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LP5907: About inrush current

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Guru 21045 points
Part Number: LP5907

Hi Team,

 

We are evaluating LP5907UVX-4.5/NOPB on EVM.

We understand that the inrush current is one time only but the inrush current occurs two time when start up on EVM.

So, we would like to know the cause.

 

We guess that the first inrush current is caused by slight variations of VOUT.

Is this a characteristic of LP5907?

 

 

[Conditions]


 

[Result]

If CIN is increased from 1uF to 44uF, the peak of first inrush current is decreased.


 

 

Regards,

Kanemaru


  • 0
    TI__Expert 4435 points
    Hi Kanemaru-san,

    The input current is higher during the startup ramp when Vout has a larger slope. Most LDOs have variations in the output voltage ramp slope during startup resulting in variation of the input current and inrush. Inrush current generally refers to higher currents during the startup time which exceed the steady state input current.

    2 spikes of inrush current is common with an LDO that has a small ramp, brief time with near 0 slope, then continued ramp up to finish the startup. Cin is already charged in your application prior to LDO En, so more of the inrush current is provided by the larger Cin instead of from the Vin source. The inrush with larger Cin will have a smaller Iin peak, but the inrush period will be longer as shown in your scope shots.
  • 0
    Guru 140200 points
    Hi Kanemaru,

    it's not unusual to have two inrush current peaks. Many regulators do that have. After enabling the regulator the output is trying to increase the output voltage, but the output cap which is still uncharged presents a short circuit to the regulator output. So, at this moment the short circuit protection becomes active and reduces the output current nearly to zero. Directly afterwards the regulator output is ready to source current again and a new inrush current peak can be seen which is followed by a phase of nearly constant output current.

    Kai
  • 0 in reply to Eric.Preiss
    Guru 21045 points

    Hi Eric-san,

    Thank you for your prompt reply and information.

    Regards,

    Kanemaru