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LP5912: Rush current at startup

yoshinori.ike
Prodigy 20 points
Part Number: LP5912

I have one question.

The LP5912 is used to change a voltage from 3.8V to 1.8V.
1.8V is supplied to the external IC from the LP5912.
A maximum rush current of 1.4A flows for 20us when the external IC starts.
Is there the LP5912 at risk of being broken by 1.4A rush current for 20us?
I send the waveform of the rush current.

  • 0
    TI__Expert 6570 points

    Hi,

    1.4A exceeds the recommended operating current & short-circuit current limit. Even if current flows for a short amount of time it is possible the device is damaged. 

    BR,

    Erin

  • 0 in reply to Erin Thibeault
    Prodigy 20 points

    Diar Erin

    Thank you for answer.
    I have one additional question.

    Typical characteristics are written in the data sheet of LP5912.
    Rush current is 1.35A with typical characteristics.(Please refer to the attached file)

    Will the LP5912 break if I use it with typical characteristics like the datasheet?

  • 0 in reply to yoshinori.ike
    TI__Expert 6570 points

    Hi,

    LP5912 will not break if you use it per the recommended operating conditions provided in the datasheet. The graph you shared does show inrush current exceeding the short circuit current limit, but the inrush current is instantaneously above the short circuit current limit (1100mA). 

    I hope this is helpful,

    Erin

  • 0 in reply to Erin Thibeault
    Prodigy 20 points

    Dier　Erin-san

    Thankyou for ansower.

    I understand that if you momentarily exceed the short circuit current consumption limit (1100mA) it will break.

    I have the following understanding. Am I wrong?
    ・The waveforms（1.35A instantaneous current) in the datasheet are not the recommended conditions.
    ・The LP5912 break when the waveforms(1.35A instantaneous current) in the datasheet.

  • 0 in reply to yoshinori.ike
    TI__Expert 6570 points

    Hi Yoshinori-san,

    Apologies for the confusion. We cannot guarantee device performance outside of the recommended operating conditions. 

    In the graph from the datasheet, the output current is over 1100mA for a very short amount of time, most likely a few nanoseconds. Ideally, the current would never exceed the recommended operating conditions, but since the amount of time the current is above the 1100mA is so short, just nanoseconds, the device might be okay. 

    In your scenario, you operate at 300mA above the short circuit current limit for 20uS, because of the amount of current and the length of time, the device is at risk. I cannot guarantee the device will work outside of recommended operating conditions, but I recommend adding an input capacitor to help alleviate some of the inrush current.

    I hope this is helpful,

    Erin