LM74CIMX-3 National Semiconductor, LM74CIMX-3 Datasheet - Page 8

• Manufacturer Part Number: LM74CIMX-3
• Description: IC TEMP SENSOR DGTL 8-SOIC
• Manufacturer: National Semiconductor

Specifications of LM74CIMX-3

• Function: Temp Monitoring System (Sensor)
• Topology: ADC (Sigma Delta), Register Bank
• Sensor Type: Internal
• Sensing Temperature: -55°C ~ 150°C
• Output Type: MICROWIRE™, SPI™
• Output Alarm: No
• Output Fan: No
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -55°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LM74CIMX-3TR

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Typical Performance Characteristics
1.0 Functional Description
The LM74 temperature sensor incorporates a band-gap type
temperature sensor and 12-bit plus sign ΔΣ ADC (Delta-Sig-
ma Analog-to-Digital Converter). Compatibility of the LM74's
three wire serial interface with SPI and MICROWIRE allows
simple communications with common microcontrollers and
processors. Shutdown mode can be used to optimize current
drain for different applications. A Manufacture's/Device ID
register identifies the LM74 as National Semiconductor prod-
uct.
1.1 POWER UP AND POWER DOWN
When the supply voltage is less than about 1.6V (typical), the
LM74 is considered powered down. The LM74 always powers
up in a known state. When the supply voltage rises above
1.6V (typical), an internal Power-On Reset (POR) occurs and
the temperature register will then contain a value of 1111
1111 0000 00XX, where XX indicates undefined values. See
Section 1.5.2 for a diagram of the Temperature Regisiter con-
tents after POR but before completion of the first temperature
conversion.
Static Supply Current vs Temperature (micro SMD)
Average Power-On Reset Voltage vs Temperature
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The LM74 power-up default condition is continuous conver-
sion mode. After completion of the first full temperature con-
version, the register will contain temperature measurement
data in bits D15 (the temperature data MSB) through D3 (the
temperature data LSB). Bit D2 will be fixed high; bits D1 and
D0 are undefined. See Section 1.5.3 for a diagram of the
Temperature Regisiter contents after the first complete tem-
perature conversion. Note that bit D2 represents a complete
conversion flag. During POR it is low and, after the first tem-
perature conversion is complete, it goes high. This bit can be
polled to indicate when the POR data in the Temperature
Register has been replaced with valid temperature data.
After the first conversion, and any subsequent conversions,
the value in the temperature register does not change until
the completion of the next conversion, at which time the tem-
perature register is updated with the latest temperature value.
1.2 SERIAL BUS INTERFACE
The LM74 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-
Static Supply Current vs Temperature (SO-8)
Temperature Error (SO-8)
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