TPS54116-Q1: Please explain the waveform at startup.

Hello, 

Is this start-up relative to EN or relative to VIN? Can you please post the schematic? and also a scope picture showing VIN and VOUT?

Regards

Hello.

VIN is 3.6V.

Activation is by EN.

schematic

I confirmed the design at E2E.

TPS54116-Q1: Please validate my schematic design. - Power management forum - Power management - TI E2E support forums

Regards

Hello,

would you please check the SW node waveform at start-up? It seems at start-up your circuit reveals uncontrolled pulses. These uncontrolled pulses pre-bias the output capacitance before the compensation loop reacts. 

After the measurement, change the compensation network as follow:

- Replace C21666 by 1800pF

- Replace C21667 by 120pF

Regards

Hello

I understand that the reason is insufficient phase margin.

I used 2200pF because there is a problem with the availability of 1800pF.

C21666=22000pF

C21667=120pF

I changed the parts and measured.

Can I assume that this is normal operation?

Your advice cleared me up. Thank you very much.

Regards

Hello,

Yes this is a normal operation. Please close the thread if your issue is resolved and let me know for further support.

Regards

Hello,

I measured the phase margin.

41deg→64deg improvement.

After change

I thought that the rising waveform was a broken line because the Soft Start setting was bad.

Do you understand why the rising waveform becomes a broken line if there is no phase margin?

"I would appreciate it if you could tell me."

Thanks

Hello,

With low phase margin the loop responds fast to a transient event with overshoot/undershoot and few oscillation. The start-up is transient event and this is the reason the output does not follow the soft start ramp at the beginning.

I hope this answers your question. Please close the thread if your issue is resolved.

Regards