General Description
The MAX6642 is a precise, two-channel digital temper-
ature sensor. It accurately measures the temperature of
its own die and a remote PN junction, and reports the
temperature data over a 2-wire serial interface. The
remote PN junction is typically a substrate PNP transis-
tor on the die of a CPU, ASIC, GPU, or FPGA. The
remote PN junction can also be a discrete diode-con-
nected small-signal transistor.
The 2-wire serial interface accepts standard system
management bus (SMBus™), Write Byte, Read Byte,
Send Byte, and Receive Byte commands to read the
temperature data and to program the alarm thresholds.
To enhance system reliability, the MAX6642 includes an
SMBus timeout. The temperature data format is 10 bit
with the least significant bit (LSB) corresponding to
+0.25°C. The ALERT output asserts when the local or
remote overtemperature thresholds are violated. A fault
queue may be used to prevent the ALERT output from
setting until two consecutive faults have been detected.
Measurements can be done autonomously or in a sin-
gle-shot mode.
Remote accuracy is ±1°C maximum error between
+60°C and +100°C. The MAX6642 operates from -40°C
to +125°C, and measures remote temperatures
between 0°C and +150°C. The MAX6642 is available in
a 6-pin TDFN package.
Applications
Desktop Computers
Notebook Computers
Servers
Thin Clients
Test and Measurement
Workstations
Graphic Cards
Features
♦Dual Channel: Measures Remote and Local
Temperature
♦+0.25°C Resolution
♦High Accuracy ±1°C (max) (Remote) and
±2°C (Local) from +60°C to +100°C
♦Measures Remote Temperature Up to +150°C
♦Programmable Overtemperature Alarm
Temperature Thresholds
♦SMBus/I2CTM-Compatible Interface
♦Tiny TDFN Package
MAX6642
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-2920; Rev 0; 8/03
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
PART TEMP RANGE PIN-PACKAGE
MAX6642ATT90-T -40°C to +125°C 6 TDFN
MAX6642ATT92-T -40°C to +125°C 6 TDFN
MAX6642ATT94-T -40°C to +125°C 6 TDFN
MAX6642ATT96-T -40°C to +125°C 6 TDFN
MAX6642ATT98-T -40°C to +125°C 6 TDFN
MAX6642ATT9A-T -40°C to +125°C 6 TDFN
MAX6642ATT9C-T -40°C to +125°C 6 TDFN
MAX6642ATT9E-T -40°C to +125°C 6 TDFN
MAX6642
2200pF
0.1µF
µP
DXP
GND
SDA
SCLK
ALERT
DATA
CLOCK
INTERRUPT TO µP
47Ω
10kΩ EACH
3.3V
VCC
Typical Operating Circuit
PART
MEASURED TEMP RANGE
TOP
MARK
MAX6642ATT90-T 0°C to +150°C
AFC
MAX6642ATT92-T 0°C to +150°C
AFD
MAX6642ATT94-T 0°C to +150°C
AFE
MAX6642ATT96-T 0°C to +150°C
AFF
MAX6642ATT98-T 0°C to +150°C
AEW
MAX6642ATT9A-T 0°C to +150°C
AFG
MAX6642ATT9C-T 0°C to +150°C
AFH
MAX6642ATT9E-T 0°C to +150°C AFI
Selector Guide
SMBus is a trademark of Intel Corp.
Purchase of I2C components of Maxim Integrated Products, Inc.
or one of its sublicensed Associated Companies, conveys a
license under the Philips I2C Patent Rights to use these compo-
nents in an I2C system, provided that the system conforms to the
I2C Standard Specification as defined by Philips.
Pin Configuration and Functional Diagram appear at end of
data sheet.
MAX6642
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = +3.0V to +5.5V, TA = -40°C to +125°C, unless otherwise specified. Typical values are at VCC = +3.3V and TA = +25°C.) (Note 1)
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 ...........................................................................-0.3V to +6V
DXP.............................................................-0.3V to (VCC + 0.3V)
SCLK, SDA, ALERT ..................................................-0.3V to +6V
SDA, ALERT Current ...........................................-1mA to +50mA
Continuous Power Dissipation (TA= +70°C)
6-Pin TDFN (derate 24.4mW/°C above +70°C) .........1951mW
ESD Protection (all pins, Human Body Model) ................±2000V
Junction Temperature......................................................+150°C
Operating Temperature Range .........................-40°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage VCC 3.0 5.5 V
0.25 °C
Temperature Resolution 10 Bits
TRJ = +60°C to +100°C,
TA = +25°C to +85°C-1.0 +1.0
TRJ = 0°C to +125°C -3.0 +3.0
Remote Temperature Error VCC = 3.3V
TRJ = +125°C to +150°C -3.5 +3.5
°C
TA = +60°C to +100°C -2.0 +2.0
Local Temperature Error VCC = 3.3V TA = 0°C to +125°C -3.0 +3.0 °C
Supply Sensitivity of Temperature
Error ±0.2 °C/V
Undervoltage Lockout Threshold UVLO Falling edge of VCC disables ADC 2.4 2.7 2.95 V
Undervoltage Lockout Hysteresis 90 mV
Power-On-Reset (POR) Threshold VCC falling edge 1.5 2.0 2.4 V
POR Threshold Hysteresis 90 mV
Standby Supply Current SMBus static 3 10 µA
Operating Current During conversion 0.5 1.0 mA
Average Operating Current 260 µA
Conversion Time tCONV From stop bit to conversion completion 106 125 143 ms
Conversion Rate fCONV 8Hz
High level 80 100 120
Remote-Diode Source Current IRJ Low level 8 10 12 µA
ALERT
VOL = 0.4V 1
Output-Low Sink Current VOL = 0.6V 4 mA
Output-High Leakage Current VOH = VCC 1µA
MAX6642
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
_______________________________________________________________________________________ 3
Note 1: All parameters tested at TA= +25°C. Specifications over temperature are guaranteed by design.
Note 2: Timing specifications guaranteed by design.
Note 3: The serial interface resets when SCLK is low for more than tTIMEOUT.
Note 4: A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCLK’s falling edge.
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +5.5V, TA = -40°C to +125°C, unless otherwise specified. Typical values are at VCC = +3.3V and TA = +25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SMBus-COMPATIBLE INTERFACE (SCLK and SDA)
Logic Input Low Voltage VIL 0.8 V
Logic Input High Voltage VIH VCC = 3.0V 2.2 V
Input Leakage Current ILEAK VIN = GND or 5.5V -1 +1 µA
Output Low Sink Current IOL VOL = 0.6V 6 mA
Input Capacitance CIN 5pF
SMBus TIMING (Note 2)
Serial Clock Frequency fSCLK (Note 3) 100 kHz
Bus Free Time Between STOP
and START Condition tBUF 4.7 µs
START Condition Setup Time 4.7 µs
Repeat START Condition Setup
Time tSU:STA 90% to 90% 50 ns
START Condition Hold Time tHD:STA 10% of SDA to 90% of SCLK 4 µs
STOP Condition Setup Time tSU:STO 90% of SCLK to 90% of SDA 4 µs
Clock Low Period tLOW 10% to 10% 4.7 µs
Clock High Period tHIGH 90% to 90% 4 µs
Data Setup Time tHD:DAT (Note 4) 250 µs
Receive SCLK/SDA Rise Time tR1µs
Receive SCLK/SDA Fall Time tF300 ns
Pulse Width of Spike Suppressed tSP 050ns
SMBus Timeout tTIMEOUT SDA low period for interface reset 20 28 40 ms
MAX6642
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
4 _______________________________________________________________________________________
Typical Operating Characteristics
(VCC = 3.3V, TA= +25°C, unless otherwise noted.)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0.01 0.1 1 10 100
STANDBY SUPPLY CURRENT
vs. CLOCK FREQUENCY
MAX6642 toc01
CLOCK FREQUENCY (kHz)
SUPPLY CURRENT (µA)
-4
-2
-3
0
-1
1
2
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
MAX6642 toc02
TEMPERATURE (°C)
TEMPERATURE ERROR (°C)
0507525 100 125
2N3906
-3
-1
-2
1
0
2
3
0125
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
MAX 6642 toc03
TEMPERATURE (°C)
TEMPERATURE ERROR (°C)
5025 75 100
-1.5
-0.5
-1.0
0.5
0
1.5
1.0
2.0
0.0001 0.01 0.10.001 1 10 100
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6642 toc04
FREQUENCY (kHz)
TEMPERATURE ERROR (°C)
VIN = 100mVP-P SQUARE WAVE
APPLIED TO VCC WITH NO BYPASS CAPACITOR
LOCAL ERROR
REMOTE ERROR
0
30
20
10
40
50
60
70
80
90
100
0.001 0.10.01 1 10 100
TEMPERATURE ERROR
vs. DXP NOISE FREQUENCY
MAX6642 toc05
FREQUENCY (kHz)
TEMPERATURE ERROR (°C)
LOCAL ERROR
REMOTE ERROR
VIN = AC-COUPLED TO DXP
VIN = 100mVP-P SQUARE WAVE
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0
1.0
2.0
0.1 1 10 100
TEMPERATURE ERROR
vs. DXP-GND CAPACITANCE
MAX6642 toc06
DXP-GND CAPACITANCE (nF)
TEMPERATURE ERROR (°C)
Detailed Description
The MAX6642 is a temperature sensor for local
and remote temperature-monitoring applications.
Communication with the MAX6642 occurs through the
SMBus-compatible serial interface and dedicated alert
pins. ALERT asserts if the measured local or remote
temperature is greater than the software-programmed
ALERT limit.
The MAX6642 converts temperatures to digital data
either at a programmed rate of eight conversions per
second or in single conversions. Temperature data is
represented by 8 data bits (at addresses 00h and 01h),
with the LSB equal to +1°C and the MSB equal to
+128°C. Two additional bits of remote temperature data
are available in the “extended” register at address 10h
and 11h (Table 2) providing resolution of +0.25°C.
ADC and Multiplexer
The averaging ADC integrates over a 60ms period
(each channel, typ), with excellent noise rejection.
The multiplexer automatically steers bias currents
through the remote and local diodes. The ADC and
associated circuitry measure each diode’s forward volt-
age and compute the temperature based on this volt-
age. Both channels are automatically converted once
the conversion process has started, either in free-run-
ning or single-shot mode. If one of the two channels is
not used, the device still performs both measurements,
and the user can ignore the results of the unused chan-
nel. If the remote-diode channel is unused, connect
DXP to GND rather than leaving DXP open.
The conversion time per channel (remote and internal)
is 125ms. If both channels are being used, then each
channel is converted four times per second. If the
external conversion-only option is selected, then the
remote temperature is measured eight times per sec-
ond. The results of the previous conversion are always
available, even if the ADC is busy.
Low-Power Standby Mode
Standby mode reduces the supply current to less than
10µA by disabling the ADC and timing circuitry. Enter
standby mode by setting the RUN bit to 1 in the config-
uration byte register (Table 4). All data is retained in
memory, and the SMBus interface is active and listen-
ing for SMBus commands. Standby mode is not a shut-
down mode. With activity on the SMBus, the device
draws more supply current (see the Typical Operating
Characteristics). In standby mode, the MAX6642 can
be forced to perform ADC conversions through the
one-shot command, regardless of the RUN bit status.
If a standby command is received while a conversion is
in progress, the conversion cycle is truncated, and the
data from that conversion is not latched into a tempera-
ture register. The previous data is not changed and
remains available.
Supply-current drain during the 125ms conversion peri-
od is 500µA (typ). In standby mode, supply current
drops to 3µA (typ).
SMBus Digital Interface
From a software perspective, the MAX6642 appears as
a set of byte-wide registers that contain temperature
data, alarm threshold values, and control bits. A stan-
dard SMBus-compatible 2-wire serial interface is used
to read temperature data and write control bits and
alarm threshold data.
The MAX6642 employs four standard SMBus protocols:
Write Byte, Read Byte, Send Byte, and Receive Byte.
(Figures 1, 2, and 3). The shorter Receive Byte protocol
allows quicker transfers, provided that the correct data
MAX6642
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
_______________________________________________________________________________________ 5
Pin Description
PIN NAME FUNCTION
1V
CC Supply Voltage Input, +3V to +5.5V. Bypass VCC to GND with a 0.1µF capacitor. A 47Ω series resistor is
recommended but not required for additional noise filtering.
2 GND Ground
3 DXP Combined Remote-Diode Current Source and ADC Input for Remote-Diode Channel. Place a 2200pF
capacitor between DXP and GND for noise filtering.
4 SCLK SMBus Serial-Clock Input. May be pulled up to +5.5V regardless of VCC.
5 SDA SMBus Serial-Data Input/Output, Open Drain. May be pulled up to +5.5V regardless of VCC.
6ALERT SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds user-set limits. See
the
ALERT
Interrupts section.
MAX6642
register was previously selected by a Write Byte
instruction. Use caution when using the shorter proto-
cols in multimaster systems, as a second master could
overwrite the command byte without informing the first
master.
Read temperature data from the read internal tempera-
ture (00h) and read external temperature (01h) regis-
ters. The temperature data format for these registers is
8 bits for each channel, with the LSB representing +1°C
(Table 1).
Read the additional bits from the read extended tem-
perature byte register (10h, 11h), which extends the
data to 10 bits and the resolution to +0.25°C per LSB
(Table 2).
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
6 _______________________________________________________________________________________
S ADDRESS WR ACK ACK PDATA ACKCOMMAND
7 BITS 18 BITS8 BITS
SLAVE ADDRESS: EQUIVA-
LENT 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
SADDRESSADDRESS WR ACK ACK PS RD ACK ///DATACOMMAND
7 BITS 7 BITS 8 BITS8 BITS
READ BYTE FORMAT
SLAVE ADDRESS: EQUIVA-
LENT TO CHIP SELECT LINE
COMMAND BYTE: SELECTS
WHICH REGISTER YOU ARE
REDING FROM
SPADDRESS WR ACK ACKCOMMAND
7 BITS 8 BITS
SEND BYTE FORMAT
COMMAND BYTE: SENDS COM-
MAND WITH NO DATA, USUALLY
USED FOR ONE-SHOT COMMAND
SPADDRESS 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
Figure 1. SMBus Protocols
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
AB CD
EFG HIJ
SMBDATA
tSU:STA tHD:STA
tLOW tHIGH
tSU:DAT tSU:STO tBUF
LMK
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 = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
Figure 2. SMBus Write Timing Diagram
When a conversion is complete, the main temperature
register and the extended temperature register are
updated.
Alarm Threshold Registers
Two registers store ALERT threshold values—one each
for the local and remote channels. If either measured
temperature equals or exceeds the corresponding
ALERT threshold value, the ALERT interrupt asserts
unless the ALERT bit is masked.
The power-on-reset (POR) state of the local ALERT
THIGH register is +70°C (0100 0110). The POR state of
the remote ALERT THIGH register is +120°C (0111 1000).
Diode Fault Detection
A continuity fault detector at DXP detects an open cir-
cuit on DXP, or a DXP short to VCC or GND. If an open
or short circuit exists, the external temperature register
is loaded with 1111 1111 and status bit 2 (OPEN) of the
status byte is set to 1. Immediately after POR, the sta-
tus register indicates that no fault is present. If a fault is
present upon power-up, the fault is not indicated until
the end of the first conversion. Diode faults do not set
the ALERT output.
ALERT
Interrupts
The ALERT interrupt occurs when the internal or external
temperature reading exceeds a high temperature limit
(user programmed). The ALERT interrupt output signal is
latched and can be cleared only by reading the status
register after the fault condition no longer exists or by
successfully responding to the alert response address. If
the ALERT is cleared by responding to the alert
response address and the temperature fault condition
still exists, ALERT is reasserted after the next tempera-
ture-monitoring cycle. To clear ALERT while the tempera-
ture is above the trip threshold, write a new high limit that
is higher than the current temperature. The ALERT out-
put is open drain, allowing multiple devices to share a
common interrupt line.
Alert Response Address
The SMBus alert response interrupt pointer provides
quick fault identification for simple slave devices like
temperature sensors. Upon receiving an ALERT inter-
rupt signal, the host master can broadcast a Receive
Byte transmission to the alert response slave address
MAX6642
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
_______________________________________________________________________________________ 7
SMBCLK
AB CD
EFG H
IJK
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
LM
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
Figure 3. SMBus Read Timing Diagram
TEMP (°C) DIGITAL OUTPUT
130.00 1 000 0010
127.00 0 111 1111
126.00 0 111 1110
25 0 001 1001
0.00 0 000 0000
<0.00 0 000 0000
Diode fault (short or open) 1 111 1111
Table 1. Main Temperature Register
(High Byte) Data Format
FRACTIONAL TEMP (°C) DIGITAL OUTPUT
0.000 00XX XXXX
0.250 01XX XXXX
0.500 10XX XXXX
0.750 11XX XXXX
Table 2. Extended Resolution
Temperature Register (Low Byte) Data
Format
MAX6642
(0001 100). Following such a broadcast, 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
acknowledge 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 interrupt latch. If the condition still exists, the
device reasserts the ALERT interrupt at the end of the
next conversion.
Command Byte Functions
The 8-bit command byte register (Table 3) is the master
index that points to the various other registers within the
MAX6642. The register’s POR state is 0000 0000, so a
Receive Byte transmission (a protocol that lacks the
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
8 _______________________________________________________________________________________
A D D R ESS PO R ST A T EF U N C T IO N
00h 00h ( 0000 0000) Read l ocal tem p er atur e
01h 00h ( 0000 0000) Read r em ote tem p er atur e
02h N /A Read status b yte
03h 10h ( 0001 0000) Read confi g ur ati on b yte
05h 46h ( 0100 0110) + 70° C Read l ocal hi g h l i m i t
07h 78h ( 0111 1000) + 120° C Read r em ote hi g h l i m i t
09h N /A W r i te confi g ur ati on b yte
0Bh N /A W r i te l ocal hi g h l i m i t
0D hN /A W r i te r em ote hi g h l i m i t
0Fh N /A S i ng l e shot
10h 0000 0000 Read r em ote extend ed
tem p er atur e
11h 0000 0000 Read i nter nal extend ed
tem p er atur e
FE h4D h ( 0100 1101) Read m anufactur er ID
Table 3. Command-Byte Assignments
BIT NAME POR STATE FUNCTION
7 (MSB) MASK1 0 A 1 masks off (disables) the ALERT interrupts.
6 STOP/RUN 0 A 1 puts the MAX6642 into standby mode.
5 External only 0
A 1 disables local temperature measurements so that only
remote temperature is measured. The measurement rate
becomes 8Hz.
4Fault
queue 10: ALERT is set by a single fault. 1: Two consecutive faults
are required to set ALERT.
3 to 0 —0000 Reserved.
Table 4. Configuration-Byte Bit Assignments
BIT NAME POR STATE FUNCTION
7 (MSB) BUSY 0 A 1 indicates the MAX6642 is busy converting.
6 LHIGH 0 A 1 indicates an internal high-temperature fault. Clear
LHIGH with a POR or by reading the status byte.
5—0 Reserved.
4 RHIGH 0 A 1 indicates an external high-temperature fault. Clear
RHIGH with a POR or by reading the status byte.
3—0 Reserved.
2 OPEN 0
A 1 indicates a diode open condition. Clear OPEN with a
POR or by reading the status byte when the condition no
longer exists.
1 to 0 —0 Reserved.
Table 5. Status-Byte Bit Assignments
command byte) that occurs immediately after POR
returns the current local temperature data.
Single-Shot
The single-shot command immediately forces a new
conversion cycle to begin. If the single-shot command
is received while the MAX6642 is in standby mode
(RUN bit = 1), a new conversion begins, after which the
device returns to standby mode. If a single-shot con-
version is in progress when a single-shot command is
received, the command is ignored. If a single-shot
command is received in autonomous mode (RUN bit =
0), the command is ignored.
Configuration Byte Functions
The configuration byte register (Table 4) is a read-write
register with several functions. Bit 7 is used to mask
(disable) interrupts. Bit 6 puts the MAX6642 into stand-
by mode (STOP) or autonomous (RUN) mode. Bit 5 dis-
ables local temperature conversions for faster (8Hz)
remote temperature monitoring. Bit 4 prevents setting
the ALERT output until two consecutive measurements
result in fault conditions.
Status Byte Functions
The status byte register (Table 5) indicates which (if
any) temperature thresholds have been exceeded. This
byte also indicates whether the ADC is converting and
whether there is an open-circuit fault detected on the
external sense junction. After POR, the normal state of
all flag bits is zero, assuming no alarm conditions are
present. The status byte is cleared by any successful
read of the status byte after the overtemperature fault
condition no longer exists.
Slave Addresses
The MAX6642 has eight fixed addresses available.
These are shown in Table 6.
The MAX6642 also responds to the SMBus alert
response slave address (see the Alert Response
Address section).
POR and UVLO
To prevent ambiguous power-supply conditions from
corrupting the data in memory and causing erratic
behavior, a POR voltage detector monitors VCC and
clears the memory if VCC falls below 2.1 (typ). When
power is first applied and VCC rises above 2.1 (typ),
the logic blocks begin operating, although reads and
writes at VCC levels below 3V are not recommended. A
second VCC comparator, the ADC undervoltage lockout
(UVLO) comparator prevents the ADC from converting
until there is sufficient headroom (VCC = +2.7V typ).
Power-Up Defaults
Power-up defaults include:
•ALERT output is cleared.
•ADC begins autoconverting at a 4Hz rate.
•Command byte is set to 00h to facilitate quick
local Receive Byte queries.
•Local (internal) THIGH limit set to +70°C.
•Remote (external) THIGH limit set to +120°C.
Applications Information
Remote-Diode Selection
The MAX6642 can directly measure the die temperature
of CPUs and other ICs that have on-board temperature-
sensing diodes (see the Typical Operating Circuit) or
they can measure the temperature of a discrete diode-
connected transistor.
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 MAX6642 is optimized for n
= 1.008, which is the typical value for the Intel Pentium
III. A thermal diode on the substrate of an IC is normally
a PNP with its collector grounded. DXP should be con-
nected to the anode (emitter) and the cathode should
be connected at GND of the MAX6642.
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. Fortunately,
the difference is predictable.
Assume a remote-diode sensor designed for a nominal
ideality factor nNOMINAL is used to measure the tem-
perature of a diode with a different ideality factor n1.
The measured temperature TMcan be corrected using:
TT n
n
M ACTUAL
NOMINAL
=
1
MAX6642
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
_______________________________________________________________________________________ 9
PART NO. SUFFIX ADDRESS
MAX6642ATT90 1001 000
MAX6642ATT92 1001 001
MAX6642ATT94 1001 010
MAX6642ATT96 1001 011
MAX6642ATT98 1001 100
MAX6642ATT9A 1001 101
MAX6642ATT9C 1001 110
MAX6642ATT9E 1001 111
Table 6. Slave Address
MAX6642
where temperature is measured in Kelvin and
nNOMIMAL for the MAX6642 is 1.008.
As an example, assume you want to use the MAX6642
with a CPU that has an ideality factor of 1.002. If the
diode has no series resistance, the measured data is
related to the real temperature as follows:
For a real temperature of +85°C (358.15K), the mea-
sured temperature is +82.91°C (356.02K), an error of
-2.13°C.
Effect of Series Resistance
Series resistance in a sense diode contributes addition-
al errors. For nominal diode currents of 10µA and
100µA, the change in the measured voltage due to
series resistance is:
∆VM= RS (100µA - 10µA) = 90µA ✕RS
Since +1°C corresponds to 198.6µV, series resistance
contributes a temperature offset of:
Assume that the diode being measured has a series
resistance of 3Ω. The series resistance contributes an
offset of:
The effects of the ideality factor and series resistance
are additive. If the diode has an ideality factor of 1.002
and series resistance of 3Ω, the total offset can be cal-
culated by adding error due to series resistance with
error due to ideality factor:
1.36°C - 2.13°C = -0.77°C
for a diode temperature of +85°C.
In this example, the effect of the series resistance and
the ideality factor partially cancel each other.
Discrete Remote Diodes
When the remote-sensing diode is a discrete transistor,
its collector and base should be connected together.
Table 7 lists examples of discrete transistors that are
appropriate for use with the MAX6642.
The transistor must be a small-signal type with a rela-
tively 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 10µA, and at the lowest expected tempera-
ture, the forward voltage must be less than 0.95V at
100µA. Large power transistors must not be used. Also,
ensure that the base resistance is less than 100Ω. Tight
specifications for forward current gain (50 < ß <150, for
example) indicate that the manufacturer has good
process controls and that the devices have consistent
VBE characteristics.
Manufacturers of discrete transistors do not normally
specify or guarantee ideality factor. This is normally not
a problem since good-quality discrete transistors tend
to have ideality factors that fall within a relatively narrow
range. We have observed variations in remote tempera-
ture readings of less than ±2°C with a variety of dis-
crete transistors. Still, it is good design practice to
verify good consistency of temperature readings with
several discrete transistors from any manufacturer
under consideration.
ADC Noise Filtering
The integrating ADC used has good noise rejection for
low-frequency signals such as 60Hz/120Hz power-sup-
ply hum. In noisy environments, high-frequency noise
reduction is needed for high-accuracy remote mea-
surements. The noise can be reduced with careful PC
board layout and proper external noise filtering.
High-frequency EMI is best filtered at DXP with an
external 2200pF capacitor. Larger capacitor values can
be used for added filtering, but do not exceed 3300pF
because excessive capacitance can introduce errors
3 0 453 1 36Ω× °
Ω=+ ° ..
CC
90
198 6
0 453
µ
Ω
µ
°
=°
Ω
V
V
C
C
.
.
TT
n
nT
T
ACTUAL M NOMINAL M
M
=
=
=
1
1 008
1 002
1 00599
.
.
( . )
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
10 ______________________________________________________________________________________
MANUFACTURER MODEL NO.
Central Semiconductor (USA) CMPT3906
Rohm Semiconductor (USA) SST3906
Samsung (Korea) KST3906-TF
Siemens (Germany) SMBT3906
Zetex (England) FMMT3906CT-ND
Table 7. Remote-Sensor Transistor
Manufacturers
Note: Discrete transistors must be diode connected (base short-
ed to collector).
due to the rise time of the switched current source.
Nearly all noise sources tested cause the temperature
conversion results to be higher than the actual temper-
ature, typically by +1°C to +10°C, depending on the
frequency and amplitude (see the Typical Operating
Characteristics).
PC Board Layout
Follow these guidelines to reduce the measurement
error of the temperature sensors:
1) Connect the thermal-sense diode to the MAX6642
using two traces—one between DXP and the
anode, the other between the MAX6642’s GND and
the cathode. Do not connect the cathode to GND at
the sense diode.
2) Place the MAX6642 as close as is practical to the
remote thermal diode. In noisy environments, such
as a computer motherboard, this distance can be
4in to 8in (typ). This length can be increased if the
worst noise sources are avoided. Noise sources
include CRTs, clock generators, memory buses,
and ISA/PCI buses.
3) Do not route the thermal diode lines next to the
deflection coils of a CRT. Also, do not route the
traces across fast digital signals, which can easily
introduce a 30°C error, even with good filtering.
4) Route the thermal diode traces in parallel and in
close proximity to each other, away from any higher
voltage traces, such as +12VDC. Leakage currents
from PC board contamination must be dealt with
carefully since a 20MΩleakage path from DXP to
ground causes about +1°C error. If high-voltage
traces are unavoidable, connect guard traces to
GND on either side of the DXP trace (Figure 4).
5) Route through as few vias and crossunders as pos-
sible to minimize copper/solder thermocouple
effects.
6) When introducing a thermocouple, make sure that
both the thermal diode paths have matching ther-
mocouples. A copper-solder thermocouple exhibits
3µV/°C, and it takes about 200µV of voltage error at
DXP to cause a +1°C measurement error. Adding a
few thermocouples causes a negligible error.
7) Use wide traces. Narrow traces are more inductive
and tend to pick up radiated noise. The 10-mil
widths and spacing recommended in Figure 4 are
not absolutely necessary, as they offer only a minor
improvement in leakage and noise over narrow
traces. Use wider traces when practical.
8) Add a 47Ωresistor in series with VCC for best noise
filtering (see the Typical Operating Circuit).
9) Copper cannot be used as an EMI shield; only fer-
rous materials such as steel work well. Placing a
copper ground plane between the DXP-DXN traces
and traces carrying high-frequency noise signals
does not help reduce EMI.
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
shielded twisted pair like that 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 to DXP and GND and
the shield to GND. Leave the shield unconnected at the
remote diode.
For very long cable runs, the cable’s parasitic capaci-
tance often provides noise filtering, so the 2200pF
capacitor can often be removed or reduced in value.
Cable resistance also affects remote-sensor accuracy.
For every 1Ωof series resistance, the error is approxi-
mately 1/2°C.
Thermal Mass and Self-Heating
When sensing local temperature, this device is intend-
ed to measure the temperature of the PC board to
which it is soldered. The leads provide a good thermal
path between the PC board traces and the die. Thermal
conductivity between the die and the ambient air is
poor by comparison, making air temperature measure-
ments impractical. Because the thermal mass of the PC
board is far greater than that of the MAX6642, the
device follows temperature changes on the PC board
with little or no perceivable delay.
When measuring 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
MAX6642
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
______________________________________________________________________________________ 11
MINIMUM
10 mils
10 mils
10 mils
10 mils
THERMAL DIODE CATHODE/GND
THERMAL DIODE ANODE/DXP
GND
GND
Figure 4. Recommended DXP PC Traces
MAX6642
tracks the actual temperature within a conversion cycle.
When measuring temperature with discrete remote sen-
sors, smaller packages, such as SOT23s, yield the best
thermal response times. Take care to account for ther-
mal 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. For the local diode, the
worst-case error occurs when autoconverting at the
fastest rate and simultaneously sinking maximum cur-
rent at the ALERT output. For example, with VCC =
+5.0V, at an 8Hz conversion rate and with ALERT sink-
ing 1mA, the typical power dissipation is:
5.0V x 450µA + 0.4V x 1mA = 2.65mW
øJ-A for the 6-pin TDFN package is about +41°C/W, so
assuming no copper PC board heat sinking, the result-
ing temperature rise is:
∆T = 2.65mW x 41°C/W = +0.11°C
Even under nearly worst-case conditions, it is difficult to
introduce a significant self-heating error.
Chip Information
TRANSISTOR COUNT: 7744
PROCESS: BiCMOS
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
12 ______________________________________________________________________________________
Functional Diagram
MAX6642
MUX
REMOTE
LOCAL
ADC
2
CONTROL
LOGIC
SMBus
READ
WRITE
8
8
ADDRESS
DECODER
7
S
R
Q
DXP
SCLK
SDA
REGISTER BANK
COMMAND BYTE
REMOTE TEMPERATURE
LOCAL TEMPERATURE
ALERT THRESHOLD
ALERT RESPONSE
ADDRESS
ALERT
VCC
DIODE
FAULT
TOP VIEW
(BUMPS ON BOTTOM)
1
2
GND
3
6
5
4DXP
SDA
SCLK
VCC
TDFN
ALERT
MAX6642
Pin Configuration
MAX6642
±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13
© 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
6, 8, &10L, QFN THIN.EPS
PROPRIETARY INFORMATION
TITLE:
APPROVAL DOCUMENT CONTROL NO. REV.
2
1
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
21-0137 D
L
CL
C
SEMICONDUCTOR
DALLAS
A2
A
PIN 1
INDEX
AREA
D
E
A1
D2
b
E2 [(N/2)-1] x e
REF.
e
k
1N1
L
e
L
A
L
PIN 1 ID
C0.35
DETAIL A
e
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY
DOCUMENT CONTROL NO.APPROVAL
TITLE:
PROPRIETARY INFORMATION
REV.
2
2
COMMON DIMENSIONS
SYMBOL MIN. MAX.
A0.70 0.80
D2.90 3.10
E2.90 3.10
A1 0.00 0.05
L0.20 0.40
PKG. CODE
6
N
T633-1 1.50–0.10
D2
2.30–0.10
E2
0.95 BSC
e
MO229 / WEEA
JEDEC SPEC
0.40–0.05
b
1.90 REF
[(N/2)-1] x e
1.50–0.10 MO229 / WEEC 1.95 REF0.30–0.05
0.65 BSC
2.30–0.10T833-1 8
PACKAGE VARIATIONS
21-0137
0.25–0.05 2.00 REFMO229 / WEED-30.50 BSC1.50–0.10 2.30–0.1010T1033-1
0.25 MIN.
k
A2 0.20 REF.
D
SEMICONDUCTOR
DALLAS
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
WHAT'S NEW
PRODUCTS
SOLUTIONS
DESIGN
APPNOTES
SUPPORT
BUY
COMPANY
MEMBERS
MAX6642
Part Number Table
Notes:
See the MAX6642 QuickView Data Sheet for further information on this product family or download the MAX6642
full data sheet (PDF, 232kB).
1.
Other options and links for purchasing parts are listed at: http://www.maxim-ic.com/sales.2.
Didn't Find What You Need? Ask our applications engineers. Expert assistance in finding parts, usually within one
business day.
3.
Part number suffixes: T or T&R = tape and reel; + = RoHS/lead-free; # = RoHS/lead-exempt. More: See full
data sheet or Part Naming Conventions.
4.
* Some packages have variations, listed on the drawing. "PkgCode/Variation" tells which variation the product
uses.
5.
Part Number
Free
Sample
Buy
Direct
Package:
TYPE PINS SIZE
DRAWING CODE/VAR *
Temp
RoHS/Lead-Free?
Materials Analysis
MAX6642YATT98+T
-40C to +125C
RoHS/Lead-Free: Yes
MAX6642YATT90+T
-40C to +125C
RoHS/Lead-Free: Yes
MAX6642ATT94+
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633+2*
-40C to +125C
RoHS/Lead-Free: Yes
Materials Analysis
MAX6642ATT94+T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633+2*
-40C to +125C
RoHS/Lead-Free: Yes
Materials Analysis
MAX6642ATT92
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT94
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT96
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT98+
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633+2*
-40C to +125C
RoHS/Lead-Free: Yes
Materials Analysis
MAX6642ATT98
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT9A
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT9C
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT9E
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642YATT90+
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633+2*
-40C to +125C
RoHS/Lead-Free: Yes
Materials Analysis
MAX6642YATT98+
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633+2*
-40C to +125C
RoHS/Lead-Free: Yes
Materials Analysis
MAX6642ATT92+
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633+2*
-40C to +125C
RoHS/Lead-Free: Yes
Materials Analysis
MAX6642ATT90
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT90+
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633+2*
-40C to +125C
RoHS/Lead-Free: Yes
Materials Analysis
MAX6642ATT92-T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT94-T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT96-T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT98-T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT9A-T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT9C-T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT9E-T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
MAX6642ATT90+T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633+2*
-40C to +125C
RoHS/Lead-Free: Yes
Materials Analysis
MAX6642ATT98+T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633+2*
-40C to +125C
RoHS/Lead-Free: Yes
Materials Analysis
MAX6642ATT92+T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633+2*
-40C to +125C
RoHS/Lead-Free: Yes
Materials Analysis
MAX6642ATT90-T
THIN QFN (Dual);6 pin;3X3X0.8mm
Dwg: 21-0137I (PDF)
Use pkgcode/variation: T633-2*
-40C to +125C
RoHS/Lead-Free: No
Materials Analysis
Didn't Find What You Need?
CONTACT US: SEND US AN EMAIL
C opyright 2 007 by M axim Integrated P roducts, Dallas Semiconductor • Legal Notices • Privacy P olicy