tps56528: Cannot start up with high output capacitor value

Chris Swinson

Part Number: TPS56528
Other Parts Discussed in Thread: LM2576, TPS54628, LMR23625, LMR23630, TPS54334

I am using the tps56528 demo board, I have changed output to 5V, and change inductor to a flat wound type. I am getting almost 95% efficiency with about 12 mV ripple pretty awesome!

My problem is that the equipment that is powered by this regulator cannot start up on its own, generally the equipment has 4700uF (and higher) capacitance, and the TPS circuit cannot start up with this value output capacitor.

I assume that initial power up is tripping the overcurrent sense circuit ? Is there anything that can be done to combat this problem?

I have also looked at a couple of other switch mode ICs, and they suffer from the same problem. Currently I'm using the simple switcher LM2576 and this is more than happy to function with virtually any value output capacitor.

over 7 years ago

0 Andy Chen over 7 years ago

TI__Mastermind 33355 points

Hi

TPS56528 has fixed 1ms soft start time, it may not workable with too big Cout up to 4700uF.
can you try other part with external adjustable soft start chip?

0 Chris Swinson over 7 years ago in reply to Andy Chen

Intellectual 360 points

I found the tps54628 is similar, so going to try that as it has a SS pin.

0 Chris Swinson over 7 years ago in reply to Chris Swinson

Intellectual 360 points

The adjustable Soft Start feature worked just fine. I can start up easily with 4,700 now.

Though I am really struggling to find similar devices with 12V output. SOIC would be ideal with soft start. Though I cannot seem to find anything at all other than the LMR23625 which doesnt have SS.

I am using the LM2576-12 currently, but looking for something SMT which I can actually solder to, which is more efficient than the LM2576. Any suggestions ?

0 Andy Chen over 7 years ago in reply to Chris Swinson

TI__Mastermind 33355 points

Hi,

What's the input voltage range? and load current? do you need 5V or 12V output?

0 Chris Swinson over 7 years ago in reply to Andy Chen

Intellectual 360 points

12V output.

18V max input (limited by the 5V IC)

16V input is nominal.

2amps output current.

SOIC 8 is ideal (power pad also fine).

synchronous rectification prefered.

Soft Start I have problem finding any at all.

Good regulation.

Only IC I can find which is close is the LMR23630. If it had SS then it would be perfect overall.

0 Andy Chen over 7 years ago in reply to Chris Swinson

TI__Mastermind 33355 points

Hi

Pls try TPS54336 28V/3A synchronous buck converter in SO8 package with external soft start.

0 Chris Swinson over 7 years ago in reply to Andy Chen

Intellectual 360 points

Thanks, I was looking at the TPS54334 but did not see the 336!

Only thing I am confused about, is on page 25 , 9.2.1.3 Application Curves, efficiency at what output voltage ? It does not seem to say, and yet other datasheet quote the output voltage, normally 3.3V or 5v etc..

0 Ryan Hu (BSR-MV) over 7 years ago in reply to Chris Swinson

TI__Expert 4035 points

Hi Chris,

Sorry for the confusing, the output voltage is 3.3V, you could refer to the EVM USER's Guide for this part, SLVUAH4. thanks.

BRs,

Ryan

0 Chris Swinson over 7 years ago in reply to Ryan Hu (BSR-MV)

Intellectual 360 points

Awesome thanks!

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tps56528: Cannot start up with high output capacitor value