STDS75 Datasheet, PDF(10/37 Page) STMicroelectronics – Digital temperature sensor and thermal watchdog

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STDS75 Datasheet, PDF (10/37 Pages) STMicroelectronics – Digital temperature sensor and thermal watchdog

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Operation

STDS75

Note:

After each temperature measurement and analog-to-digital conversion, the STDS75 stores

the temperature as a 16-bit twoâs complement number in the 2-byte temperature register

(see Table 8: Temperature register format). The most significant Bit (S, Bit 15) indicates if

the temperature is positive or negative:

â for positive numbers S = 0, and

â for negative numbers S = 1.

The most recently converted digital measurement can be read from the temperature register

at any time. Since temperature conversions are performed in the background, reading the

temperature register does not affect the operation in progress.

Bits 3 through 0 of the temperature register are hardwired to logic '0.' When the STDS75 is

configured for 12-bit resolution, the 12MSBs (Bits 15 through 4) of the temperature register

will contain temperature data. For 11-bit resolution, the 11MSBs (Bits 15 through 5) of the

temperature register will contain data, and Bit 4 will read out as logic '0.' For 10-bit

resolution, the 10MSbs (Bits 15 through 6) will contain data, and for 9-bit resolution the

9MSbs (Bits 15 through 7) will contain data and all unused LSBs will contain '0s.'

Table 3 on page 15 gives examples of 12-bit resolution digital output data and the

corresponding temperatures. The data is compared to the values in the TOS and THYS

registers, and then the OS/INT is updated based on the result of the comparison and the

operating mode. The number of TOS and THYS bits used during the thermostat comparison

is equal to the conversion resolution set by the FT1 and FT0 Bits in the Configuration

by the thermostat comparator. The alarm fault tolerance is controlled by the FTI and FTO

Bits in the Configuration register. They are used to set up a fault queue. This prevents false

tripping of the OS/INT pin when the STDS75 is used in a noisy environment (see Table 2 on

page 14).

The active state of the OS/INT output can be changed via the Polarity (POL) Bit in the

Configuration register. The power-up default is active-low.

If the user does not wish to use the thermostat capabilities of the STDS75, the OS/INT

output should be left floating.

If the thermostat is not used, the TOS and THYS registers can be used for general storage of

system data.

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