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BQ25756: Can't enable reverse mode

Ao A
Prodigy 20 points
Part Number: BQ25756

Hi expert,

I am using BQ25756 for USB Power Delivery applicaiton. Recently I found that the reverse mode enable/disable is not working as expected.
Pls see below:
1.I set BQ2756 working at reverse mode and output 5V at first
2.Then set 0x19 reg = 0x00 to disable the output, the output voltage of BQ25756 starts to decrease
3.About 370ms after step2, set 0x19 reg = 0x01 to enable reverse output, but the output voltage will not inrease to 5V (The 0x0C=0x3E8 during step 1-3, which set the VAC=5V and No load in the case.). 

Any comments to this issue? Is there any time limitation to enable reverse mode after disable it?
Pls see the waveform as attached.

  • 0
    TI__Mastermind 30615 points

    Hello Ao,

    Thanks for working with us. I've got a few questions.

    What is your battery voltage during this time?

    Are you using the EVM?

    Can you get a register log/screenshot of what the registers say after step 3?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 20 points

    Hi Ethan,

    Thanks for the reply.

    I am using a battery simulator ,20V, for the test. Not the EVM but our own board. 

    The register log is difficult to get but I may find a alternate solution to avoid this issue.

    I tried to enable Hiz mode instead of setting EN_REV = 0 on step2 , and exit Hiz mode as well as setting EN_REV = 1 on step3. The output voltage now can be controlled.

    Is there any difference between EN_REV = 0 and enable Hiz mode?

    Regards 

  • 0 in reply to Ao A
    TI__Mastermind 30615 points

    Hello Ao,

    EN_REV=0 turns off reverse mode and stops the reverse/discharge switching.

    EN_HIZ=0 turns off all switching and the REGN LDO.

    Let me know if the alternative solution works for you or if you have any more questions.

    Best Regards,
    Ethan Galloway