Temperature

Digital Output

Binary

Hex

−0.25˚C

1111 1111 1100 0000

FFE0h

−1˚C

1111 1111 0000 0000

FF00h

−25˚C

1110 0111 0000 0000

E700h

−55˚C

1100 1001 0000 0000

C900h

1.5 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

82k

Ω(5%) or 88.7kΩ(1%).

1.6 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

–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.

1.7 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 cor-

rect (most of the time it is expected that the Command

Register will point to one of the Read Temperature Reg-

isters because that will be the data most frequently 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 tempera-

ture 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.

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