ADT7488A

http://onsemi.com

11

temperature difference. Unless there are two

thermocouples with a big temperature differential

between them, thermocouple voltages should be much

less than 200 mV.

ADT7488A.

inches, the use of a twisted pair cable is recommended.

This works for distances of about 6 feet to 12 feet.

twisted pair cables, such as Belden #8451 microphone

cables. Connect the twisted pair cable to D+ and D−

and the shield to GND, close to the ADT7488A. Leave

the remote end of the shield unconnected to avoid

ground loops.

Because the measurement technique uses switched

current sources, excessive cable and/or filter capacitance

can affect the measurement. When using long cables, the

filter capacitor can be reduced or removed. Cable resistance

can also introduce errors. A 1

W series resistance introduces

about 0.5

°C error.

Temperature Offset

As CPUs run faster, it is more difficult to avoid high

frequency clocks when routing the D+ and D− tracks around

a system board. Even when the recommended layout

guidelines are followed, there may still be temperature

errors, attributed to noise being coupled onto the D+ and D−

lines. High frequency noise generally has the effect of

producing temperature measurements that are consistently

too high by a specific amount. The ADT7488A has

temperature offset command codes of 0xe0 and 0xe1

through which a desired offset can be set. By doing a

one−time calibration of the system, the offset caused by

system board noise can be calculated and nulled by

specifying it in the ADT7488A. The offset is automatically

added to every temperature measurement. The maximum

offset is

±128°C with 0.25°C resolution. The offset format

is the same as the temperature data format; 16−bit, twos

complement notation, as shown in Table 11. The offset

should be programmed in little endian format, that is, LSB

before MSB. The offset value is also returned in little endian

format when read.

Application Schematic

A typical application circuit for the ADT7488A is shown

in Figure 18. The ADT7488A can be used in conjunction

with the ADP3192 controller to monitor the CPU power.

The result is a complete thermal and power monitor for the

CPU.

Figure 18. ADT7488A Application Schematic: CPU Thermal− and Power−Supply Monitoring

1

GND

2

D1+

3

D1–

4

D2+

5

SST

SST

R = 1k

C = 10nF

10

7

ADT7488A

2N3905

NPN

CPU

POWER

MONITORING

THERMAL DIODE

DRIVERS

ADP3120A

ADP3192

W

CPU POWER

CONTROLLER

ORDERING INFORMATION

Device Order Number*

Package Type

Package Option

ADT7488AARMZ−RL

10−Lead MSOP

RM−10

3000 Tape & Reel

ADT7488AARMZ−RL7

1000 Tape & Reel

†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging

Specifications Brochure, BRD8011/D.

*These are Pb−Free packages.