1.0 Functional Description
The LM95235 is a temperature sensor that measures Local
and Remote temperature zones. The LM95235 uses a
temperature sensing method. A differential voltage, repre-
senting temperature, is digitized using a Sigma-Delta analog
to digital converter. TruTherm Technology allows the
LM95235 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 Section
3.0 Application Hints. The LM95235 is compatible with the
serial SMBus version 2.0 two-wire serial interface.
The LM95235 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 Con-
figuration 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 Re-
mote 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 set-
tings for each measured temperature that triggers T_CRIT
and/or OS pins:
The following table describes the limit register mapping to
the T_CRIT and/or OS pins:
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 in-
crease the resolution of the temperature reading. If the filter
is enabled the filtered readings are used for TCRIT and OS
comparisons. The LM95235 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
LM95235’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 the LM95235 Register table. 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 al-
lowing 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.
1.1 CONVERSION SEQUENCE
In the power-up default state the LM95235 takes a maximum
of 1 second to convert the Local Temperature, Remote Tem-
perature, and to update all of its registers. Only during the
conversion process is the Busy bit (D7) in Status Register 1
(02h) high. These conversions are addressed in a round-
robin sequence. The conversion rate may be modified by the
Conversion Rate bits found in the Conversion Rate Register
(R/W: 04h/0Ah). When the conversion rate is modified a
delay is inserted between conversions, the actual maximum
conversion time remains at 72 ms. Different conversion rates
will cause the LM95235 to draw different amounts of supply
current as shown in Figure 1.
1.2 POWER-ON-DEFAULT STATES
LM95235 always powers up to these known default states.
The LM95235 remains in these states until after the first
Command Register set to 00h
Conversion Rate register defaults to 02h (1 second).
Local Temperature set to 0˚C until the end of the first
Remote Diode Temperature set to 0˚C until the end of
the first conversion
Remote OS limit default is 55h (85 ˚C).
Local Shared and TCRIT limit default is 55h (85 ˚C).
FIGURE 1. Conversion Rate Effect on Power Supply