Datasheet

LM95245
www.ti.com 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 ΔV
be
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.
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