Datasheet

LM95221

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SNIS134B –MAY 2004–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 LM95221. The maximum resistance of the pull-up to provide a 2.1V high

level, based on LM95221 specification for High Level Output Current with the supply voltage at 3.0V, is

82kΩ(5%) or 88.7kΩ(1%).

DIODE FAULT DETECTION

The LM95221 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−, V

or D+ is floating, the Remote

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.

COMMUNICATING with the LM95221

The data registers in the LM95221 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 LM95221 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 LM95221 will always include the address byte and the command byte. A write to any register

requires one data byte.

Reading the LM95221 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

read from the LM95221), 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 LM95221 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). It takes the LM95221 66 ms to measure the temperature of the remote diodes and internal

diode. 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

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.

Product Folder Links: LM95221