TPS628501-Q1: inrush current during startup

Hi Hirata,

The device has an internal soft start time of 1ms.

Therefore, you should be able to compute the theoretical current at startup as I = Cout*1.1V/1ms.

To give you a better idea, you can take a look at the PSpice/Simplis simulations (you find the model in the product folder TPS628501-Q1 data sheet, product information and support | TI.com).

Thanks,

Stefano

Stefano-san,

I did some simulation with PSPICE for TI.

Under my simulation, if the inductor current becomes less than 800mA, inductor current always reached to 800mA and frequency is modulated.

Question.

Q1. During the startup, if the peak inductor current does not exceed the 800mA with forced PWM mode, does this IC use PFM mode during startup irrespective of the MODE setting? and peak inductor current always reached to approx. 800mA in the PFM mode?

Q2. I see one big peak current initially which exceeds the 800mA. What is this? Does this actually happen? If so how to estimate this?

Vout = 1.1V

Load = 1Ohm

Cout = 100uF

Red wave form: Inductor current

Blue wave form: Current through load resistor

Thank you.

Regards,

Hirata

Hi Stefano-san,

Thanks for your answer.

This waveform is very helpful and your explanation makes me clear.

I appreciate your support.

Regards,

Hirata

Hi Hirata,

No problem, let us know if you need further support.

Thanks,

Stefano