D7

D6

D5

D4

D3

D2

D1

D0

1

9

1

9

Ack

by

LM95231

Start by

Master

R/W

Frame 1

Serial Bus Address Byte

Frame 2

Command Byte

Ack by

LM95231

SMBCLK

SMBDAT

A5

A3

A2

A0

A6

A4

A1

Stop

by

Master

LM95231

www.ti.com

SNIS139E – FEBRUARY 2005 – REVISED MARCH 2013

SMBDAT OPEN-DRAIN OUTPUT

The SMBDAT output is an open-drain output and does not have internal pull-ups. A “high” level will not be

observed on this pin until pull-up current is provided by some external source, typically a pull-up resistor. Choice

of resistor value depends on many system factors but, in general, the pull-up resistor should be as large as

possible without effecting the SMBus desired data rate. This will minimize any internal temperature reading

errors due to internal heating of the LM95231. The maximum resistance of the pull-up to provide a 2.1V high

level, based on LM95231 specification for High Level Output Current with the supply voltage at 3.0V, is 82k

Ω

(5%) or 88.7k

Ω (1%).

1.6 DIODE FAULT DETECTION

The LM95231 is equipped with operational circuitry designed to detect fault conditions concerning the remote

diodes. In the event that the D+ pin is detected as shorted to GND, D

Temperature reading is –128.000 °C if signed format is selected and +255.875 if unsigned format is selected. In

addition, the appropriate status register bits RD1M or RD2M (D1 or D0) are set. When TruTherm mode is active

the condition of diode short of D+ to D

− will not be detected. Connecting a 2N3904 transistor with TruTherm

mode active may cause a detection of a diode fault.

1.7 COMMUNICATING with the LM95231

The data registers in the LM95231 are selected by the Command Register. At power-up the Command Register

is set to “00”, the location for the Read Local Temperature Register. The Command Register latches the last

location it was set to. Each data register in the LM95231 falls into one of four types of user accessibility:

1. Read only

2. Write only

3. Write/Read same address

4. Write/Read different address

A Write to the LM95231 will always include the address byte and the command byte. A write to any register

requires one data byte.

Reading the LM95231 can take place either of two ways:

1. If the location latched in the Command Register is correct (most of the time it is expected that the Command

Register will point to one of the Read Temperature Registers because that will be the data most frequently

read from the LM95231), then the read can simply consist of an address byte, followed by retrieving the data

byte.

2. If the Command Register needs to be set, then an address byte, command byte, repeat start, and another

address byte will accomplish a read.

The data byte has the most significant bit first. At the end of a read, the LM95231 can accept either acknowledge

or No Acknowledge from the Master (No Acknowledge is typically used as a signal for the slave that the Master

has read its last byte). When retrieving all 11 bits from a previous remote diode temperature measurement, the

master must insure that all 11 bits are from the same temperature conversion. This may be achieved by reading

the MSB register first. The LSB will be locked after the MSB is read. The LSB will be unlocked after being read. If

the user reads MSBs consecutively, each time the MSB is read, the LSB associated with that temperature will be

locked in and override the previous LSB value locked-in.

Figure 7. Serial Bus Write to the Internal Command Register

Copyright © 2005–2013, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Links: LM95231