TPS82085 Difference of output voltage waveform of PSM mode at two case output capacitor

masahiko shimizu

Other Parts Discussed in Thread: TPS82085

Hi,

My customer is using TPS82085.
Condition is Vin=3.3V, Vout=1.2V, Iout=a few uA.

Please see below waveform.
This is same load which is above condition.
The difference is capacitor value.
Left is 22uF, Right is 44uF.

Customer uses capacitor is JMK212ABJ226MG-T.
44uF is 22uF *2.

I think this situation is PSM mode.
Switching frequency has differance at below picture.

But equation 3 in datasheet does not have element of output capacitor.

Could you let me know the reason of differance of waveform, please?

Best regards,
Shimizu

over 7 years ago

0 JohnTucker over 7 years ago

TI__Guru**** 191445 points

Moving to the modules forum...

0 masahiko shimizu over 7 years ago in reply to JohnTucker

Guru 11235 points

Hi,

How is the progress?

Best regards,

Shimizu

0 JohnTucker over 7 years ago in reply to masahiko shimizu

TI__Guru**** 191445 points

Doesn't look like anyone is looking at it. Let me see if i can find someone to help you on Monday.

0 Chris Glaser over 7 years ago

TI__Guru*** 142860 points

Hmm, I will need to think about why the equation doesn't suggest this. Is there just one SW node pulse in each case?

0 masahiko shimizu over 7 years ago in reply to Chris Glaser

Guru 11235 points

Hi Chris,

Thank you for your support.

>Is there just one SW node pulse in each case?
-> No, there is not SW node waveform. This is module product. I can not take this wavefrom.

Best regards,
Shimizu

0 Chris Glaser over 7 years ago in reply to masahiko shimizu

TI__Guru*** 142860 points

Ah, correct. You could zoom in on either Vin or Vout when Vout is rising to see about the switching. Most high frequency bursts of noise on those signals mean a SW event. Or you could probe on the inductor terminal on the device to see SW.

0 JohnTucker over 7 years ago in reply to Chris Glaser

TI__Guru**** 191445 points

Should we move this to the power modules forum?

0 Dong Shen over 7 years ago

TI__Prodigy 400 points

Hi, Shimizu

I have measured the TPS82085 EVM in lab. The test condition is Vin=3.3V, Vout=1.2V, Iout = 10uA / Iout = 27.94mA.

The result is quite different from customer's waveform, please see below.

Could you help to confirm the test condition again? Thanks.


CH3 SW CH1 VoutAC Iout=10uA Cout=22uF The waveform shape looks like customer’s, but the frequency is 125HZ.	CH3 SW CH1 VoutAC Iout=10uA Cout=44Uf The waveform shape looks like customer’s, but the frequency is 122HZ.

CH1 VoutAC CH3 SW Iout=27.94mA Cout=22uF The waveform frequency looks like customer’s, but the shape is different.	CH1 VoutAC CH3 SW Iout=27.94mA Cout=44uF The waveform frequency looks like customer’s, but the shape is different.

Best Regards

Daniel Shen

Power management

Power management forum

TPS82085 Difference of output voltage waveform of PSM mode at two case output capacitor