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TPS61022: Mode Pin

SEBA
Prodigy 110 points
Part Number: TPS61022

Hello,

when I set the mode pin to ground, the output is 5.1V when I use FPWM it's only 4.65 Volt.

Why the voltage drop in FPWM mode?

  • 0
    TI__Mastermind 34201 points

    Hi Sir,

    Could you remove the feedforward capacitor CFF1 and test again?

    If the issue still exists, please share the SW, VOUT waveform. Thank you.

  • 0 in reply to Zack Liu
    Prodigy 110 points

    Hi,

    VIN 3.2V and CFF1 removed.

    in Auto mode = 5.1V output

    in FPWM mode =  3.2V output

    Without CFF1 it drops even further  VIN = VOUT

  • 0 in reply to SEBA
    TI__Mastermind 34201 points

    Hi,

    What's the inductor saturation current level and Iout during test?

    Could you share Vin, SW, Vout waveform?

  • 0 in reply to Zack Liu
    Prodigy 110 points

    Isat = 11A

    Iout ≈ 500mA

    waveforms without CFF in AUTO mode (R39):

    VIN

    VOUT

    SW

    waveforms without CFF in FPWM mode (R38):

    VIN

    VOUT

    SW

     

  • 0 in reply to SEBA
    TI__Mastermind 34201 points

    Hi,

    That's quite strange. Is it a constant 500mA load current or pulse load current?

    What's the function of U10 HT7027? Could you supplies TPS61022 EN pin with a fixed logic high signal to make sure TPS61022 is always enabled? From your waveform in FPWM mode, it looks like when TPS61022 is enabled and switching, Vin drops so EN pin is pulled low. Then Vout decreases. 

  • 0 in reply to Zack Liu
    Prodigy 110 points

    Hi,

    I removed U10 and connect EN pin to VBAT directly, no change.

    We turn on VIN by P-Channel MOSFET.

    For further tests we fixed GATE to ground.

    On SOURCE the voltage looks fine but on DRAIN VIN drops down.

    This only happens in FPWM mode.

    We use the same circuit with other Step-Up converters without any problems.

  • 0 in reply to SEBA
    TI__Mastermind 34201 points

    Hi ,

    I think we should figure out why the input voltage has so much voltage drop.

    It looks like when TPS61022 starts switching, TPS61022 draws a lot of current from battery through the PFET, the PFET has high voltage drop so Vin decreases, then device draws even more current until it shows down. Because TPS61022 is a higher current capability device, valley switch current limit is up to 7A, so PFET voltage drop is higher. I see the PFET current capability is 4A. It may have problem when TPS61022 output power is high.

    To verify this, 1. Could you try remove or short the PFET drain to Source? Probe the inductor current or input current with current probe? 2. Use an external power supply which has enough current limit (>6A) to make sure the input voltage is stable.

    Can you answer the question: That's quite strange. Is it a constant 500mA load current or pulse load current?