STLED325 datasheet(17/62 Pages) STMICROELECTRONICS

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STLED325

Functional description

Doc ID 17576 Rev 1

17/62

3.10.2

Entering standby mode

The STLED325 controls the power to the main board using the STBY pin. During normal

operation, the STBY pin is a low level which externally controls a Power MOS switch to

enable power to the main board. The STLED325 asserts the STBY pin to a high when any

one of the following conditions occur:

– Processor fails to respond by enabling the READY pin within 10s upon first power-up

(cold boot up)

– Guard timer counts down to 0s

– Processor makes the READY pin to low (can happen in various conditions such as

user presses STBY key on front panel, STBY key on remote control, etc).

Figure 6.

Power down condition (normal behavior)

– Guard timer can be kept on during normal condition when READY is high (depending

on the user).

– In this condition, the guard timer can be disabled or enabled. If the guard timer is

enabled, the timer needs to be cleared before the programmed count of the timer is

reached. If the programmed count is reached, the STBY will be asserted.

– It is advisable not to enable the guard timer during normal operation.

READY

STBY

2a) Power-down condition (normal behavior )

MUTE

READY

STBY

2b) Power-down condition (abnormal behavior of processor )

MUTE

In this case the READY remains high and as long as

READY is high, the MUTE is low and STBY is low.

2 us

READY continues to remain high

Guard timer is not required here

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