Specifications

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60 Control and Automation Solutions Guide

or one that is integrated on the die

of another IC. Microprocessors, eld-

programmable gate arrays (FPGAs), and

ASICs often include one or more sensing

transistors, usually called thermal diodes,

similar to the one shown in Figure 4.

There is an important advantage to

remote temperature sensors: they allow

you to monitor more than one hot spot

with a single IC. A basic single remote

sensor like the MAX6642 in Figure 4 can

monitor two temperatures: its own and

an external temperature. The external

location can be on the die of a target IC,

or a hot spot on a board that it monitors

with a discrete transistor. Some remote

sensors monitor as many as seven

external temperatures. Thus, eight

locations, consisting of ICs and board hot

spots, are monitored from a single chip.

Consider the MAX6602 as an example.

This temperature sensor has four remote

diode inputs so it can monitor the

temperatures of a pair of FPGAs with

integrated thermal diodes, two board

hot spots using discrete transistors, and

the temperature of the board at the

MAX6602’s location. Both the MAX6602

and the MAX6642 achieve ±1°C accuracy

when reading external thermal diodes.

+3.3V

DXP

SMBCLK

SMBDATA

ALERT

SMBus/I

C SERIAL

INTERFACE

(TO MASTER)

4.7kΩ

GND

CPU, ASIC,

FPGA

ON-CHIP

PN JUNCTION

2200pF

MAX6642

Figure 4. A remote temperature sensor, the MAX6642, monitors the temperature of a sensing transistor (or thermal diode) on

the die of an external IC.