MAXIM MAX6642 User Manual

General Description

The MAX6642 precise, two-channel digital temperature
sensor 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 transistor on the
die of a CPU, ASIC, GPU, or FPGA. The remote PN
junction can also be a discrete diode-connected small­signal 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 sin­gle-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 with an exposed pad.

Applications

Desktop Computers
Notebook Computers
Servers
Thin Clients
Test and Measurement
Workstations
Graphic Cards

Features

o Dual Channel: Measures Remote and Local

Temperature

o +0.25°C Resolution

o High Accuracy ±1°C (max) (Remote) and

±2°C (Local) from +60°C to +100°C

o Measures Remote Temperature Up to +150°C

o Programmable Overtemperature Alarm

Temperature Thresholds

o SMBus/I

2

C-Compatible Interface

o Tiny TDFN Package with Exposed Pad

MAX6642

±1°C, SMBus-Compatible Remote/Local

Temperature Sensor with Overtemperature Alarm

________________________________________________________________

Maxim Integrated Products

1

Ordering Information

19-2920; Rev 3; 10/09

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

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

T = Tape and reel.

*

EP = Exposed pad.

Pin Configuration and Functional Diagram appear at end of
data sheet.

SMBus is a trademark of Intel Corp.

PART TEMP RANGE PIN-PACKAGE

MAX6642ATT90-T -40°C to +125°C 6 TDFN-EP*

MAX6642ATT92-T -40°C to +125°C 6 TDFN-EP*

MAX6642ATT94-T -40°C to +125°C 6 TDFN-EP*

MAX6642ATT96-T -40°C to +125°C 6 TDFN-EP*

MAX6642ATT98-T -40°C to +125°C 6 TDFN-EP*

MAX6642ATT9A-T -40°C to +125°C 6 TDFN-EP*

MAX6642ATT9C-T -40°C to +125°C 6 TDFN-EP*

MAX6642ATT9E-T -40°C to +125°C 6 TDFN-EP*

0.1μF

2200pF

V

DXP

CC

MAX6642

47Ω

SDA

3.3V

10kΩ EACH

DATA

SCLK

ALERT

μP

GND

CLOCK

INTERRUPT TO μP

MAX6642

±1°C, SMBus-Compatible Remote/Local
Temperature Sensor with Overtemperature Alarm

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(V

CC

= +3.0V to +5.5V, TA = -40°C to +125°C, unless otherwise specified. Typical values are at V

CC

= +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
V

CC

...........................................................................-0.3V to +6V

DXP.............................................................-0.3V to (V

CC

+ 0.3V)

SCLK, SDA, ALERT ..................................................-0.3V to +6V

SDA, ALERT Current ...........................................-1mA to +50mA

Continuous Power Dissipation (T

A

= +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 V

Temperature Resolution

Remote Temperature Error V

Local Temperature Error V

Supply Sensitivity of Temperature
Error

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 t

Conversion Rate f

Remote-Diode Source Current I

ALERT

Output-Low Sink Current

Output-High Leakage Current VOH = V

CC

CONV

CONV

RJ

= 3.3V

CC

= 3.3V

CC

From stop bit to conversion completion 106 125 143 ms

High level 80 100 120

Low level 8 10 12

VOL = 0.4V 1

V

= 0.6V 4

OL

CC

3.0 5.5 V

0.25 °C

10 Bits

TRJ = +60°C to +100°C,

= +25°C to +85°C

T

A

TRJ = 0°C to +125°C -3.0 +3.0

T

= +125°C to +150°C -3.5 +3.5

RJ

TA = +60°C to +100°C -2.0 +2.0

= 0°C to +125°C -3.0 +3.0

T

A

-1.0 +1.0

±0.2 °C/V

8Hz

1µA

°C

°C

µA

mA

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 t

TIMEOUT

.

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)

(V

CC

= +3.0V to +5.5V, TA = -40°C to +125°C, unless otherwise specified. Typical values are at V

CC

= +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 V

Logic Input High Voltage V

Input Leakage Current I

Output Low Sink Current I

Input Capacitance C

SMBus TIMING (Note 2)

Serial Clock Frequency f

Bus Free Time Between STOP
and START Condition

START Condition Setup Time 4.7 µs

Repeat START Condition Setup
Time

START Condition Hold Time t

STOP Condition Setup Time t

Clock Low Period t

Clock High Period t

Data Setup Time t

Receive SCLK/SDA Rise Time t

Receive SCLK/SDA Fall Time t

Pulse Width of Spike Suppressed t

SMBus Timeout t

IL

IH

LEAK

OL

IN

SCLK

t

BUF

t

SU:STA

HD:STA

SU:STO

LOW

HIGH

HD:DAT

R

F

SP

TIMEOUT

VCC = 3.0V 2.2 V

VIN = GND or 5.5V -1 +1 µA

VOL = 0.6V 6 mA

(Note 3) 100 kHz

90% to 90% 50 ns

10% of SDA to 90% of SCLK 4 µs

90% of SCLK to 90% of SDA 4 µs

10% to 10% 4.7 µs

90% to 90% 4 µs

(Note 4) 250 µs

SDA low period for interface reset 20 28 40 ms

0.8 V

5pF

4.7 µs

1µs

300 ns

050ns

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

0 125

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 = 100mV

P-P

SQUARE WAVE

APPLIED TO V

CC

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
V

IN

= 100mV

P-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 volt­age and compute the temperature based on this volt­age. Both channels are automatically converted once
the conversion process has started, either in free-run­ning 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 chan­nel. 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 sec­ond. 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 config­uration byte register (Table 4). All data is retained in
memory, and the SMBus interface is active and listen­ing for SMBus commands. Standby mode is not a shut­down 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 tempera­ture register. The previous data is not changed and
remains available.

Supply-current drain during the 125ms conversion peri­od 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 stan­dard 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

2 GND Ground

3 DXP

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.

6 ALERT

—EP

Supply Voltage Input, +3V to +5.5V. Bypass V

CC

recommended but not required for additional noise filtering.

Combined Remote-Diode Current Source and ADC Input for Remote-Diode Channel. Place a 2200pF
capacitor between DXP and GND for noise filtering.

SMBus Alert (Interrupt) Output, Open Drain. ALERT asserts when temperature exceeds user-set limits. See
the

ALERT

Interrupts section.

Exposed Pad. Internally connected to GND. Connect to a PCB ground pad for optimal performance. Not
intended as an electrical connection point.

to GND with a 0.1µF capacitor. A 47Ω series resistor is

CC