STLED325 datasheet(27/62 Pages) STMICROELECTRONICS

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STLED325

Functional description

Doc ID 17576 Rev 1

27/62

While the interrupt is being read by the MCU and a new GPIO or key data comes in, no new

interrupt is generated but the register for GPIO and KEY data is updated so that the MCU

does not miss the new KEY and GPIO data.

3.14

Ready

The STLED325 supports cutting-off power to the main board for standby operation for good

power management. STBY will be set to high when the READY transitions from high to low.

During a cold boot up or wake up from standby, if the READY pin stays low, the STLED325

will assert the STBY when the guard timer has finished counting down to 0.

When the READY drops to a low, MUTE goes high immediately and soon after (2µs

minimum) the STBY is asserted.

In the normal mode of operation, when READY is a high, the STBY is asserted only when

the guard timer is enabled and has finished counting down to 0. This is meant to put the

system into stand-by as the READY pin was stuck at high and the guard timer register was

not cleared before it finished counting down to 0. It is advised to disable the guard timer

during normal operation.

3.15

Mute

The MUTE pin will be set to logic high to mute the audio output before power is cut to the

host processor. In wake up mode, the MUTE pin will be set to logic low to enable the audio

output immediately after the high assertion of the READY pin. In general, MUTE follows

READY pin with an inverted polarity. This pin is used to prevent pop-up sound during power-

up and power-down states.

3.16

GPIO

The STLED325 supports 2 additional GPIOs that can be configured as inputs or outputs. As

an input, the GPIO can be used to interface to a sensor or a switch or key and as an output,

the GPIO can be used to drive individual indicator LEDs.

3.17

Power sense circuits

The STLED325 has a built-in power sense circuit which detects power failures and

automatically switches to the battery or super-cap supply when a power failure occurs. The

energy needed to sustain the SRAM and clock operations can be supplied by small lithium

button supply or a super-cap when a power failure occurs. When operating from the battery

or super-cap, all the inputs and outputs are driven to a known state (generally L).

STLED325 Datasheet(PDF) 27 Page - STMicroelectronics