LM70

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SNIS112G – JUNE 2000 – REVISED MARCH 2013

FUNCTIONAL DESCRIPTION

The LM70 temperature sensor incorporates a band-gap type temperature sensor and 10-bit plus sign

ΔΣ ADC

(Delta-Sigma Analog-to-Digital Converter). Compatibility of the LM70'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 ID register identifies the LM70 as a

TI product.

POWER UP AND POWER DOWN

The LM70 always powers up in a known state. The power up default condition is continuous conversion mode.

Immediatly after power up the LM70 will output an erroneous code until the first temperature conversion has

completed.

When the supply voltage is less than about 1.6V (typical), the LM70 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.

SERIAL BUS INTERFACE

The LM70 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 communication 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 TRISTATE. 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 edge of SC. The remainder of

the data will be clocked out by the falling edge of SC. Once the 14 bits of data (one sign bit, ten temperature bits

and 3 high bits) are transmitted the SI/O line will go into TRI-STATE. CS can be taken high at any time during

the transmit phase. If CS is brought low in the middle of a conversion the LM70 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 periods. CS can remain low for 32 SC cycles. The

LM70 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. A zero in any location will take the

LM70 out of shutdown. The following codes only should be transmitted to the LM70:

•

00 hex (normal operation)

•

01 hex (normal operation)

•

03 hex (normal operation)

•

07 hex (normal operation)

•

0F hex (normal operation)

•

1F hex (normal operation)

•

3F hex(normal operation)

•

7F hex(normal operation)

•

FF hex (Shutdown, transmit manufacturer's ID)

any others may place the part into a Test Mode. Test Modes are used by TI to thoroughly test the function of the

LM70 during production testing. Only eight bits have been defined above since only the last eight transmitted,

before CS is taken HIGH, are detected by the LM70

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:

•

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.

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