SE95_7

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 07 — 2 September 2009

6 of 27

NXP Semiconductors

SE95

Ultra high accuracy digital temperature sensor and thermal watchdog

7.2 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

Ω, 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

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

setting 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.

7.3 OS comparator and interrupt modes

As described in Section 7.1, the 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 OS_COMP_INT of register Conf: setting bit

OS_COMP_INT to logic 1 selects the OS interrupt mode, and 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

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

reading a register or putting the device into shutdown mode occurs, then the OS output is

reset.

output state will be undefined.

7.4 OS fault queue

Fault queue is defined as the number of faults that must occur consecutively to activate

the OS output. It is provided to avoid false tripping due to noise. Because faults are

determined at the end of data conversions, fault queue is also defined as the number of

consecutive conversions returning a temperature trip. The value of fault queue is

selectable by programming the two bits OS_F_QUE[1:0] in register Conf. Notice that the

programmed data and the fault queue value are not the same. Table 3 shows the

one-to-one relationship between them. At power-up, fault queue data = 00 and fault queue

value = 1.

Table 3.

Fault queue table

Fault queue data

Fault queue value

OS_F_QUE[1]

OS_F_QUE[0]

Decimal

001

012

104

116