REV. 0

ADM1022

–9–

R/

W

0

SCL

SDA

1

0

1

1

A1

A0

D7

D6

D5

D4

D3

D2

D1

D0

ACK. BY

ADM1022

START BY

MASTER

19

1

ACK. BY

ADM1022

9

D7

D6

D5

D4

D3

D2

D1

D0

ACK. BY

ADM1022

STOP BY

MASTER

1

9

SCL (CONTINUED)

SDA (CONTINUED)

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

FRAME 3

DATA BYTE

Figure 11a. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

R/

W

0

SCL

SDA

1

0

1

1

A1

A0

D7

D6

D5

D4

D3

D2

D1

D0

ACK. BY

ADM1022

START BY

MASTER

19

1

ACK. BY

ADM1022

9

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

STOP BY

MASTER

Figure 11b. Writing to the Address Pointer Register Only

R/

W

0

SCL

SDA

1

0

1

1

A1

A0

D7

D6

D5

D4

D3

D2

D1

D0

NO ACK.

BY MASTER

START BY

MASTER

19

1

ACK. BY

ADM1022

9

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

DATA BYTE FROM ADM1022

STOP BY

MASTER

Figure 11c. Reading Data from a Previously Selected Register

TEMPERATURE MEASUREMENT SYSTEM

Internal Temperature Measurement

The ADM1022 contains an on-chip bandgap temperature sen-

sor. The on-chip ADC performs conversions on the output of

this sensor and outputs the temperature data in 8-bit twos comple-

ment 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

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

This is given by:

where:

K is Boltzmann’s constant

q is charge on the carrier

T is absolute temperature in Kelvins

N is ratio of the two currents

Figure 12 shows the input signal conditioning used to mea-

sure the output of an external temperature sensor. This figure

shows the external sensor as a substrate transistor, provided

for temperature monitoring on some microprocessors, but it

could equally well be a discrete transistor.