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TPS54561-heavy load

Bruce Chien

Prodigy 60 points

Hi,

I have a project use TPS54661, Vin=6~50V, Vout=5.3V, Iout=3A, and had a heavy load issue, when I used under 15Vin and Iout 3A caused Vout unstable.The waveform as below.

What do I need to modify the circuit , please advise?

over 10 years ago

0 JohnTucker over 10 years ago

TI__Guru**** 191445 points

That does not look like instability. It looks more like restart. The restart time looks like almost 50 msec...way too long. Your SS time with 10nF should be around 4 msec. I don't see anything particularly wrong with your schematic. Can I look at your PCB layout? Also can I see the SW node waveform and VIN waveform? Zoom in and trigger on the falling edge of Vout, maybe 10usec/div.

0 Bruce Chien over 10 years ago in reply to JohnTucker

Prodigy 60 points

Hi John,

1. Yellow : Vin

2. Green : SW node

3. Blue : Vout

Am I need add snubber on schottky diode ?

0 JohnTucker over 10 years ago in reply to Bruce Chien

TI__Guru**** 191445 points

You have missed the trigger point. That waveform shows normal operation.

0 Praveen GD over 10 years ago

TI__Guru 57737 points

Hi Bruce,

I suspect the current limit of the power supply. When you reduce the input voltage, it draws more current to maintain the output power.

Can you check the current limit set on your power supply and make sure that it is not the cause.

Regards,

Praveen GD

0 JohnTucker over 10 years ago in reply to Praveen GD

TI__Guru**** 191445 points

That would be a possibility. We will need to see the waveform at the point where Vout collapses.