THMC10

REMOTE/LOCAL TEMPERATURE MONITOR

WITH SMBus INTERFACE

SLIS089 – DECEMBER 1999

13

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

external temperature sensor connections (DXP and DXN)

The DXP and DXN terminals are used to sense the remote temperature of either a microprocessor die or a

simple diode-connected transistor. Referring to Figure 6, the THMC10 has an internal state machine controlling

an analog MUX, an 8-bit A/D converter, plus 10-

µA and 90-µA nominal current sources. The analog MUX

switches between the THMC10’s internal temperature sensor and the external one connected to DXP and DXN.

This allows the use of only one 8-bit A/D converter, eliminating errors which would be present when using two

and subtracts the difference between the two sampled values. It then scales the resulting

into a 2s complement, 8-bit binary format that is available over the SMBus interface (see Table 2). By using two

different current levels and a single diode-connected transistor to measure the

canceled, and therefore no calibration is needed.

8–Bit A/D

Converter

DXP

Substrate

On-Chip Temp

Sensor

GND

VDD

10

µ

90

µA

Control

State

Machine

Analog

MUX

Remote

Die

Substrate

DXN

Remote

Temp

Sensor

(CPU)

THMC10

Front End

A

Figure 6. Temperature Measurement Block Diagram

external temperature sensor diagnostics (DXP and DXN)

The THMC10 provides diagnostic capabilities to allow detection of either an open external sensor or a shorted

If the interrupt mask bit is not set in the configuration register, it asserts the ALERT terminal low and sets bit two

in the status register. When DXP is shorted to DXN, the THMC10 reports 0

°C for the external temperature and

no fault is reported. If any of the above conditions exceed a temperature limit, then a temperature limit error is

also indicated in the status register if the interrupt mask bit is not set.