LM75BDP datasheet(11/37 Pages) NXP

11 / 37 page

LM75B

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Product data sheet

Rev. 6.1 — 6 February 2015

11 of 37

NXP Semiconductors

LM75B

Digital temperature sensor and thermal watchdog

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

200 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 Tth(ots) 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 Tth(ots) or dropping below Thys, the OS output will remain active

indefinitely until reading a register, then the OS output is reset.

Temperature limits Tth(ots) and Thys must be selected so that Tth(ots) > Thys. Otherwise, the

OS output state will be undefined.

Table 13.

Tos and Thyst limit data and value

11-bit binary

(two’s complement)

Hexadecimal value

Decimal value

Value

0 1111 1010

0FA

250

+125.0

C

0 0011 0010

032

+25.0

C

0 0000 0001

001

+0.5

C

0 0000 0000

000

0.0

C

1 1111 1111

1FF

1

0.5 C

1 1100 1110

1CE

50

25.0 C

1 1001 0010

192

110

55.0 C

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