LM27762: LDO current limit

Kuramochi Tadahiko

Guru 28715 points

Part Number: LM27762

Hi,

I would like to know LDO current limit operation.

Could you show me the behavior or waveform during current limit?

Best Regards,

Kuramochi

over 7 years ago

0 Chris Glaser over 7 years ago

TI__Guru**** 150950 points

Hi Kuramochi-san,

Which LDO are you asking about, the positive one or negative?

What is the concern with the current limit operation?

0 Kuramochi Tadahiko over 7 years ago in reply to Chris Glaser

Guru 28715 points

Chris-san,

Thank you for your reply.

>Which LDO are you asking about, the positive one or negative?

Positive one.

>What is the concern with the current limit operation?

My customer says that output current is 3A at the moment during start up.

Best Regards,

Kuramochi

0 Chris Glaser over 7 years ago in reply to Kuramochi Tadahiko

TI__Guru**** 150950 points

Hi Kuramochi-san,

Thank you for your reply.

Is the 3A the actual load or just the inrush to the output caps? There will be some big voltage drop across the pass transistor.

Here is the waveform of a short on Vout+

0 Kuramochi Tadahiko over 7 years ago in reply to Chris Glaser

Guru 28715 points

Chris-san,

Thank you for your information.

3A current is inrush(120us).

They observe the current before output capacitor during startup.

Current limit cannot prevent inrush current because it is a moment.

Is it correct?

Best Regards,

Kuramochi

0 Chris Glaser over 7 years ago in reply to Kuramochi Tadahiko

TI__Guru**** 150950 points

Hi Kuramochi-san,

If I understand correctly, you have a 3A current for about 120 usec which occurs as the +Vout ramps up to its voltage?

The waveform above shows that the current limit does respond very quickly (<< 120 usec).

0 Kuramochi Tadahiko over 7 years ago in reply to Chris Glaser

Guru 28715 points

Hi Chris-san,

Thank you for your help.
I send you waveforms directly.
Could you check it?

Best Regards,
Kuramochi

0 Chris Glaser over 7 years ago in reply to Kuramochi Tadahiko

TI__Guru**** 150950 points

Yes, I had a look at your waveforms and they are ok.

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LM27762: LDO current limit