STDS75 Datasheet, PDF (19/37 Pages) STMicroelectronics – Digital temperature sensor and thermal watchdog

STDS75
Functional description
3.1.5
Note:
Hysteresis temperature register (T_HYS)
T_HYS 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 9). 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 T_HYS 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 T_HYS
Register are used by the thermal alarm. For example, for 9-bit conversions, the hysteresis
temperature is defined by the 9 MSBs of the T_HYS Register, and all remaining bits are “Don’t
cares.”
Table 9.
Bytes
T_OS and T_HYS register format
MS Byte
LS Byte
MSB
THSB
Bits
15 14 13 12 11 10 9 8 7
TLSB
LSB
6
5
4 321 0
STDS75
SB
TMSB TD
TD
TD
TD TD TD
9-bit
LSB
10-bit
LSB
11-bit
LSB
12-bit
LSB
0
0
0
0
Keys: SB =Two’s complement Sign Bit
TMSB =Temperature MSB
TLSB =Temperature LSB
TD =Temperature Data
These are comparable formats to the DS75 and LM75.
3.2
Note:
Power-up default conditions
The STDS75 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)
● T_OS = 80°C
● T_HYS = 75°C
● Register pointer = 00 (Temperature register)
● Conversion resolution = 9-bit (i.e., RC0 = 0 and RC1 = 0 in the Configuration register;
see Table 7 on page 17)
After power-up these conditions can be reprogrammed via the serial interface.
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