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TPS65988: OCP trigger with negative current?

John Chou62
Intellectual 2070 points
Part Number: TPS65988
Other Parts Discussed in Thread: BQ25703

hi Team,

customer using TPS65988 with bq25703 buck-boost charger. on a power bank design.

it's observed when provide power to a system board, after handshake, the VBUS is raised to 20V. however, when system power on button is pushed and starts to drain current. it's observed that the TPS76988 will trigger OCP and trigger HW RESET, but the loading is only 1.5A while the OCP threshold is ~3A.

it's observed that the system loading can have ~-200mA reverse current with the loading.

the PDIC FW version F407.06.15

we'd like to check.

1. what are the conditions that TPS65988 will trigger OCP.

2. whats the detection time and delay time when TPS65988 turns off the voltage output

3. when TPS65988 turns off the voltage output, will it proceed with a step down manner?

4. there was a fix implemented in FW to "reduce RCP sensitivity for Samsung phone's when there is transient reverse current" what is the negative current threshold?

Please check below image. Yellow line is voltage for VBus and blue one is voltage of BQ25703.

You can see that blue line keeps 20V when yellow line is decreasing. The Max./Min. current are 1.18A/-0.21A

MCU keeps BQ25703 to output 20V but 988D seems to close it MOSs.

  • 0
    TI__Mastermind 36756 points

    Hi John,

    The TPS65988 also has reverse current protection (RCP). Based on your description, I think that the RCP can be causing the disconnect in this case as the current does not exceed the trip point. Additionally, the TPS65988 also has Under Voltage Protection (UVP) for if the voltage on VBUS drops too low below the expected value (20V in this case). 

    When any of these protection events occur, the TPS65988 will simply open the power path to protect the system. 

    The Samsung specific RCP issue was for a non-compliant phone that was back feeding VBUS with ~9V when the TPS65988 was sourcing 5V to the phone. 

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    TI__Intellectual 2070 points

    hi Eric,

    appreciate the quick response.

    as the Samsung fix was to reduce the reverse current sensitivity.

    is there an actual threshold for the RCP? and that -210mA reverse current will indeed trigger the RCP?

    customer's MCU reads from the 988 and observe OCP status, will the OCP status bit also be set by the RCP detection?

    Thanks very much

  • 0 in reply to John Chou62
    TI__Mastermind 36756 points

    Hi John,

    It is possible for RCP to trigger with 210mA of reverse current. I would suggest modifying the design a bit to get rid of the Reverse current. You can also try increasing the OCP threshold by setting the Peak Current field to 200% and by reducing the UVP trip point to its lowest setting.

    Just to confirm, the TPS65988 is acting as the Power Source in this use case, right?

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    TI__Intellectual 2070 points

    hi Eric,

    yes, the TPS65988 is in a 4 series cell  power bank, as a power source to the system board.

  • 0 in reply to John Chou62
    TI__Mastermind 36756 points

    Hi John,

    Please try adjusting the OCP/UVP settings that I suggested in my previous response.

    Thank you,
    Eric