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Original question:

BQ25756: The BQ25756 behavior with PD TPS25751

BQ25756: The Reverse mode

Alex Wang
Prodigy 140 points
Part Number: BQ25756
Other Parts Discussed in Thread: TPS25751,

Hi TI,

As the last thread indicated, we used two pairs of TPS25751 and BQ25656 with two Type-C ports as following:

When we attached some mobile phones to Type-C port, the PD TPS25751D would be Source, and we would use BQ25756's Reverse mode to deliver power from the battery
to the input(Here take CHG1_INPUT for example), then to PD's PPHV:

My question are:

1. Could we enable EN_REV of REG0x19 all the time, or only when BQ25756's CE is disabled?

2. How does BQ25756 configure its input in Reverse mode according to PD's information? For example, 

(1) Mobile 1: request 5V, 3A with PD;

(2) Mobile 2: request 20V, 3A with PD;

Take the REG0x0C for example, does BQ25756 have to configure this register to 5,000mV for (1), and 20,000mV for (2) separately?

Thanks and Regards,

Alex

  • 0
    TI__Intellectual 2630 points

    You can enable reverse any time and leave it enabled all the time. The charge does not have to be disabled to enable reverse. The system will automatically switch to reverse mode when forward mode is OFF but forward mode has priority over reverse mode.

    The VSYS_REV register will need to be configured separately for both devices as you suggfested. for 1 it will be 5000mV and for 2 it will be 20000mV.

  • 0 in reply to Utsav Gupta
    Prodigy 140 points

    Hi Utsav,

    Thanks for your response. 

    Utsav Gupta said:
    You can enable reverse any time and leave it enabled all the time.

    Do you mean the Reverse Mode would be valid all the time if I set EN_REV in the initialization phase?

    In the User Manual, the EN_REV would be reset by Adapter Plug In. So it would be set to 1 automatically when the adapter was plugged out?

    Utsav Gupta said:
    The system will automatically switch to reverse mode when forward mode is OFF

    Adapter Plug in: Forward mode is ON; Adapter Plug out: Forward mode is OFF. Right?

    Utsav Gupta said:
    The VSYS_REV register will need to be configured separately for both devices as you suggfested. for 1 it will be 5000mV and for 2 it will be 20000mV.

     OK, get it.

    Thanks and Regards,

    Alex

  • 0 in reply to Alex Wang
    TI__Intellectual 2630 points

    Sorry for the confusion. The reverse mode will indeed be reset when charging is enabled and will again have to be set once the charge is disabled.

  • 0 in reply to Utsav Gupta
    Prodigy 140 points

    Hi Utsav,

    OK. Could you kindly confirm the following question?

    Alex Wang said:
    Adapter Plug in: Forward mode is ON; Adapter Plug out: Forward mode is OFF. Right?

    And I saw there's HIZ mode, what's the purpose of this mode? Do I need to enable this mode?

    Thanks and Regards,

    Alex

  • 0 in reply to Alex Wang
    TI__Intellectual 2630 points

    When adapter is plugged in, device is in forward mode, when adapter is removed, device not charging, when reverse mode on, device in reverse mode.

    Besides the I2C host-controlled charging mode, the device also supports autonomous charging mode via resistor programmable limits. Input current, charge current and charge voltage regulation targets can be changed via the ILIM_HIZ, ICHG, and FB pins, respectively. The device can complete a charging cycle without any software intervention. Charging function is controlled via the CE pin.