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Original question:

TPS55288EVM-045: Power management forum

TPS55288EVM-045: TPS55288EVM-045 has too long discharging time

Eric Kung
Prodigy 30 points
Part Number: TPS55288EVM-045
Other Parts Discussed in Thread: TPS55288

Hi TI,

I've reopened the same thread where I previously discussed the issue with the TPS55288EVM having unexpectedly long discharging times (> 2min) a couple of days ago.

Despite conducting a thorough study, we are still unable to determine why the discharging time is so long.
we set the TPS55288 to enter FPWM mode when the EN pin is OFF and 06h=0x33.
As per your previous recommendation, we have measured the waveforms of SW1, SW2, and Vout during VBUS discharging, as shown below:


Could you help us to fix this issue?

Thanks.

  • 0
    TI__Mastermind 21900 points

    Hi Eric,

    As we talked before, about the DISCHA register, when Vin is still on, EN is high(can't be off) and if you set OE=0, then there will be about 100mA discharge current from Vout to GND to discharge the output voltage. The discharge function is not related to PFM or FPWM, so both 0x31 or 0x33 is ok to write to 06h.

    BRs,

    Bryce

  • 0 in reply to Bryce Xun
    Prodigy 30 points

    I made a typo earlier; I meant to write 'EN = 0' instead of 'OFF'. I am fully aware that there is a discharge current (approximately 100mA) from VOUT to GND when EN is set to 0. However, we have been struggling with this issue for quite some time. Do you have any suggestions on how to resolve this problem?
    we expect the discharging time to be shorter than 100ms when Vout from 20V to 0.5V.

  • 0 in reply to Eric Kung
    TI__Mastermind 21900 points

    Hi Eric,

    EN pin voltage can't be off or 0, I mean you need to write OE bit to 0 and keep Vin is on and EN pin voltage is high, then discharge function will work. From my calculation, with 220uF output cap, it will need about dt=C*du/i=220uF*20V/0.1A=44ms, it will not last so long if discharge function works.

    BRs,

    Bryce