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TLV1117LV: Startup waveform is not monotonic rising

TXH
Prodigy 90 points
Part Number: TLV1117LV

Hello,

I am using TLV1117LV series for my board power supply as below shown:

I found the P3V3 waveform is not monotonic rising during startup as below shown:

<CH4 is 1V2,not 2v5>

but when i use the ST LD1117 series with the same schematic and PCBA, the startup waveform is monotonic.

Pls help to figure out what needs to be changed for this LDO TLV1117LV series.  thanks a lot!

  • 0
    TI__Mastermind 36525 points

    Hello,

    The issue is very likely to be an insufficient amount of capacitance on the input.  You generally want similar or more capacitance on Vin as you have on Vout.  When the LDO turns on, it immediately transfers charge from Cin to Cout before the source supply can react.  Once the source supply reacts it will replenish charge on Cin.  So in your case there is probably a droop on Vin causing the nonmonotonic rise that you are seeing.

    Increase Cin - I would start with 100uF on the input, but you will probably need at least 3x 100uF.

    Thanks,

    - Stephen