STCN75 Datasheet, PDF (17/35 Pages) STMicroelectronics – Digital temperature sensor and thermal watchdog

STCN75
Functional description
3.1.3
Temperature register
The Temperature register is a two-byte (16-bit) “Read only” register (see Table 7). Digital
temperatures from the T-to-D converter are stored in the Temperature register in two’s
complement format, and the contents of this register are updated each time the T-to-D
conversion is finished.
The user can read data from the Temperature register at any time. When a T-to-D
conversion is completed, the new data is loaded into a comparator buffer to evaluate fault
conditions, and will update the Temperature register if a read cycle is not ongoing. The
STCN75 is continuously evaluating fault conditions regardless of READ or WRITE activity
on the bus. If a READ is ongoing, the previous temperature will be read. The readable
temperature will be updated upon the completion of the next T-to-D conversion that is not
masked by a read cycle.
All unused bits following the digital temperature will be zero. The MSB position of the
Temperature register always contains the sign bit for the digital temperature, and Bit 14
contains the temperature MSB. All bits in the Temperature register default to zero at power-
up.
Table 7.
Bytes
Temperature register format⁽¹⁾
HS byte
LS byte
MSB
TMSB
TLSB
LSB
Bits
15
14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
STCN75
TD8
(S)
TD7 TD TD TD TD TD TD TD0
(TMSB) 6 5 4 3 2 1 (TLSB)
x
x
x
x
x
x
x
3.1.4
Keys: S = Two’s complement sign bit
TMSB = temperature MSB
TLSB = temperature LSB
TDx = temperature data bits
1. These are comparable formats to the LM75.
Over-limit temperature register (T_OS)
T_OS register is a two-byte (16-bit) READ/WRITE register that stores the user-programmable
upper trip-point temperature for the thermal alarm in two’s complement format (see Table 8
on page 18). This register defaults to 80°C at power-up (i.e., 0101 0000 0000 0000).
The format of the T_OS register is identical to that of the Temperature register. The MSB
position contains the sign bit for the digital temperature and Bit14 contains the temperature
MSB.
For 9-bit conversions, the trip-point temperature is defined by the 9 MSBs of the T_OS
register, and all remaining bits are “Don’t cares” (x).
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