PCT2075DP datasheet(14/37 Pages) NXP

14 / 37 page

PCT2075

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Product data sheet

Rev. 3 — 21 May 2013

14 of 37

NXP Semiconductors

PCT2075

I2C-bus Fm+ digital temperature sensor and thermal watchdog

The device temperature sensor powers up to measure temperature every 100 ms, with

Tidle = 00001 by default. For the PCT2075 with 11-bit accuracy, the ADC conversion is

about 28 ms. As a result, the PCT2075 will be idle for (100 ms

 28 ms) = 72 ms between

two temperature measurements.

7.5 OS output and polarity

The OS output is an open-drain output and its state represents results of the device

watchdog operation as described in Section 7.1. In order to observe this output state, an

external pull-up resistor is needed. The resistor should be as large as possible, up to

1.5 k

, to minimize the Temp reading error due to internal heating by the high OS sinking

current.

The OS output active state can be selected as HIGH or LOW by programming bit B2

(OS_POL) of register Conf: setting bit OS_POL to logic 1 selects OS active HIGH and

setting bit B2 to logic 0 sets OS active LOW. At power-up, bit OS_POL is equal to logic 0

and the OS active state is LOW.

7.6 OS comparator and interrupt modes

As described in Section 7.1, the device OS output responds to the result of the

comparison between register Temp data and the programmed limits, in registers Tos and

Thyst, in different ways depending on the selected OS mode: OS comparator or

OS interrupt. The OS mode is selected by programming bit B1 (OS_COMP_INT) of

setting to logic 0 selects the OS comparator mode. At power-up, bit OS_COMP_INT is

equal to logic 0 and the OS comparator is selected.

The main difference between the two modes is that in OS comparator mode, the OS

output becomes active when Temp has exceeded Tots and reset when Temp has dropped

below Thys, reading a register or putting the device into shutdown mode does not change

the state of the OS output; while in OS interrupt mode, once it has been activated either

by exceeding Tots or dropping below Thys, the OS output will remain active indefinitely until

reading a register, then the OS output is reset.

Temperature limits Tots and Thys must be selected so that Tots > Thys. Otherwise, the OS

output state will be undefined.

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