LM74-3EVAL National Semiconductor, LM74-3EVAL Datasheet - Page 8

• Manufacturer Part Number: LM74-3EVAL
• Manufacturer: National Semiconductor

Specifications of LM74-3EVAL

• Lead Free Status / Rohs Status: Not Compliant

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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 ∆Σ ADC (Delta-
Sigma Analog-to-Digital Converter). Compatibility of the
LM74’s three wire serial interface with SPI and MICROWIRE
allows simple communications with common microcontrol-
lers and processors. Shutdown mode can be used to opti-
mize current drain for different applications. A Manufacture’s/
Device ID register identifies the LM74 as National
Semiconductor product.
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 contents after POR but before completion of the
first temperature conversion.
The LM74 power-up default condition is continuous conver-
sion mode. After completion of the first full temperature
Static Supply Current vs Temperature (micro SMD)
Average Power-On Reset Voltage vs Temperature
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conversion, the register will contain temperature measure-
ment 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
temperature conversion. Note that bit D2 represents a com-
plete conversion flag. During POR it is low and, after the first
temperature conversion is complete, it goes high. This bit
can be polled to indicate when the POR data in the Tem-
perature 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
temperature 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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