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MAX1617A

Remote/Local Temperature Sensor with SMBus Serial Interface

Maxim Integrated 

MAX1617A

Remote/Local Temperature Sensor

with SMBus Serial Interface

through the one-shot command, despite the RUN/STOP

bit being high.

Activate hardware standby mode by forcing the STBY pin

low. In a notebook computer, this line may be connected

to the system SUSTAT# suspend-state signal.

The STBY pin low state overrides any software conversion

command. If a hardware or software standby command 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 register. The previ-

ous data is not changed and remains available.

Supply-current drain during the 125ms conversion period

is always about 450μA. Slowing down the conversion rate

reduces the average supply current (see Typical Operating

Characteristics). 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 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 MAX1617A 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 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 MAX1617A 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 7 bits plus sign in two’s

complement form for each channel, with each data bit repre-

senting 1°C (Table 2), transmitted MSB first. Measurements

are offset by +1/2°C to minimize internal rounding errors;

for example, +99.6°C is reported as +100°C.

Write Byte Format

S

ADDRESS

WR

7 bits

Slave Address: equivalent

to chip-select line of a

3-wire interface

ACK

COMMAND

ACK

8 bits

Command Byte: selects which

register you are writing to

DATA

ACK

P

8 bits

1

Data Byte: data goes into the register set

by the command byte (to set thresholds,

configuration masks, and sampling rate)

Read Byte Format

S ADDRESS WR

7 bits

Slave Address:

equivalent to

chip-select line

ACK

COMMAND ACK

8 bits

Command Byte:

selects which

register you are

reading from

Send Byte Format

S ADDRESS WR

7 bits

ACK

COMMAND ACK P

8 bits

Command Byte: sends

command with no data,

usually used for

one-shot command

S = Start condition

P = Stop condition

Shaded = Slave transmission

/// = Not acknowledged

Figure 3. SMBus Protocols

S ADDRESS RD ACK DATA ///

P

7 bits

8 bits

Slave Address:

repeated due to change

in data-flow direction

Data Byte: reads from

the register set by the

command byte

Receive Byte Format

S ADDRESS RD

7 bits

ACK DATA ///

P

8 bits

Data Byte: reads data from

the register commanded by

the last Read Byte or Write

Byte transmission; also used

for SMBus Alert Response

return address

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