LM95235EVAL/NOPB National Semiconductor, LM95235EVAL/NOPB Datasheet - Page 9

• Manufacturer Part Number: LM95235EVAL/NOPB
• Description: BOARD EVALUATION LM95235
• Manufacturer: National Semiconductor
• Series: PowerWise®, TruTherm®r

Specifications of LM95235EVAL/NOPB

• Sensor Type: Temperature
• Sensing Range: -40°C ~ 125°C
• Interface: SMBus (2-Wire/I²C)
• Sensitivity: ±1°C
• Voltage - Supply: 3 V ~ 3.6 V
• Embedded: Yes, MCU, 8-Bit
• Utilized Ic / Part: LM95235
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM95235EVAL

1.0 Functional Description
The LM95235 is a temperature sensor that measures Local
and Remote temperature zones. The LM95235 uses a ΔV
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 en-
abled, the local temperature is compared to the user-pro-
grammable 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 Configu-
ration Register 1. The comparison result can also be read
back from Status Register 1. If enabled, the remote temper-
ature 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 ta-
ble describes the default temperature settings for each mea-
sured 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 perfor-
mance 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 LM95235 may be placed in low power consumption
(Standby) mode by setting the STOP/RUN bit found in Con-
figuration 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 con-
tained 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
Output Pin
T_CRIT
OS
Output Pin
T_CRIT
OS
TCRIT Limit
Remote OS
Remote
Remote
Limit
Remote, °C
110
85
Local Shared OS/TCRIT
Local Shared OS/TCRIT
Local, °C
Local
Limit
Limit
85
85
be
9
LM95235 Register table. The lower 2-bits of the remote tem-
perature 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 Re-
mote 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 Con-
version 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 conver-
sion time remains at 72 ms. Different conversion rates will
cause the LM95235 to draw different amounts of supply cur-
rent 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 con-
version.
1.
2.
3.
4.
5.
6.
7.
8.
FIGURE 1. Conversion Rate Effect on Power Supply
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
conversion
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).
Remote TCRIT limit default is 6Eh (110 °C).
Remote Offset High and Low bytes default to 00h.
Current
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