TPS55289: how to reduce in-rush current of Vin when turn on output

Hi Dongxing,

Thanks for reaching out.

Do you mean the inductor current or the input current? 

May I know the test condition including Vin, Vout, Iout? And could you also share the waveforms of the inrush current and Vin, Vout, iL?

BRs,

Bryce

I meant input current. the Vin is 5V, Vout is 3.3V. Iout<100mA. I can only capture Vin inrush current.

Hi Dongxing,

Thanks for feedback, could you share the Vin inrush current and the schematic you tested with?

BRs,

Bryce

This is schematic. 

I have 9V to 5V converter feeding it. the current I measured are 9V current.

Hi Dongxing,

Thanks for feedback, is the current probed from the input of TPS55289? We will also test on bench to observe the input current.

BRs,

Bryce

Hi Dongxing,

I test on EVM with removing the input e-cap, and measure current from my 5V power supply. Vout is set to 3.3V. The current during startup is below. The peak current is 1A. Do you measure the current at your input side of 9V to 5V supply? If so, you may need to check this stage.

0A load:

0.1A load:

thank you for your data. 1A is still high. do you have recommendation on how to reduce that inrush?

Hi Dongxing,

The waveform I capture at 0.1A load includes soft-start and steady state. You can see that during soft-start, there's no inrush current which is higher than the current at steady state. So I think this current cannot be reduced further. 

During the TPS55289 startup, the 5Vbus voltage will have a slight drop because of the current sinking. So the previous 9V to 5V stage response to this. I think this is the current you measured. Could you please check the 9V to 5V stage as the transient response of a buck converter is usually much faster than buck-boost converter? You can try to adjust compensation to reduce the crossover frequency of the 9V to 5V converter.

Thank you.