STLM75 datasheet(12/37 Pages) STMICROELECTRONICS

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Operation

STLM75

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2.2

Thermal alarm function

The STLM75 thermal alarm function provides user-programmable thermostat capability and

allows the STLM75 to function as a standalone thermostat without using the serial interface.

The OS output is the alarm output. This signal is an open drain output, and at power-up, this

pin is configured with active-low polarity by default.

2.3

Comparator mode

In comparator mode, each time a temperature-to-digital (T-to-D) conversion occurs, the new

digital temperature is compared to the value stored in the TOS and THYS registers. If a fault

tolerance number of consecutive temperature measurements are greater than the value

stored in the TOS register, the OS output will be asserted.

For example, if the FT1 and FT0 bits are equal to “10” (fault tolerance = 4), four consecutive

temperature measurements must exceed TOS to activate the OS output. Once the OS

output is active, it will remain active until the first time the measured temperature drops

below the temperature stored in the THYS register.

When the thermostat is in comparator mode, the OS can be programmed to operate with

any amount of hysteresis. The OS output becomes active when the measured temperature

exceeds the TOS value a consecutive number of times as defined by the FT1 and FT0 fault

tolerance (FT) bits in the configuration register. The OS then stays active when the

temperature falls below the value stored in THYS register for a consecutive number of times

as defined by the fault tolerance bits (FT1 and FT0). Putting the device into shutdown mode

does not clear OS in comparator mode.

STLM75 Arkusz danych(PDF) 12 Page - STMicroelectronics