LM3881: LM3881 with Max VIN 5.5V, Flag Output Gradually Drop

DK Wang

Part Number: LM3881

Hi,

We input 5.5V as both VIN and pull up voltage level at flag output for LM3881.

and we found the flag output will drop gradually after power up few minutes.

It will be normal again after power cycle.

The absolutly maximum Vin and EN is 6V.

Do you have any advice?

0 yihe over 2 years ago

Please share you schematics and provide a capture waveform including the VIN, EN, 1 FLAG and 3 FLAG output.

Regards

Yihe

0 DK Wang over 2 years ago in reply to yihe

0 DK Wang over 2 years ago in reply to DK Wang

We have changed pull up resistor from 100kohm to 10kohm.
If with 100kohm, the flag output level will be too low to enable LDOs.

0 yihe over 2 years ago in reply to DK Wang

10K or 100K pull up is not the concern.

But you can not tie the EN direct to the 5V.

You have to keep the EN below 1V before VCC is up 2.7V otherwise the behavior of the device is unpredictable.

Please either add a resistor divider on the EN or use a external control to drive EN.

Regards

Yihe

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