SS8018 datasheet(7/14 Pages) SSC

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SS8018

Low-Power Standby Mode

Standby mode disables the ADC and reduces the sup-

ply-current drain to about 10µA. Enter standby mode by

forcing high to the RUN /STOP bit in the configuration

byte register. Software standby mode behaves such that

all data is retained in memory, and the SMB interface is

alive and listening for reads and writes.

Software standby mode is not a shutdown mode. With

activity on the SMBus, extra supply current is drawn

(see Typical Operating Characteristics). In software

standby mode, the G781 can be forced to perform A/D

conversions via the one-shot command, despite the

RUN

/STOP bit being high. If software standby com-

mand is received while a conversion is in progress, the

conversion cycle is truncated, and the data from that

conversion is not latched into either temperature reading

available.

Supply-current drain during the 125ms conversion pe-

riod is always about 320µA. Slowing down the conver-

sion rate reduces the average supply current (see Typi-

cal Operating Characteristics). In between conversions,

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 ad-

dress pin bias currents. It can be as high as 100µA, de-

pending on ADD0 and ADD1 settings.

SMBus Digital Interface

From a software perspective, the SS8018 appears as a

set of byte-wide registers that contain temperature data,

alarm threshold values, or control bits, A standard

SMBus 2-wire serial interface is used to read tempera-

ture 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 SS8018 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 register

was previously selected by a Read Byte instruction. Use

caution with the shorter protocols in multi-master sys-

tems, since a second master could overwrite the com-

mand 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), trans-

mitted 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

Rev.2.01 6/06/2003

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