TPS54373: Inrush Current and Sink Current at start up

Hirotsugu Kobayashi

Mastermind 9530 points

Part Number: TPS54373

Hi, team.

We evaluated TPS54373EVM.

We observed big Inrush current and Sink Current just after the starting. Please see the attached waveform.

In a simulation, we can observe the similar waveform.

I think the soft-start function isn't effective at the short period after the starting.

Is this phenomenon normal?
Why flow sink current at start up?

TPS54373_StartUp.pdf

TPS54373_startup.TSC

over 8 years ago

0 JohnTucker over 8 years ago

TI__Guru**** 191445 points

It has been a long time since I have worked with TPS54373. It has special circuitry to allow it to start into a pre-bias voltage on the output. IIRC, it compares the SS voltage to the FB voltage. It will not allow switching to occur until the SS voltage is above the fed back voltage at VSENSE. In your case, there is no pre-bias, so switching starts immediately. I think at initial start up, the device is operating at minimum controllable on time and the output voltage overshoots slightly. The control loop eventually catches up and allows the TPS54373 to sink some current to recover from the overshoot. So yes, I think this is normal operation.

0 Hirotsugu Kobayashi over 8 years ago in reply to JohnTucker

Mastermind 9530 points

Hi, John.

I attached detail waveform at initial start up.

It seems that the device is operating at Dmax in initial two pulses.

Is this phenomen the reason of the overshoot?

0 JohnTucker over 8 years ago in reply to Hirotsugu Kobayashi

TI__Guru**** 191445 points

It may be due to the input voltage dropping. It is hard to sat exactly without getting this on the bench, No one else has complained about it that I recall in the last 14 years. I am on business ravel at the moment and will not be able to dig into it further until next week.