G781 datasheet(7/14 Pages) ETC

7 / 14 page

Ver: 1.0

Oct 02, 2002

TEL: 886-3-5788833

http://www.gmt.com.tw

Global Mixed-mode Technology Inc.

G781

If software standby command is received while a con-

version is in progress, the conversion cycle is trun-

cated, and the data from that conversion is not latched

into either temperature reading register. The previous

data is not changed and remains available.

Supply-current drain during the 125ms conversion

period is always about 320µA. Slowing down the con-

version rate reduces the average supply current (see

Typical Operating Characteristics). In between con-

versions, the instantaneous supply current is about

25µA due to the current consumed by the conversion

rate timer. In standby mode, supply current drops to

about 3µA. At very low supply voltages (under the

power-on-reset threshold), the supply current is higher

due to the address pin bias currents. It can be as high

as 100µA, depending on ADD0 and ADD1 settings.

SMBus Digital Interface

From a software perspective, the G781 appears as a

set of byte-wide registers that contain temperature

data, alarm threshold values, or control bits, A stan-

dard SMBus 2-wire serial interface is used to read

temperature data and write control bits and alarm

threshold data.

Each A/D channel within the device responds to the

same SMBus slave address for normal reads and

writes.

The G781 employs four standard SMBus protocols:

Write Byte, Read Byte, Send Byte, and Receive Byte

(Figure 3). The shorter Receive Byte protocol allows

quicker transfers, provided that the correct data regis-

ter was previously selected by a Read Byte instruction.

Use caution with the shorter protocols in multi-master

systems, since a second master could overwrite the

command byte without informing the first master.

The temperature data format is 11bits plus sign in

twos-complement form for remote channel, with each

data bit representing 0.125°C (Table 2,Table 3),

transmitted MSB first.

Table 2. Temperature Data Format

(Two’s-Complement)

DIGITAL OUTPUT

DATA BITS

TEMP.

(°C)

SIGN

MSB

LSB

EXT

+127.875

111

1111

111

+126.375

111

1110

011

+25.5

001

1001

100

+1.75

000

0001

110

+0.5

000

0000

100

+0.125

000

0000

001

-0.125

111

1111

111

-1.125

111

1110

111

-25.5

110

0110

100

-55.25

100

1000

110

-65.000

011

1111

000

Table 3. Extended Temperature Data Format

EXTENDED

RESOLUTION

DATA BITS

0.000°C

0000 0000

0.125°C

0010 0000

0.250°C

0100 0000

0.375°C

0110 0000

0.500°C

1000 0000

0.625°C

1010 0000

0.750°C

1100 0000

0.875°C

1110 0000

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