ADM1021A

–12–

REV. D

7. For really long distances (up to 100 feet), use shielded twisted

pair such as Belden #8451 microphone cable. Connect the

twisted pair to D+ and D– and the shield to GND close to

the ADM1021A. Leave the remote end of the shield uncon-

nected to avoid ground loops.

Because the measurement technique uses switched current sources,

excessive cable and/or filter capacitance can affect the measure-

ment. When using long cables, the filter capacitor may be

reduced or removed.

Cable resistance can also introduce errors. 1

Ω series resistance

introduces about 1

°C error.

APPLICATION CIRCUITS

Figure 8 shows a typical application circuit for the ADM1021A,

using a discrete sensor transistor connected via a shielded,

twisted pair cable. The pull-ups on SCLK, SDATA, and

ALERT

are required only if they are not already provided elsewhere in

the system.

The SCLK and SDATA pins of the ADM1021A can be inter-

faced directly to the SMBus of an I/O chip. Figure 9 shows how

the ADM1021A might be integrated into a system using this

type of I/O controller.

STBY

SCLK

SDATA

ALERT

ADD0

ADD1

GND

D+

D–

0.1 F

ALL 10k

3.3V

TO CONTROL

CHIP

SET TO REQUIRED

ADDRESS

IN

OUT

I/O

C1*

SHIELD

2N3904

*C1 IS OPTIONAL

ADM1021A

Figure 8. Typical Application Circuit

USB USB

PROCESSOR

DISPLAY

SYSTEM BUS

DISPLAY

CACHE

SYSTEM

MEMORY

GMCH

FWH

(FIRMWARE HUB)

ADM1021A

D–

D+

ALERT

SCLK

SDATA

SUPER

I/O

SMBUS

PCI BUS

PCI SLOTS

2 USB PORTS

CD ROM

HARD

DISK

2 IDE PORTS

ICH

I/O CONTROLLER

HUB

Figure 9. Typical System Using ADM1021A