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TPS2121: tps2121 inrush current

Jim Tseng
Intellectual 2250 points
Part Number: TPS2121

HI Expert,

Here is system power flow. POE 12V > TPS2121

There are many capacitor between POE and TPS2121. Around 600uF.

I want to calculate the inrush current from POE output side to TPS2121.

Where can check the TPS2121 internal MOS SOA? And how can i calculate it? please help me check am i correct or not. thanks!

I*t=C*V

I= inrush

t=POE Soft start time = 6ms

C=600uF

V=12v

Thanks Expert. 

Jim

  • +1
    TI__Mastermind 32650 points

    Hi Jim,

    We do not have an SOA curve for this device. Please note that if there is capacitor on the input side of the device, there is no slow ramp or inrush clamping capabilities that the device can perform. The TPS2121 device can only perform soft start and inrush clamping for the output load of TPS2121. 

    From your data, it looks like your inrush will be:

    I = 600uF * 12/6000us = 1.2A

    The POE needs to be able to provide 1.2A or inrush followed by the whatever downstream load you have on TPS2121 (which will be further clamped by the soft start capacitor on TPS2121)