STTS75 datasheet(20/39 Pages) STMICROELECTRONICS

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Functional description

STTS75

20/39

3.1.5

Hysteresis temperature register (THYS)

THYS register is a two-byte (16-bit) READ/WRITE register that stores the user-

programmable lower trip-point temperature for the thermal alarm in two’s complement

format (see Table 10). This register defaults to 75°C at power-up (i.e., 0100 1011 0000

0000).

The format of this register is the same as that of the temperature register. The 4 LSBs of the

THYS register are hardwired to zero, so data written to these bits is ignored. The MSB

position contains the sign bit for the digital temperature and Bit14 contains the temperature

MSB.

The resolution setting for the A/D conversion determines how many bits of the THYS register

are used by the thermal alarm. For example, for 9-bit conversions, the hysteresis

temperature is defined by the 9 MSBs of the THYS register, and all remaining bits are “Don’t

cares.”

3.2

Power-up default conditions

The STTS75 always powers up in the following default states:

●

Thermostat mode = comparator mode

●

Polarity = active-low

●

Fault tolerance = 1 fault (i.e., relevant bits set to '0' in the configuration register)

●

TOS = 80°C

●

THYS = 75°C

●

OSM = 0 (disabled)

●

Conversion resolution = 9-bit (i.e., RC0 = 0 and RC1 = 0 in the configuration register;

see Table 7 on page 18)

Note:

After power-up these conditions can be reprogrammed via the serial interface.

Table 10.

TOS and THYS register format

Bytes

MS byte

LS byte

Bits

MSB

THSB

TLSB

LSB

STTS75

TMSB TD

TD TD TD

9-bit

LSB

10-bit

LSB

11-bit

LSB

12-bit

LSB

Keys:

SB = two’s complement sign bit

TMSB = temperature MSB

TLSB = temperature LSB

TD = temperature data

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