Datasheet

Product data sheet Rev. 6.1 — 6 February 2015 12 of 37

NXP Semiconductors

LM75B

Digital temperature sensor and thermal watchdog

7.7 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 B4 and B3 (OS_F_QUE[1:0]) in register Conf.

Notice that the programmed data and the fault queue value are not the same. Table 14

shows the one-to-one relationship between them. At power-up, fault queue data = 0 and

fault queue value = 1.

7.8 Shutdown mode

The device operation mode is selected by programming bit B0 (SHUTDOWN) of register

Conf. Setting bit SHUTDOWN to logic 1 will put the device into shutdown mode. Resetting

bit SHUTDOWN to logic 0 will return the device to normal mode.

In shutdown mode, the device draws a small current of approximately 1.0 A and the

power dissipation is minimized; the temperature conversion stops, but the I

C-bus

interface remains active and register write/read operation can be performed. When the

shutdown is set, the OS output will be unchanged in comparator mode and reset in

interrupt mode.

7.9 Power-up default and power-on reset

The LM75B always powers-up in its default state with:

• Normal operation mode

• OS comparator mode

• T

th(ots)

= 80 C

• T

hys

= 75 C

• OS output active state is LOW

• Pointer value is logic 00 (Temp)

When the power supply voltage is dropped below the device power-on reset level of

approximately 1.0 V (POR) for over 2 s and then rises up again, the device will be reset

to its default condition as listed above.

Table 14. Fault queue table

Fault queue data Fault queue value

OS_F_QUE[1] OS_F_QUE[0] Decimal

001

012

104

116