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TC77-5.0MOA

Thermal Sensor with SPI Interface

Microchip Technology 

3.1 Temperature Data Format

A 13-bit two’s complement digital word is used to rep-

resent the temperature. The Least Significant Bit (LSb)

is equal to 0.0625°C. Note that the last two LSb bits (Bit

0 and 1) are tri-stated and are represented as a logic ‘1’

in the table. Bit 2 is set to logic ‘1’ after the completion

of the first temperature conversion following a power-

up or voltage reset event.

TABLE 3-1: TC77 OUTPUT

Temperature

Binary

MSB / LSB

Hex

+125°C

+25°C

+0.0625°C

0°C

0011 1110 1000 0111 3E 87h

0000 1100 1000 0111 0B 87h

0000 0000 0000 1111 00 0Fh

0000 0000 0000 0111 00 07h

-0.0625°C

1111 1111 1111 1111 FF FFh

-25°C

1111 0011 1000 0111 F3 87h

-55°C

1110 0100 1000 0111 E4 87h

An over-temperature condition can be determined by

reading only the first few Most Significant Bits (MSb) of

the temperature data. For example, the microprocessor

could read only the first four bits of the Temperature

register in order to determine that an over-temperature

condition exists.

3.2 Power-Up And Power-Down

The TC77 is in the Continuous Temperature Conver-

sion mode at power-up. The first valid temperature con-

version will be available approximately 300 ms (refer to

“Temperature to Bits Converter” section listed in the DC

characteristics table) after power-up. Bit 2 of the Tem-

perature register is set to a logic ‘1’ after the completion

of the first temperature conversion following a power-

up or voltage reset event. Bit 2 is set to logic ‘0’ during

the time needed to complete the first temperature con-

version. Thus, the status of bit 2 can be monitored to

indicate the completion of the first temperature conver-

sion.

A supply voltage lower than 1.6V (typ.) is considered a

power-down state for the TC77. The device will reset

itself and continue its normal Continuous Conversion

mode of operation when the supply voltage rises above

the nominal 1.6V. A minimal supply voltage of 2.7V is

required in order to ensure proper operation of the

device.

TC77

3.3 Serial Bus Interface

The serial interface consists of the Chip Select (CS),

Serial Clock (SCK) and Serial Data (SI/O) signals. The

TC77 meets the SPI and MICROWIRE bus specifica-

tions, with the serial interface designed to be compati-

ble with the Microchip PIC® family of microcontrollers.

The CS input is used to select the TC77 when multiple

devices are connected to the serial clock and data

lines. The CS line is also used to synchronize the data,

which is written to, or read from, the device when CS is

equal to a logic ‘0’ voltage. The SCK input is disabled

when CS is a logic ‘1’. The falling edge of the CS line

initiates communication, while the rising edge of CS

completes the communication.

The SCK input is provided by the external microcon-

troller and is used to synchronize the data on the SI/O

line. The Temperature and Manufacturer ID registers

are read only while the Configuration register is a read/

write register.

Figure 3-2 provides a timing diagram of a read opera-

tion of the Temperature register. Communication with

the TC77 is initiated when the CS goes to a logic ‘0’.

The Serial I/O signal (SI/O) then transmits the first bit of

data. The microcontroller serial I/O bus master clocks

the data in on the rising edge of SCK. The falling edge

of SCK is then used to clock out the rest of the data.

After 14 bits of data (thirteen temperature bits and Bit 2)

have been transmitted, the SI/O line is then tri-stated.

Note that CS can be taken to a logic ‘1’ at any time dur-

ing the data transmission if only a portion of the temper-

ature data information is required. The TC77 will

complete the conversion, and the output shift register

will be updated, if CS goes to the inactive state while in

the middle of a conversion.

Figure 3-3 provides a timing diagram of a multi-byte

communication operation consisting of a read of the

Temperature Data register, followed by a write to the

Configuration register. The first 16 SCK pulses are

used to transmit the TC77's temperature data to the

microcontroller. The second group of 16 SCK pulses

are used to receive the microcontroller command to

place the TC77 either in Shutdown or Continuous Tem-

perature Conversion mode. Note that the TC77 is in the

Continuous Temperature Conversion mode at power-

up.

The data written to the TC77’s Configuration register

should be either all 0’s or all 1’s, corresponding to

either the Continuous Temperature Conversion or

Shutdown mode, respectively. The TC77 is in Shut-

down mode when Bits C0 to C7 are all equal to 1’s. The

TC77 will be in the Continuous Conversion mode if a ‘0’

in any bit location from C0 to C7 is written to the

Configuration register.

 2002-2012 Microchip Technology Inc.

DS20092B-page 9

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