Datasheet
LM75B All information provided in this document is subject to legal disclaimers. © NXP B.V. 2015. All rights reserved.
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
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
output becomes active when Temp has exceeded T
th(ots)
and reset when Temp has
dropped below T
hys
, 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 T
th(ots)
or dropping below T
hys
, the OS output will remain active
indefinitely until reading a register, then the OS output is reset.
Temperature limits T
th(ots)
and T
hys
must be selected so that T
th(ots)
> T
hys
. 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 50 +25.0 C
0 0000 0001 001 1 +0.5 C
0 0000 0000 000 0 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