LM71CIMF National Semiconductor, LM71CIMF Datasheet - Page 8

• Manufacturer Part Number: LM71CIMF
• Description: Temperature Sensor IC
• Manufacturer: National Semiconductor

Specifications of LM71CIMF

• Peak Reflow Compatible (260 C): No
• Ic Function: Temperature Sensor IC
• Supply Voltage Max: 5.5V
• Leaded Process Compatible: No
• Supply Voltage Min: 2.65V
• Operating Temperature Min: -40°C
• Package / Case: 5-SOT-23
• Temperature Sensor Function: Temp Sensor
• Interface Type: 3-Wire/SPI
• Output Type: Digital
• Resolution: 13+SignBit
• Package Type: SOT-23
• Operating Temperature (min): -40C
• Operating Temperature (max): 150C
• Operating Temperature Classification: Automotive
• Operating Supply Voltage (typ): 3.3/5V
• Operating Supply Voltage (max): 5.5V
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Typical Performance Characteristics
1.0 Functional Description
The LM71 temperature sensor incorporates a temperature
sensor and 13-bit plus sign ΔΣ ADC (Delta-Sigma Analog-to-
Digital Converter). Compatibility of the LM71's three wire
serial interface with SPI and MICROWIRE allows simple com-
munications with common microcontrollers and processors.
Shutdown mode can be used to optimize current drain for dif-
ferent applications. A Manufacture's/Device ID register iden-
tifies the LM71 as National Semiconductor product.
1.1 POWER UP AND POWER DOWN
The LM71 always powers up in a known state. The power up
default condition is continuous conversion mode. Immediately
after power up the LM71 will output an erroneous code until
the first temperature conversion has completed.
When the supply voltage is less than about 1.6V (typical), the
LM71 is considered powered down. As the supply voltage
rises above the nominal 1.6V power up threshold, the internal
registers are reset to the power up default state described
above.
1.2 SERIAL BUS INTERFACE
The LM71 operates as a slave and is compatible with SPI or
MICROWIRE bus specifications. Data is clocked out on the
falling edge of the serial clock (SC), while data is clocked in
on the rising edge of SC. A complete transmit/receive com-
munication will consist of 32 serial clocks. The first 16 clocks
comprise the transmit phase of communication, while the
second 16 clocks are the receive phase.
When CS is high SI/O will be in TRI-STATE. Communication
should be initiated by taking chip select (CS) low. This should
not be done when SC is changing from a low to high state.
Once CS is low the serial I/O pin (SI/O) will transmit the first
bit of data. The master can then read this bit with the rising
Static Supply Current vs. Temperature
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8
edge of SC. The remainder of the data will be clocked out by
the falling edge of SC. CS can be taken high at any time during
the transmit phase. If CS is brought low in the middle of a
conversion the LM71 will complete the conversion and the
output shift register will be updated after CS is brought back
high.
The receive phase of a communication starts after 16 SC pe-
riods. CS can remain low for 32 SC cycles. The LM71 will read
the data available on the SI/O line on the rising edge of the
serial clock. Input data is to an 8-bit shift register. The part will
detect the last eight bits shifted into the register. The receive
phase can last up to 16 SC periods. All ones must be shifted
in order to place the part into shutdown. All zeros must be
shifted in order to place the LM71 into continuous conversion
mode. Only the following codes should be transmitted to the
LM71:
•
•
Another code may place the part into a test mode. Test modes
are used by National Semiconductor to thoroughly test the
function of the LM71 during production testing. Only eight bits
have been defined above since only the last eight transmitted
are detected by the LM71, before CS is taken HIGH.
The following communication can be used to determine the
Manufacturer's/Device ID and then immediately place the part
into continuous conversion mode. With CS continuously low:
•
•
•
•
•
Note that 300 ms will have to pass for a conversion to com-
plete before the LM71 actually transmits temperature data.
00 hex for continuous conversion
FF hex for shutdown
Read 16 bits of temperature data
Write 16 bits of data commanding shutdown
Read 16 bits of Manufacture's/Device ID data
Write 8 to 16 bits of data commanding Conversion Mode
Take CS HIGH.
Temperature Error
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