ADM1022ARQ-REEL7(2003) View Datasheet(PDF) - Analog Devices

Part Name

Description

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ADM1022ARQ-REEL7
(Rev.:2003)

Low-Cost PC Temperature Monitor and Fan Control ASIC

Analog Devices 

1

SCL

9

1

ADM1022

9

SDA

0

1

START BY

MASTER

0

1

1 A1

FRAME 1

SERIAL BUS ADDRESS

BYTE

A0 R/W

D7

ACK. BY

ADM1022

1

SCL

(CONTINUED)

D6 D5 D4 D3 D2 D1 D0

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

ADM1022

9

SDA (CONTINUED)

D7 D6 D5 D4 D3 D2 D1 D0

FRAME 3

DATA BYTE

ACK. BY STOP BY

ADM1022 MASTER

Figure 2a. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

1

9

1

9

SCL

SDA

0

1

START BY

MASTER

0

1

1 A1

FRAME 1

SERIAL BUS ADDRESS

BYTE

A0 R/W

D7

ACK. BY

ADM1022

D6 D5 D4 D3 D2 D1 D0

ACK. BY

ADM1022

FRAME 2

ADDRESS POINTER REGISTER BYTE

STOP BY

MASTER

Figure 2b. Writing to the Address Pointer Register Only

1

9

1

9

SCL

SDA

0

1

START BY

MASTER

0

1

1 A1 A0 R/W

D7 D6 D5 D4 D3 D2 D1

ACK. BY

ADM1022

FRAME 1

SERIAL BUS ADDRESS

BYTE

FRAME 2

DATA BYTE FROM ADM1022

Figure 2c. Reading Data from a Previously Selected Register

D0

NO ACK. STOP BY

BY MASTER MASTER

TEMPERATURE MEASUREMENT SYSTEM

Internal Temperature Measurement

The ADM1022 contains an on-chip bandgap temperature

sensor. The on-chip ADC performs conversions on the out-

put of this sensor and outputs the temperature data in 8-bit

twos complement format. The format of the temperature data

is shown in Table II.

External Temperature Measurement

The ADM1022 can measure the temperature of two external

diode sensors or diode-connected transistors, connected to Pins

9 and 10 or 11 and 12.

Pins 9 and 10 are a dedicated temperature input channel. The

default function of Pins 11 and 12 is the THERM input/output

and a general purpose logic input (GPI), but they can be config-

ured to measure a diode sensor by setting Bit 7 of the Configu-

ration Register to 1.

The forward voltage of a diode or diode-connected transistor,

operated at a constant current, exhibits a negative temperature

coefficient of about –2 mV/∞C. Unfortunately, the absolute value

of VBE, varies from device to device, and individual calibra-

tion is required to null this out, so the technique is unsuitable

for mass-production.

The technique used in the ADM1022 is to measure the change

in VBE when the device is operated at two different currents.

This is given by:

where:

DVBE = KT/q ¥ ln(N)

K is Boltzmann’s constant

q is charge on the carrier

T is absolute temperature in Kelvins

N is ratio of the two currents

REV. B

–9–

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