 0.6 Fs

STOP Condition Setup Time tSU:STO 90% of SMBCLK to 90% of SMBDATA,

fSMBCLK = 400kHz 0.6 Fs

Clock Low Period tLOW 10% to 10%, fSMBCLK = 400kHz 1 Fs

Clock High Period tHIGH 90% to 90% 0.6 Fs

Data-In Hold Time tHD:DAT 0 0.9 us

Data-In Setup Time tSU:DAT (Note 5) 100 ns

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

4 ______________________________________________________________________________________

Typical Operating Characteristics

(VCC = +3.3V, VSTBY = VCC, TA = +25NC, unless otherwise noted.)

ELECTRICAL CHARACTERISTICS (continued)

(VCC = +3.0V to +3.6V, TA = -40NC to +125NC, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25NC.) (Note 2)

Note 2: All parameters are tested at TA = +85NC. Specifications over temperature are guaranteed by design.

Note 3: Timing specifications are guaranteed by design.

Note 4: The serial interface resets when SMBCLK is low for more than tTIMEOUT.

Note 5: A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SMBCLK’s falling

edge.

STANDBY SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX6581 toc01

SUPPLY VOLTAGE (V)

STANDBY SUPPLY CURRENT (µA)

3.53.43.33.23.1

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

3.0 3.6

HARDWARE OR SOFTWARE

STANDBY SUPPLY CURRENT

AVERAGE OPERATING SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX6581 toc02

SUPPLY VOLTAGE (V)

AVERAGE OPERATING SUPPLY CURRENT (µA)

3.53.43.1 3.2 3.3

365

370

375

380

385

390

395

400

360

3.0 3.6

RESISTANCE

CANCELLATION OFF

REMOTE-DIODE TEMPERATURE ERROR

vs. REMODE-DIODE TEMPERATURE

MAX6581 toc03

REMOTE-DIODE TEMPERATURE (°C)

REMOTE-DIODE TEMPERATURE ERROR (°C)

1109050 703010

-3

-2

-1

-4

-5

-6

-7

-8

-9

-10 -10 130

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Receive SMBCLK/SMBDATA

Rise Time tR300 ns

Receive SMBCLK/SMBDATA Fall

Time tF300 ns

Data-Out Hold Time tDH 50 ns

Pulse Width of Spike Suppressed tSP 0 50 ns

SMBus Timeout tTIMEOUT SMBDATA low period for interface reset 25 37 45 ms

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

_______________________________________________________________________________________ 5

Typical Operating Characteristics (continued)

(VCC = +3.3V, VSTBY = VCC, TA = +25NC, unless otherwise noted.)

LOCAL TEMPERATURE ERROR

vs. DIE TEMPERATURE

MAX6581 toc04

DIE TEMPERATURE (°C)

LOCAL TEMPERATURE ERROR (°C)

908060 7010 20 30 40 500

-4

-3

-2

-1

-5

-10 100

REMOTE-DIODE TEMPERATURE ERROR

vs. POWER-SUPPLY NOISE FREQUENCY

MAX6581 toc05

POWER-SUPPLY NOISE FREQUENCY (MHz)

REMOTE-DIODE TEMPERATURE ERROR (°C)

10.10.01

-4

-3

-2

-1

-5

0.001 10

100mVP-P

TRJ = +85°C

LOCAL TEMPERATURE ERROR

vs. POWER-SUPPLY NOISE FREQUENCY

MAX6581 toc06

POWER-SUPPLY NOISE FREQUENCY (MHz)

LOCAL TEMPERATURE ERROR (°C)

10.10.01

-4

-3

-2

-1

-5

0.001 10

100mVP-P

REMOTE-DIODE TEMPERATURE ERROR

vs. CAPACITANCE

MAX6581 toc07

CAPACITANCE (nF)

REMOTE-DIODE TEMPERATURE ERROR (°C)

-4

-3

-2

-1

-5

1 100

100mVP-P

TRJ = +85°C

REMOTE-DIODE TEMPERATURE ERROR

vs. RESISTANCE

MAX6581 toc08

RESISTANCE (I)

REMOTE-DIODE TEMPERATURE ERROR (°C)

908060 7020 30 40 5010

-5

0 100

TRJ = +85°C

RESISTANCE

CANCELLATION OFF

RESISTANCE

CANCELLATION ON

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

6 ______________________________________________________________________________________

Pin Configuration

Pin Description

PIN NAME FUNCTION

1 DXP2

Combined Current Source and ADC Positive Input for Channel 2 Remote Diode. Connect DXP2 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP2 unconnected

or connect to DXN2 if a remote diode is not used. Connect a 100pF capacitor between DXP2 and

DXN2 for noise filtering.

2 DXN2

Cathode Input for Channel 2 Remote Diode. Connect the cathode of the channel 2 remote-diode-

connected transistor to DXN2. If the channel 2 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN2. Leave DXN2 unconnected or connect to DXP2 if a

remote diode is not used. Connect a 100pF capacitor between DXP2 and DXN2 for noise filtering.

3 DXP3

Combined Current Source and ADC Positive Input for Channel 3 Remote Diode. Connect DXP3 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP3 unconnected

or connect to DXN3 if a remote diode is not used. Connect a 100pF capacitor between DXP3 and

DXN3 for noise filtering.

4 DXN3

Cathode Input for Channel 3 Remote Diode. Connect the cathode of the channel 3 remote-diode-

connected transistor to DXN3. If the channel 3 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN3. Leave DXN3 unconnected or connect to DXP3 if a

remote diode is not used. Connect a 100pF capacitor between DXP3 and DXN3 for noise filtering.

5 DXP4

Combined Current Source and ADC Positive Input for Channel 4 Remote Diode. Connect DXP4 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP4 unconnected

or connect to DXN4 if a remote diode is not used. Connect a 100pF capacitor between DXP4 and

DXN4 for noise filtering.

6, 22 N.C. No Connection. Connect to other N.C. or leave unconnected.

DXN2

DXN3

DXP4

N.C.

DXP2

VCC

I.C.

STBY

ALERT

DXP7

1 2

N.C.

4 5 6

1718 16 14 13

DXP1

DXN1

DXN6

DXN5

DXP5

DXN4

MAX6581

DXP3 OVERT

GND

20 11 DXP6

SMBCLK

19 12 DXN7

SMBDATA

TOP VIEW

*EP = EXPOSED PAD, CONNECT TO GND

*EP

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

_______________________________________________________________________________________ 7

Pin Description (continued)

PIN NAME FUNCTION

7 DXN4

Cathode Input for Channel 4 Remote Diode. Connect the cathode of the channel 4 remote-diode-

connected transistor to DXN4. If the channel 4 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN4. Leave DXN4 unconnected or connect to DXP4 if a

remote diode is not used. Connect a 100pF capacitor between DXP4 and DXN4 for noise filtering.

8 DXP5

Combined Current Source and ADC Positive Input for Channel 5 Remote Diode. Connect DXP5 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP5 unconnected

or connect to DXN5 if a remote diode is not used. Connect a 100pF capacitor between DXP5 and

DXN5 for noise filtering.

9 DXN5

Cathode Input for Channel 5 Remote Diode. Connect the cathode of the channel 5 remote-diode-

connected transistor to DXN5. If the channel 5 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN5. Leave DXN5 unconnected or connect to DXP5 if a

remote diode is not used. Connect a 100pF capacitor between DXP5 and DXN5 for noise filtering.

10 DXN6

Cathode Input for Channel 6 Remote Diode. Connect the cathode of the channel 6 remote-diode-

connected transistor to DXN6. If the channel 6 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN6. Leave DXN6 unconnected or connect to DXP6 if a

remote diode is not used. Connect a 100pF capacitor between DXP6 and DXN6 for noise filtering.

11 DXP6

Combined Current Source and ADC Positive Input for Channel 6 Remote Diode. Connect DXP6 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP6 unconnected

or connect to DXN6 if a remote diode is not used. Connect a 100pF capacitor between DXP6 and

DXN6 for noise filtering.

12 DXN7

Cathode Input for Channel 7 Remote Diode. Connect the cathode of the channel 7 remote-diode-

connected transistor to DXN7. If the channel 7 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN7. Leave DXN7 unconnected or connect to DXP7 if a

remote diode is not used. Connect a 100pF capacitor between DXP7 and DXN7 for noise filtering.

13 DXP7

Combined Current Source and ADC Positive Input for Channel 7 Remote Diode. Connect DXP7 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP7 unconnected

or connect to DXN7 if a remote diode is not used. Place a 100pF capacitor between DXP7 and

DXN7 for noise filtering.

14 STBY Active-Low Standby Input. Drive STBY logic-low to place the MAX6581 in standby mode, or logic-

high for normal mode. Temperature and threshold data are retained in standby mode.

15 I.C. Internally Connected. I.C. is internally connected to VCC. Connect I.C. to VCC or leave unconnected.

16 OVERT Overtemperature Active-Low, Open-Drain Output. OVERT asserts low when the temperature of any

remote channel exceeds the programmed threshold limit.

17 VCC Supply Voltage Input. Bypass to GND with a 0.1FF capacitor.

18 ALERT SMBus Alert (Interrupt), Active-Low, Open-Drain Output. ALERT asserts low when the temperature of

any channel crosses a programmed ALERT high or low threshold.

19 SMBDATA SMBus Serial-Data Input/Output. Connect SMBDATA to a pullup resistor.

20 SMBCLK SMBus Serial-Clock Input. Connect SMBCLK to a pullup resistor.

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

8 ______________________________________________________________________________________

Detailed Description

The MAX6581 is a precision multichannel temperature

monitor that features one local and seven remote tem-

perature-sensing channels with a programmable alert

threshold for each temperature channel and a program-

mable overtemperature threshold for channels 1–7 (see

Figure 1). Communication with the MAX6581 is achieved

through the SMBus serial interface and a dedicated alert

pin (ALERT). The alarm outputs, (OVERT and ALERT)

assert if the software-programmed temperature thresh-

olds are exceeded. ALERT also asserts if the measured

temperature falls below the ALERT low limits. ALERT

typically serves as an interrupt, while OVERT can be

connected to a fan, system shutdown, or other thermal-

management circuitry.

ADC Conversion Sequence

The MAX6581 starts the conversion sequence by

measuring the temperature on channel 1, followed by 2,

local channel, 3–7. The conversion result for each active

channel is stored in the corresponding temperature data

does not have a diode.

Low-Power Standby Mode

Enter software-standby mode by setting the STOP

bit to 1 in the Configuration register. Enter hardware-

standby by pulling STBY low. Software-standby mode

disables the ADC and reduces the supply current to

approximately 4FA. During either software or hardware

standby, data is retained in memory. During hardware

standby, the SMBus interface is inactive. During software

standby, the SMBus interface is active and listening for

commands. The timeout is enabled if a START condition

is recognized on SMBus. Activity on the SMBus causes

the supply current to increase. If a standby command is

received while a conversion is in progress, the conver-

sion cycle is interrupted, and the temperature registers

are not updated. The previous data is not changed and

remains available.

Operating-Current Calculation

The MAX6581 operates at different operating-current

levels depending on how many external channels are in

use and how many of those are in resistance cancella-

tion (RC) mode. The average operating current is:

N R

AV CC1 CC2

N R N R

N 1 2 N

I I I

N 2 N 1 N 2 N 1

+ ×

= + ×

+ × + + × +

where:

NN = the number of remote channels that are operating

in normal mode.

NR = the number of remote channels that are in RC

mode.

IAV = the average operating power-supply current over a

complete series of conversions.

ICC1 = the average operating power-supply current

during a conversion in normal mode.

ICC2 = the average operating power-supply current

during a conversion in RC mode.

Pin Description (continued)

PIN NAME FUNCTION

21 GND Ground

23 DXP1

Combined Current Source and ADC Positive Input for Channel 1 Remote Diode. Connect DXP1 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP1 unconnected

or connect to DXN1 if a remote diode is not used. Connect a 100pF capacitor between DXP1 and

DXN1 for noise filtering.

24 DXN1

Cathode Input for Channel 1 Remote Diode. Connect the cathode of the channel 1 remote-diode-

connected transistor to DXN1. If the channel 1 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN1. Leave DXN1 unconnected or connect to DXP1 if a

remote diode is not used. Connect a 100pF capacitor between DXP1 and DXN1 for noise filtering.

— EP Exposed Pad. Connect EP to GND.

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

_______________________________________________________________________________________ 9

Figure 1. Internal Block Diagram

VCC

DXN2

DXP2

DXN1

DXP1

DXN3

DXP3

DXN4

DXP4

DXN5

DXP5

DXN6

DXP6

LOCAL

TRANSISTOR

SMBCLK SMBDATA

INPUT

BUFFER

REF

COUNTER

SMBus INTERFACE

COUNT

DXN7

DXP7

IRJ

COMMAND BYTE

REMOTE TEMPERATURES

LOCAL TEMPERATURES

STBY

OVERT

ALERT THRESHOLD

OVERT THRESHOLD

ALERT RESPONSE ADDRESS

ALERT

ALARM

ALU

MAX6581

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

10 _____________________________________________________________________________________

SMBus Digital Interface

From a software perspective, the MAX6581 appears

as a series of 8-bit registers that contain temperature-

measurement data, alarm threshold values, and control

bits. A standard SMBus-compatible, 2-wire serial inter-

face is used to read temperature data and write control

bits and alarm threshold data. The same SMBus slave

address also provides access to all functions.

The MAX6581 employs four standard SMBus proto-

cols: write byte, read byte, send byte, and receive byte

(Figure 2). The shorter receive-byte protocol allows

quicker transfers, provided that the correct data regis-

ter was previously selected by a read-byte instruction.

Use caution with the shorter protocols in multimaster

systems, since a second master could overwrite the

command byte without informing the first master. Figure

3 is the SMBus write timing diagram and Figure 4 is the

SMBus read timing diagram.

The remote-diode-measurement channels provide

11 bits of data (1 LSB = 0.125NC). The eight most

significant bits (MSBs) can be read from the local tem-

perature and remote temperature registers. The remain-

ing 3 bits for remote can be read from the extended

temperature register. If extended resolution is desired,

the extended-resolution register should be read first.

This prevents the MSBs from being overwritten by new

conversion results until they have been read. If the MSBs

have not been read within a SMBus timeout period (nom-

inally 37ms), normal updating continues. Table 1 shows

the main temperature register (high-byte) data format

and Table 2 shows the extended-resolution register (low-

byte) data format.

Figure 2. SMBus Protocols

S ADDRESS WR ACK ACK PDATA ACKCOMMAND

7 BITS 18 BITS8 BITS

SLAVE ADDRESS: EQUIVALENT

TO CHIP-SELECT LINE OF

A 3-WIRE INTERFACE

DATA BYTE: DATA GOES INTO THE REGISTER

SET BY THE COMMAND BYTE (TO SET

THRESHOLDS, CONFIGURATION MASKS, AND

SAMPLING RATE)

WRITE-BYTE FORMAT

S ADDRESSADDRESS WR ACK ACK PS RD ACK ///DATACOMMAND

7 BITS 7 BITS 8 BITS8 BITS

READ-BYTE FORMAT

SLAVE ADDRESS: EQUIVALENT

TO CHIP SELECT LINE

COMMAND BYTE: SELECTS

WHICH REGISTER YOU ARE

READING FROM

S PADDRESS WR ACK ACKCOMMAND

7 BITS 8 BITS

SEND-BYTE FORMAT

COMMAND BYTE: SENDS COMMAND

WITH NO DATA, USUALLY

USED FOR ONE-SHOT COMMAND

S PADDRESS RD ACK ///DATA

7 BITS 8 BITS

RECEIVE-BYTE FORMAT

DATA BYTE: READS DATA FROM

THE REGISTER COMMANDED

BY THE LAST READ-BYTE OR

WRITE-BYTE TRANSMISSION;

ALSO USED FOR SMBus ALERT

RESPONSE RETURN ADDRESS

SLAVE ADDRESS: REPEATED

DUE TO CHANGE IN DATA-

FLOW DIRECTION

DATA BYTE: READS FROM

THE REGISTER SET BY THE

COMMAND BYTE

S = START CONDITION

P = STOP CONDITION

SHADED = SLAVE TRANSMISSION

/// = NOT ACKNOWLEDGED

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

______________________________________________________________________________________ 11

Figure 3. SMBus Write Timing Diagram

Figure 4. Read-Timing Diagram

Table 1. Main Temperature Register (High-Byte) Data Format

SMBCLK

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

A B C D EF G H I J

SMBDATA

tSU:STA tHD:STA

tLOW tHIGH

tSU:DAT tSU:STO tBUF

L MK

E = SLAVE PULLS SMBDATA LINE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO SLAVE

H = LSB OF DATA CLOCKED INTO SLAVE

I = SLAVE PULLS DATA LINE LOW

J = ACKNOWLEDGE CLOCKED INTO MASTER

K = ACKNOWLEDGE CLOCK PULSE

L = STOP CONDITION

M = NEW START CONDITION

SMBCLK

A B C D EF G H I

SMBDATA

tSU:STA tHD:STA

tLOW tHIGH

tSU:DAT tHD:DAT tSU:STO tBUF

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

E = SLAVE PULLS SMBDATA LINE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO MASTER

H = LSB OF DATA CLOCKED INTO MASTER

I = ACKNOWLEDGE CLOCK PULSE

J = STOP CONDITION

K = NEW START CONDITION

TEMPERATURE (NC) DIGITAL OUTPUT

NORMAL FORMAT EXTENDED FORMAT

Diode fault (open or short) 1111 1111 1111 1111

> +191 1111 1111 1111 1111

+191 1111 1111 1111 1111

+150 1101 0110 1100 1100

+127 1011 1111 1011 1111

+25 0101 1001 1001 1001

0 0100 0000 0100 0000

-39 0001 1001 0101 1001

-64 0000 0000 0000 0000

< -64 0000 0000 0000 0000

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

12 _____________________________________________________________________________________

Table 2. Extended-Resolution Temperature Register (Low-Byte) Data Format

Table 3. Command Byte Register Bit Assignment

X = Don’t care.

TEMPERATURE (NC) DIGITAL OUTPUT

0 000X XXXX

+0.125 001X XXXX

+0.250 010X XXXX

+0.375 011X XXXX

+0.500 100X XXXX

+0.625 101X XXXX

+0.750 110X XXXX

+0.875 111X XXXX

(HEX)

POR

VALUE

(HEX)

READ/

WRITE DESCRIPTION

Remote 1 01 00 R Read channel 1 remote temperature

Remote 2 02 00 R Read channel 2 remote temperature

Remote 3 03 00 R Read channel 3 remote temperature

Remote 4 04 00 R Read channel 4 remote temperature

Remote 5 05 00 R Read channel 5 remote temperature

Remote 6 06 00 R Read channel 6 remote temperature

Local 07 00 R Read local temperature

Remote 7 08 00 R Read channel 7 remote temperature

Remote 1 Extended

Bits* 09 00 R Read channel 1 remote-diode extended temperature

Manufacturer ID 0A 4D R Read manufacturer ID

Revision ID 0F 00 R Read revision ID

Remote 1 ALERT High

Limit 11 7F R/W Read/write channel 1 remote-diode alert high-temperature

threshold limit

Remote 2 ALERT High

Limit 12 7F R/W Read/write channel 2 remote-diode alert high-temperature

threshold limit

Remote 3 ALERT High

Limit 13 64 R/W Read/write channel 3 remote-diode alert high-temperature

threshold limit

Remote 4 ALERT High

Limit 14 64 R/W Read/write channel 4 remote-diode alert high-temperature

threshold limit

Remote 5 ALERT High

Limit 15 64 R/W Read/write channel 5 remote-diode alert high-temperature

threshold limit

Remote 6 ALERT High

Limit 16 64 R/W Read/write channel 6 remote-diode alert high-temperature

threshold limit

Local ALERT High Limit 17 5A R/W Read/write local-diode alert high-temperature threshold limit

Remote 7 ALERT High

Limit 18 64 R/W Read/write channel 7 remote-diode alert high-temperature

threshold limit

Local OVERT High Limit 20 50 R/W Read/write channel local-diode overtemperature threshold limit

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

______________________________________________________________________________________ 13

Table 3. Command Byte Register Bit Assignment (continued)

*Duplicate entries.

(HEX)

POR

VALUE

(HEX)

READ/

WRITE DESCRIPTION

Remote 1 OVERT High

Limit 21 6E R/W Read/write channel 1 remote-diode overtemperature threshold limit

Remote 2 OVERT High

Limit 22 6E R/W Read/write channel 2 remote-diode overtemperature threshold limit

Remote 3 OVERT High

Limit 23 6E R/W Read/write channel 3 remote-diode overtemperature threshold limit

Remote 4 OVERT High

Limit 24 7F R/W Read/write channel 4 remote-diode overtemperature threshold limit

Remote 5 OVERT High

Limit 25 5A R/W Read/write channel 5 remote-diode overtemperature threshold limit

Remote 6 OVERT High

Limit 26 5A R/W Read/write channel 6 remote-diode overtemperature threshold limit

Remote 7 OVERT High

Limit 27 5A R/W Read/write channel 7 remote-diode overtemperature threshold limit

ALERT Low Limits (all

channels) 30 00 R/W Read/write all channels alert low-temperature threshold limit

Configuration 41 00 R/W Read/write configuration

ALERT Mask 42 00 R/W Read/write ALERT mask

OVERT Mask 43 00 R/W Read/write OVERT mask

ALERT High Status 44 00 R Read ALERT high status

OVERT Status 45 00 R Read OVERT status

Diode Fault Status 46 00 R Read diode fault status

ALERT Low Status 47 00 R Read ALERT low status

ALERT Low Disable 48 FF R/W Read/write ALERT low disable

Resistance Cancellation 4A 00 R/W Read/write resistance cancellation enable bits (1 = On, 0 = Off)

Transistor Ideality 4B 00 R/W Read/write ideality value for remote-sense transistor

Ideality Select 4C 00 R/W Read/write ideality value selection bits (1 = selected transistor

ideality, 0 = 1.008)

Offset 4D 00 R/W Read/write temperature offset value

Offset Select 4E 00 R/W Read/write offset value selection bits (1 = value in Offset Select

Remote 1 Extended

Bits* 51 00 R Read channel 1 remote extended temperature

Remote 2 Extended Bits 52 00 R Read channel 2 remote extended temperature

Remote 3 Extended Bits 53 00 R Read channel 3 remote extended temperature

Remote 4 Extended Bits 54 00 R Read channel 4 remote extended temperature

Remote 5 Extended Bits 55 00 R Read channel 5 remote extended temperature

Remote 6 Extended Bits 56 00 R Read channel 6 remote extended temperature

Local Extended Bits 57 00 R Read local channel extended temperature

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

14 _____________________________________________________________________________________

Diode Fault Detection

If a channel’s input DXP_ and DXN_ are left open or are

shorted, the MAX6581 detects a diode fault. An open

diode fault does not cause either ALERT or OVERT to

assert. A bit in the status register for the correspond-

ing channel is set to 1 and the temperature data for the

channel is stored as all 1s (FFh). It takes approximately

4ms for the MAX6581 to detect a diode fault. Once a

diode fault is detected, the MAX6581 goes to the next

channel in the conversion sequence.

Alarm Threshold Registers

There are 17 alarm threshold registers that store over-

temperature and undertemperature ALERT and OVERT

threshold values. Nine of these registers are dedicated

to storing one local alert overtemperature threshold limit,

seven remote alert overtemperature threshold limits, and

one shared alert undertemperature temperature thresh-

old limit (see the ALERT Interrupt Mode section). The

remaining eight registers are dedicated to storing one

local overtemperature threshold limit and seven remote

channels to store overtemperature threshold limits (see

the OVERT Overtemperature Alarms section). Access to

these registers is provided through the SMBus interface.

ALERT Interrupt Mode

ALERT interrupts occur when the internal or external

temperature reading exceeds a high-temperature limit

(user programmable) or a low-temperature limit. The

ALERT interrupt output signal can be cleared by reading

the status register(s) associated with the fault(s) or by

successfully responding to an alert response address

transmission by the master. In both cases, the alert is

cleared but is reasserted at the end of the next conver-

sion if the fault condition still exists. The interrupt does

not halt automatic conversions. The ALERT output is

open-drain so that multiple devices can share a common

interrupt line. All ALERT interrupts can be masked using

the ALERT Mask register (42h). The POR state of these

registers is shown in Table 3.

ALERT Responses Address

The SMBus alert response interrupt pointer provides

quick fault identification for simple slave devices that

lack the complex logic necessary to be a bus master.

Upon receiving an interrupt signal, the host master

can broadcast a receive-byte transmission to the alert

response slave address (19h). Then, any slave device

that generated an interrupt attempts to identify itself by

putting its own address on the bus.

The alert response can activate several different slave

devices simultaneously, similar to the I2C general call.

If more than one slave attempts to respond, bus arbitra-

tion rules apply, and the device with the lower address

code wins. The losing device does not generate an

acknowledgment and continues to hold the ALERT line

low until cleared (the conditions for clearing an alert

vary depending on the type of slave device.) Successful

completion of the alert response protocol clears the out-

put latch. If the condition that caused the alert still exists,

the MAX6581 reasserts the ALERT interrupt at the end of

the next conversion.

OVERT Overtemperature Alarms

The MAX6581 has eight overtemperature registers that

store alarm threshold data for the OVERT output. OVERT

is asserted when a channel’s measured temperature

is greater than the value stored in the corresponding

threshold register. OVERT remains asserted until the

temperature drops below the programmed threshold

minus 4NC hysteresis. An overtemperature output can be

used to activate a cooling fan, send a warning, initiate

clock throttling, or trigger a system shutdown to prevent

component damage. See Table 3 for the POR state of the

overtemperature threshold registers.

Command Byte Register Functions

The 8-bit Command Byte register (Table 3) is the master

index that points to the various other registers within the

MAX6581. This register’s POR state is 0000 0000 (00h).

Configuration Register (41h)

The Configuration register (Table 4) has several

functions. Bit 7 (MSB) is used to put the MAX6581

either in software-standby mode (STOP) or continuous-

conversion mode. Bit 6 resets all registers to their POR

conditions and then clears itself. Bit 5 disables the

SMBus timeout. Bit 1 sets the extended range of the

remote temperature diodes. The remaining bits of the

Configuration register are not used. The POR state of this

ALERT Mask Register (42h)

The ALERT Mask register functions are described

in Table 5. Bits [7:0] are used to mask the ALERT

interrupt output. Bit 6 masks the local alert interrupt and

the remaining bits mask the remote alert interrupts. The

power-up state of this register is 0000 0000 (00h).

OVERT Mask Register (43h)

Table 6 describes the OVERT Mask register. Bit 6 and

the remaining bits mask the OVERT interrupt output for

all channels. The power-up state of this register is 0000

0000 (00h).

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

______________________________________________________________________________________ 15

Table 4. Configuration Register (41h)

Table 5. ALERT Mask Register (42h)

Table 6. OVERT Mask Register (43h)

BIT NAME POR

VALUE FUNCTION

7 (MSB) STOP 0 Standby-Mode Control Bit. If STOP is set to logic 1, the MAX6581 stops converting

and enters standby mode.

6 POR 0 Reset Bit. Set to logic 1 to put the device into its power-on state. This bit is self-

clearing.

5TIMEOUT 0 Timeout Enable Bit. Set to logic 0 to enable SMBus timeout.

4 RESERVED 0 Reserved. Must be set to 0.

3 RESERVED 0 Reserved. Must be set to 0.

2 RESERVED 0 Reserved. Must be set to 0.

1 EXTRANGE 0 Extended-Range Enable Bit. Set bit 1 to logic 1 to set the temperature and limit data

range to -64NC to +191NC. Set bit 1 to logic 0 to set the range to 0NC to +255NC.

0 RESERVED 0 Reserved. Must be set to 0.

BIT NAME POR

VALUE FUNCTION

7 (MSB) Mask ALERT 7 0Channel 7 Alert Mask. Set to logic 1 to mask channel 7 ALERT.

6Mask Local

ALERT 0Local Alert Mask. Set to logic 1 to mask local channel ALERT.

5Mask ALERT 6 0Channel 6 Alert Mask. Set to logic 1 to mask channel 6 ALERT.

4Mask ALERT 5 0Channel 5 Alert Mask. Set to logic 1 to mask channel 5 ALERT.

3Mask ALERT 4 0Channel 4 Alert Mask. Set to logic 1 to mask channel 4 ALERT.

2Mask ALERT 3 0Channel 3 Alert Mask. Set to logic 1 to mask channel 3 ALERT.

1Mask ALERT 2 0Channel 2 Alert Mask. Set to logic 1 to mask channel 2 ALERT.

0Mask ALERT 1 0Channel 1 Alert Mask. Set to logic 1 to mask channel 1 ALERT.

BIT NAME POR

VALUE FUNCTION

7 (MSB) Mask OVERT 7 0Channel 7 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 7 OVERT.

6Mask Local

OVERT 0Local Overt Mask. Set to logic 1 to mask local channel OVERT.

5Mask OVERT 6 0Channel 6 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 6 OVERT.

4Mask OVERT 5 0Channel 5 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 5 OVERT.

3Mask OVERT 4 0Channel 4 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 4 OVERT.

2Mask OVERT 3 0Channel 3 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 3 OVERT.

1Mask OVERT 2 0Channel 2 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 2 OVERT.

0Mask OVERT 1 0Channel 1 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 1 OVERT.

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

16 _____________________________________________________________________________________

Status Register Functions

There are four status registers (see Tables 7–10). The

ALERT High Status register indicates whether a mea-

sured local or remote temperature has exceeded the

associated threshold limit set in an ALERT High Limit

a measured temperature has exceeded the associated

threshold limit set in an OVERT High Limit register. The

Diode Fault Status register indicates whether there is a

diode fault (open or short) in any of the remote-sensing

channels. The ALERT Low Status register indicates

whether the measured temperature has fallen below the

threshold limit set in the ALERT Low Limits register for

the local or remote-sensing diodes.

Bits in the alert status registers are cleared by a success-

ful read, but set again after the next conversion unless

the fault is corrected, either by a drop in the measured

temperature or a change in the threshold temperature.

The ALERT interrupt output follows the status flag bit.

Once the ALERT output is asserted, it can be deasserted

by either reading the ALERT High Status register or by

successfully responding to an alert response address. In

both cases, the alert is cleared even if the fault condition

exists, but the ALERT output reasserts at the end of the

next conversion.

The bits indicating OVERT faults clear only when the

measured temperature drops below the temperature

threshold minus the hysteresis value (4NC), or when the

trip temperature is set to a value at least 4NC above the

current temperature.

Table 7. ALERT High Status Register (44h)

BIT NAME POR

STATE FUNCTION

7 (MSB) Remote ALERT

High 7 0

Channel 7 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 7

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 7 ALERT High Limit register.

6Local ALERT

High 0Local Channel High-Alert Bit. This bit is set to logic 1 when the local temperature

exceeds the temperature threshold limit in the Local ALERT High Limit register.

5Remote ALERT

High 6 0

Channel 6 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 6

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 6 ALERT High Limit register.

4Remote ALERT

High 5 0

Channel 5 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 5

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 5 ALERT High Limit register.

3Remote ALERT

High 4 0

Channel 4 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 4

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 4 ALERT High Limit register.

2Remote ALERT

High 3 0

Channel 3 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 3

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 3 ALERT High Limit register.

1Remote ALERT

High 2 0

Channel 2 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 2

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 2 ALERT High Limit register.

0Remote ALERT

High 1 0

Channel 1 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 1

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 1 ALERT High Limit register.

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

______________________________________________________________________________________ 17

Table 8. OVERT Status Register (45h)

Table 9. Diode Fault Status Register (46h)

BIT NAME POR

STATE FUNCTION

7 (MSB) Remote OVERT 7 0

Channel 7 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 7 remote-diode temperature exceeds the temperature threshold limit in

the Remote 7 OVERT High Limit register.

6Local OVERT 0

Local Channel Overtemperature Status Bit. This bit is set to logic 1 when the local

temperature exceeds the temperature threshold limit in the Local OVERT High Limit

5Remote OVERT 6 0

Channel 6 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 6 remote-diode temperature exceeds the temperature threshold limit in

the Remote 6 OVERT High Limit register.

4Remote OVERT 5 0

Channel 5 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 5 remote-diode temperature exceeds the temperature threshold limit in

the Remote 5 OVERT High Limit register.

3Remote OVERT 4 0

Channel 4 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 4 remote-diode temperature exceeds the temperature threshold limit in

the Remote 4 OVERT High Limit register.

2Remote OVERT 3 0

Channel 3 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 3 remote-diode temperature exceeds the temperature threshold limit in

the Remote 3 OVERT High Limit register.

1Remote OVERT 2 0

Channel 2 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 2 remote-diode temperature exceeds the temperature threshold limit in

the Remote 2 OVERT High Limit register.

0Remote OVERT 1 0

Channel 1 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 1 remote-diode temperature exceeds the temperature threshold limit in

the Remote 1 OVERT High Limit register.

BIT NAME POR

STATE FUNCTION

7 (MSB) RESERVED 0 —

6 Diode Fault 7 0 Channel 7 Remote-Diode Fault Bit. This bit is set to 1 when DXP7 and DXN7 are open

circuit or when DXP7 is connected to VCC.

5 Diode Fault 6 0 Channel 6 Remote-Diode Fault Bit. This bit is set to 1 when DXP6 and DXN6 are open

circuit or when DXP6 is connected to VCC.

4 Diode Fault 5 0 Channel 5 Remote-Diode Fault Bit. This bit is set to 1 when DXP5 and DXN5 are open

circuit or when DXP5 is connected to VCC.

3 Diode Fault 4 0 Channel 4 Remote-Diode Fault Bit. This bit is set to 1 when DXP4 and DXN4 are open

circuit or when DXP4 is connected to VCC.

2 Diode Fault 3 0 Channel 3 Remote-Diode Fault Bit. This bit is set to 1 when DXP3 and DXN3 are open

circuit or when DXP3 is connected to VCC.

1 Diode Fault 2 0 Channel 2 Remote-Diode Fault Bit. This bit is set to 1 when DXP2 and DXN2 are open

circuit or when DXP2 is connected to VCC.

0 Diode Fault 1 0 Channel 1 Remote-Diode Fault Bit. This bit is set to 1 when DXP1 and DXN1 are open

circuit or when DXP1 is connected to VCC.

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

18 _____________________________________________________________________________________

Effect of Ideality Factor

The accuracy of the remote temperature measurements

depends on the ideality factor (n) of the remote “diode”

(actually a transistor). The default value for the MAX6581

is n = 1.008 (channels 1–7). A thermal diode on the

substrate of an IC is normally a pnp with the base and

emitter brought out and the collector (diode connection)

grounded. DXP_ must be connected to the anode (emit-

ter) and DXN_ must be connected to the cathode (base)

of this pnp. If a sense transistor with an ideality factor

other than 1.008 is used, the output data is different from

the data obtained with the optimum ideality factor. If

necessary, a different ideality factor value can be chosen

using the Transistor Ideality register (see Table 11). The

Ideality Select register allows each channel to have the

default ideality of 1.008 or the value programmed in the

Transistor Ideality register.

Table 10. ALERT Low Status Register (47h)

BIT NAME POR

STATE FUNCTION

7 (MSB) Remote ALERT

Low 7 0

Channel 7 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 7

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 7 ALERT Low Limit register.

6Local ALERT Low 0

Local Channel Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the local

channel remote-diode temperature falls below the programmed temperature threshold

limit in the Local ALERT Low Limit register.

5Remote ALERT

Low 6 0

Channel 6 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 6

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 6 ALERT Low Limit register.

4Remote ALERT

Low 5 0

Channel 5 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 5

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 5 ALERT Low Limit register.

3Remote ALERT

Low 4 0

Channel 4 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 4

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 4 ALERT Low Limit register.

2Remote ALERT

Low 3 0

Channel 3 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 3

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 3 ALERT Low Limit register.

1Remote ALERT

Low 2 0

Channel 2 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 2

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 2 ALERT Low Limit register.

0Remote ALERT

Low 1 0

Channel 1 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 1

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 1 ALERT Low Limit register.

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

______________________________________________________________________________________ 19

Table 11. Transistor Ideality Register

X = Don’t care.

FACTOR HEX

0x4B

X X X 0 0 0 0 0 .999 0x00

X X X 0 0 0 0 1 1.000 0x01

X X X 0 0 0 1 0 1.001 0x02

X X X 0 0 0 1 1 1.002 0x03

X X X 0 0 1 0 0 1.003 0x04

X X X 0 0 1 0 1 1.004 0x05

X X X 0 0 1 1 0 1.005 0x06

X X X 0 0 1 1 1 1.006 0x07

X X X 0 1 0 0 0 1.007 0x08

X X X 0 1 0 0 1 1.008 0x09

X X X 0 1 0 1 0 1.009 0x0A

X X X 0 1 0 1 1 1.010 0x0B

X X X 0 1 1 0 0 1.011 0x0C

X X X 0 1 1 0 1 1.012 0x0D

X X X 0 1 1 1 0 1.013 0x0E

X X X 0 1 1 1 1 1.014 0x0F

X X X 1 0 0 0 0 1.015 0x10

X X X 1 0 0 0 1 1.016 0x11

X X X 1 0 0 1 0 1.017 0x12

X X X 1 0 0 1 1 1.018 0x13

X X X 1 0 1 0 0 1.019 0x14

X X X 1 0 1 0 1 1.020 0x15

X X X 1 0 1 1 0 1.021 0x16

X X X 1 0 1 1 1 1.022 0x17

X X X 1 1 0 0 0 1.023 0x18

X X X 1 1 0 0 1 1.024 0x19

X X X 1 1 0 1 0 1.025 0x1A

X X X 1 1 0 1 1 1.026 0x1B

X X X 1 1 1 0 0 1.027 0x1C

X X X 1 1 1 0 1 1.028 0x1D

X X X 1 1 1 1 0 1.029 0x1E

X X X 1 1 1 1 1 1.030 0x1F

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

20 _____________________________________________________________________________________

Series-Resistance Cancellation

Some thermal diodes on high-power ICs have exces-

sive series resistance that can cause temperature-mea-

surement errors when used with conventional remote-

temperature sensors. Channels 1–7 of the MAX6581

have a series-resistance cancellation feature (enabled

by bits [7:0] of the Resistance Cancellation register) that

eliminates the effect of diode series resistance and inter-

connection resistance. Set these bits to 1 if the series

resistance is large enough to affect the accuracy of the

channels. The series-resistance cancellation function

increases the conversion time for the remote channels by

125ms (typ). This feature cancels the bulk resistance of

the sensor and any other resistance in series (e.g., wire,

contact resistance, etc.). The cancellation range is from

0I to 100I.

Applications Information

Remote-Diode Selection

The MAX6581 directly measures the die temperature of CPUs

and other ICs that have on-chip temperature-sensing diodes

(see the Typical Application Circuit), or it can measure the

temperature of a discrete diode-connected transistor.

Discrete Remote Diodes

When the remote-sensing diode is a discrete transistor,

its collector and base must be connected together. Table

13 lists examples of discrete transistors that are appro-

priate for use with the MAX6581. The transistor must be

a small-signal type with a relatively high forward voltage;

otherwise, the A/D input-voltage range can be violated.

The forward voltage at the highest expected temperature

must be greater than 0.25V at 10FA, and at the lowest

expected temperature the forward voltage must be less

than 0.95V at 100FA. Large power transistors must not

be used. Also, ensure that the base resistance is less

than 100I. Tight specifications for forward-current gain

(e.g., 50 < A < 150) indicate that the manufacturer has

good process controls and that the devices have con-

sistent VBE characteristics. Manufacturers of discrete

transistors do not normally specify or guarantee ideality

factor. This normally is not a problem since good-quality

discrete transistors tend to have ideality factors that fall

within a relatively narrow range. Variations in remote

temperature readings of less than Q2NC with a variety of

discrete transistors have been observed. However, it is

good design practice to verify good consistency of tem-

perature readings with several discrete transistors from

any supplier under consideration.

Table 12. Resistance Cancellation Register (4Ah)

X = Don’t care.

BIT NAME POR

STATE FUNCTION

7 (MSB) X 0 —

6RESISTANCE

CANCELLATION 7 0Channel 7 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

5RESISTANCE

CANCELLATION 6 0Channel 6 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

4RESISTANCE

CANCELLATION 5 0Channel 5 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

3RESISTANCE

CANCELLATION 4 0Channel 4 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

2RESISTANCE

CANCELLATION 3 0Channel 3 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

1RESISTANCE

CANCELLATION 2 0Channel 2 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

0RESISTANCE

CANCELLATION 1 0Channel 1 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

______________________________________________________________________________________ 21

Unused Diode Channels

If one or more of the remote-diode channels is not

needed, disconnect the DXP_ and DXN_ inputs for

that channel, or connect the DXP_ to the correspond-

ing DXN_. The status register indicates a diode “fault”

for this channel and the channel is ignored during the

temperature-measurement sequence. It is also good

practice to mask any unused channels immediately upon

power-up by setting the appropriate bits in the ALERT

Mask and OVERT Mask registers. This prevents unused

channels from causing ALERT or OVERT to assert.

Thermal Mass and Self-Heating

When sensing local temperature, the MAX6581 mea-

sures the temperature of the PCB to which it is soldered.

The leads provide a good thermal path between the PCB

traces and the die. As with all IC temperature sensors,

thermal conductivity between the die and the ambient

air is poor by comparison, making air-temperature mea-

surements impractical. Since the thermal mass of the

PCB is far greater than that of the MAX6581, the device

follows temperature changes on the PCB with little or no

perceivable delay. When measuring the temperature of a

CPU, or other IC with an on-chip sense junction, thermal

mass has virtually no effect; the measured temperature

of the junction tracks the actual temperature within a

conversion cycle. When measuring temperature with

discrete remote transistors, the best thermal-response

times are obtained with transistors in small packages

(i.e., SOT23 or SC70). Take care to account for thermal

gradients between the heat source and the sensor,

and ensure that stray air currents across the sensor

package do not interfere with measurement accuracy.

Self-heating does not significantly affect measurement

accuracy. Remote-sensor self-heating due to the diode

current source is negligible.

ADC Noise Filtering

The integrating ADC has good noise rejection for low-

frequency signals, such as power-supply hum. In envi-

ronments with significant high-frequency EMI, connect

an external 100pF capacitor between DXP_ and DXN_.

Larger capacitor values can be used for added filter-

ing; however, it can introduce errors due to the rise time

of the switched current source. High-frequency noise

reduction is needed for high-accuracy remote measure-

ments. Noise can be reduced with careful PCB layout as

discussed in the PCB Layout section.

Slave Address

The slave address for the MAX6581 is shown in Table 14.

Table 13. Remote Sensors Transistor Suppliers (for Channels 1–7)

Note: Discrete transistors must be diode connected (base shorted to collector).

Table 14. Slave Address

DEVICE ADDRESS

A7 A6 A5 A4 A3 A2 A1 A0

1001101R/W

SUPPLIER MODEL NO.

PNP NPN

Central Semiconductor Corp. (USA) CMPT3906

2N3906

CMPT3904

2N3904

Fairchild Semiconductor (USA) MMBT3906

2N3906 2N3904

Infineon (Germany) SMBT3906 —

ON Semiconductor (USA) MMBT3906

2N3906 2N3904

ROHM Semiconductor (USA) SST3906 SST3904

Samsung (Korea) KST3906-TF KST3904-TF

Siemens (Germany) SMBT3906 SMBT3904

Zetex (England) FMMT3906CT-ND FMMT3904CT-ND

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

22 _____________________________________________________________________________________

PCB Layout

Follow the guidelines below to reduce the measurement

error when measuring remote temperature:

1) Place the MAX6581 as close as possible to the

remote diode. In noisy environments, such as a com-

puter motherboard, this distance is typically 4in to

8in. This length can be increased if the worst-noise

sources are avoided. Noise sources include displays,

clock generators, memory buses, and PCI buses.

2) Do not route the DXP_–DXN_ lines next to the deflec-

tion coils of a CRT. Also, do not route the traces

across fast digital signals, which can easily introduce

+30NC error, even with good filtering.

3) Route the DXP_ and DXN_ traces in parallel and in

close proximity to each other. Each parallel pair of

traces should go to a remote diode. Route these

traces away from any higher voltage traces, such as

+12VDC. Leakage currents from PCB contamination

must be dealt with carefully since a 20MI leakage

path from DXP_ to ground causes approximately

+1NC error. If high-voltage traces are unavoidable,

connect guard traces to GND on either side of the

DXP_–DXN_ traces (Figure 5).

4) Route through as few vias and crossunders as possi-

ble to minimize copper/solder thermocouple effects.

5) Use wide traces when possible (5-mil to 10-mil traces

are typical). Be aware of the effect of trace resistance

on temperature readings when using long, narrow

traces.

6) When the power supply is noisy, add a resistor (up to

47I) in series with VCC.

Twisted-Pair and Shielded Cables

Use a twisted-pair cable to connect the remote sensor

for remote-sensor distances longer than 8in or in very

noisy environments. Twisted-pair cable lengths can be

between 6ft and 12ft before noise introduces excessive

errors. For longer distances, the best solution is a shield-

ed twisted pair such as those used for audio micro-

phones. For example, Belden #8451 works well for dis-

tances up to 100ft in a noisy environment. At the device,

connect the twisted-pair cables to DXP_ and DXN_ and

the shielded cable to GND. Leave the shielded cable

unconnected at the remote sensor. For very long cable

runs, the cable’s parasitic capacitance often provides

noise filtering; therefore the 100pF capacitor can often

be removed or reduced in value. Cable resistance also

affects remote-sensor accuracy. For every 1I of series

resistance, the error is approximately +0.5NC.

Figure 5. Recommended DXP_–DXN_ PCB Traces. The two

outer guard traces are recommended if high-voltage traces

are near the DXN_ and DXP_ traces.

5–10 mils

MINIMUM

5–10 mils

GND

DXP_

DXN_

GND

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

______________________________________________________________________________________ 23

Typical Application Circuit

Chip Information

PROCESS: BiCMOS

Package Information

For the latest package outline information and land patterns,

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.

DXP2 ALERT

VCC

OVERT

STBY

DXP7

I.C.

24 23 22 21 20 19

DXN2

DXP1 N.C. GND

+3.3V

SMBCLK SMBDATA

CPU

FPGA

ASIC

100pF

DXP3

DXN3

DXN1

DXN7

100pF

100pF100pF

10 11

DXN6 DXP6

87 9

DXP5DXN4 DXN5

4.7kI4.7kI4.7kI4.7kI

TO µP

0.1µF

DXP4

N.C.

MAX6581

PACKAGE

TYPE

PACKAGE

CODE

OUTLINE

NO.

LAND

PATTERN NO.

24 TQFN-EP T2444+4 21-0139 90-0022

±1°C Accurate 8-Channel Temperature Sensor

MAX6581

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.

24 Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

Revision History

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

0 8/10 Initial release —