LM95245

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SNIS148G – OCTOBER 2007 – REVISED MARCH 2013

FUNCTIONAL DESCRIPTION

The LM95245 is a temperature sensor that measures Local and Remote temperature zones. The LM95245 uses

a

ΔVbe temperature sensing method. A differential voltage, representing temperature, is digitized using a Sigma-

Delta analog to digital converter. TruTherm BJT (Transistor) Beta Compensation Technology allows the

LM95245 to accurately sense the temperature of a thermal diode found on die fabricated using a sub-micron

process. For more information on TruTherm Technology see Applications Hints . The LM95245 is compatible

with the serial SMBus version 2.0 two-wire serial interface.

The LM95245 has OS and TCRIT open-drain digital outputs that indicate the state of the local and remote

temperature readings when compared to user-programmable limits. If enabled, the local temperature is

compared to the user-programmable Local Shared OS and TCRIT Limit Register (Default Value = 85°C). The

comparison result can trigger the T_CRIT pin and/or the OS pin depending on the settings of the Local TCRIT

Mask and OS Mask bits found in Configuration Register 1. The comparison result can also be read back from

Status Register 1. If enabled, the remote temperature is compared to the user-programmable Remote TCRIT

Limit Register (Default Value = 110°C), and the Remote OS Limit Register (Default Value = 85°C) values. The

comparison result can trigger the T_CRIT pin and/or the OS pin depending on the settings of Configuration

Register 1. The following table describes the default temperature settings for each measured temperature that

triggers T_CRIT and/or OS pins:

Output Pin

Remote, °C

Local, °C

T_CRIT

110

85

OS

85

85

The following table describes the limit register mapping to the T_CRIT and/or OS pins:

Output Pin

Remote

Local

T_CRIT

Remote TCRIT Limit

Local Shared OS/TCRIT Limit

OS

Remote OS Limit

Local Shared OS/TCRIT Limit

The T_CRIT and OS outputs are open-drain, active low.

The remote temperature readings support a programmable digital filter. Based on the settings in Configuration

Register 2 a digital filter can be turned on to improve the noise performance of the remote temperature as well as

to increase the resolution of the temperature reading. If the filter is enabled the filtered readings are used for

TCRIT and OS comparisons. The LM95245 may be placed in low power consumption (Standby) mode by setting

the STOP/RUN bit found in Configuration Register 1. In the Standby mode, the LM95245’s SMBus interface

remains active while all circuitry not required is turned off. In the Standby mode the host can trigger one round of

conversions by writing to the One-Shot Register. The value written into this register is not kept. Local and

Remote temperatures will be converted once and the T_CRIT and OS pins will reflect the comparison results

based on this set of conversions results.

All the temperature readings are in 16-bit left-justified word format. The 10-bit plus sign local temperature reading

is contained in two 8-bit registers: Local Temp MSB and Local Temp LSB Registers. The remote temperature

supports both a 13-bit unsigned and a 12-bit plus sign format. These readings are available in their

corresponding registers as described in Table 8. The lower 2-bits of the remote temperature reading will contain

temperature information only if the digital filter is enabled. If the digital filter is disabled, these two bits will read

back 0.

The signed and unsigned remote temperature readings are available simultaneously in separate registers,

therefore allowing both negative temperatures and temperatures 128°C and above to be measured.

All Limit Registers support unsigned temperature format with 1°C LSb resolution. The Local Shared TCRIT and

OS Limit Register is 7 bits for limits between 0°C and 127°C. The Remote Temperature TCRIT and OS Limit

Registers are 8 bits each for limits between 0°C and 255°C.

Copyright © 2007–2013, Texas Instruments Incorporated

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