LM95235 datasheet(12/25 Pages) NSC

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1.0 Functional Description (Continued)

1.6 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

LM95235. The maximum resistance of the pull-up to provide

a 2.1V high level, based on LM95235 specification for High

Level Output Current with the supply voltage at 3.0V, is

82 k

Ω (5%) or 88.7 kΩ (1%).

1.7 T_CRIT OUTPUT AND TCRIT LIMIT

The LM95235’s T_CRIT pin is an active-low open-drain out-

put that is triggered when the local and/or the remote tem-

perature conversion is above the limits defined by the Re-

mote and/or Local Limit registers. The state of the T_CRIT

pin will return to the HIGH state when both the Local and

Remote temperatures are below the values programmed

into the Limit Registers less the value in the Common Hys-

teresis Register. Additionally, if the remote temperature ex-

ceeds the value in the Remote TCRIT Limit Register the

Status Bit for Remote TCRIT (RTCRIT), in Status Register 1,

is set to 1. In the same way if the local temperature exceeds

the value in the Local Shared OS and TCRIT Limit Register

the Status Bit for the Shared Local OS and TCRIT (LOC) bit

in Status Register 1 is set to 1.The T_CRIT output and the

Status Register flags are updated after every Local and

Remote temperature conversion. See Figure 4

1.8 OS OUTPUT AND OS LIMIT

The LM95235’s OS/A0 pin is selected as an OS digital

output as described in Section 1.3. As an OS pin, it is

activated whenever the local and/or remote temperature

conversion is above the limits defined by the Limit registers.

If the remote temperature exceeds the value in the Remote

OS Limit Register the Status Bit for Remote OS (ROS) in

Status Register 1 is set to 1. In the same way if the local

temperature exceeds the value in the Local Shared OS and

TCRIT Limit Register the Status Bit for the Shared Local OS

and TCRIT (LOC) bit in Status Register 1 is set to 1. The

state of the T_CRIT pin output will return to the HIGH state

when both the Local and Remote temperatures are below

the values programmed into the Limit Registers less the

value in the Common Hysteresis Register. The OS output

and the Status Register flags are updated after every Local

and Remote temperature conversion. See Figure 5.

1.9 DIODE FAULT DETECTION

The LM95235 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−,

DD or D+ is floating, the Remote Temperature reading is

–128.000 ˚C if signed format is selected and +255.875 ˚C if

unsigned format is selected. In addition, the Status Register

1 bit D2 is set.

1.10 COMMUNICATING with the LM95235

The data registers in the LM95235 are selected by the

Command Register. At power-up the Command Register is

set to “00”, the location for the Read Local Temperature

was set to. Each data register in the LM95235 falls into one

of four types of user accessibility:

Read only

Write only

Write/Read same address

Write/Read different address

A Write to the LM95235 will always include the address byte

and the command byte. A write to any register requires one

data byte.

Reading the LM95235 can take place either of two ways:

If the location latched in the Command Register is cor-

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

isters because that will be the data most frequently read

from the LM95235), then the read can simply consist of

an address byte, followed by retrieving the data byte.

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 LM95235 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 consecu-

20174913

FIGURE 4. T_CRIT Comparator Temperature Response

Diagram

20174915

FIGURE 5. OS Temperature Response Diagram

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