FS5908

Rev. 1.2

12/22

13.2.1

ALARM Pin and arm_inv Setup

arm_inv bit in the control register decides the ALARM pin output mode (please refer to the diagram on previous

page), the relationship between arm_inv and ALARM is as follow:

arm_inv is 0:

In comparison operation mode, if the temperature is lower than the lower bound setup, ALARM

is logic standard 1; if the temperature is higher than the upper bound setup, ALARM is logic

standard 0.

In interrupt operation mode, ALARM in general situation is logic standard 1; if sending out the

interrupt signal, ALARM is logic standard 0.

arm_inv is 1:

In comparison operation mode, if the temperature is lower than the lower bound setup, ALARM

is logic standard 0; if the temperature is higher than the upper bound setup, ALARM is logic

standard 1.

In interrupt operation mode, ALARM in general situation is logic standard 0; if send out the

interrupt signal, ALARM is logic standard 1.

In comparison mode, ALARM output can be used to enable cool fan or emergency system, close or reduce

system clock. FS5908 in comparison mode w ill not reset ALARM status when entering stand-by mode.

In interrupt mode, the arm_inv should be set to 0 no matter that it is applied to overcool warning or overheat

warning.

Once detected the temperature exceeded the upper bound value, ALARM will send out the interrupt signal

immediately. In the mean time, to read any FS5908 register via I2C interface will clear ALARM interrupt signal.

ALARM will send out the interrupt signal again until detected the temperature being lower than the lower bound

value. It is the same to clear the interrupt signal via reading the register. FS5908 in interrupt mode will reset

ALARM output when entering stand-by mode.

13.2.2

ALARM Output

ALARM output pin outputs by open-drain (see below diagram), which without inner circuit promotion design. It

will not generate logic high standard unless offering the additional current promotion from external (promotive

resistor generally). The select of promotive resistor depends on the system.

Alarm Generator

based on

T

ALARM

Req

Ron

Vp

In above diagram, when current I flows, MOS power consumption is:

Pav =I