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BQ25756: the charge and discharge current during constant current mode

meme wang
Prodigy 90 points
Part Number: BQ25756


BQ25756 is used as the charge and discharge chip. Is the charge and discharge current during constant current mode controlled in an open-loop manner? I couldn't find a place to set the PI parameters. Also, in reverse mode, when should discharging stop?

  • 0
    TI__Mastermind 37245 points

    Hi wang,

    I will contact you later.

  • 0 回复 Taylor
    TI__Mastermind 37245 points

    Hi wang,

    Thanks for working on this.

    meme wang 说：
    is used as the charge and discharge chip. Is the charge and discharge current during constant current mode controlled in an open-loop manner? I couldn't find a place to set the PI parameters.

     The BQ25756 is closed loop system. All compensation to the BQ25756 is internal.

    meme wang 说：
    Also, in reverse mode, when should discharging stop?

    I don't quite understand this question. Can you elaborate on this question?

  • 0 回复 Taylor
    Prodigy 90 points

    Ok, thanks a lot. Besides, I mean that, in the forward mode, the system charges the capacitor from the input power supply. During the constant current charging phase, the current is set and equal to the maximum charging current Ichg​. When the voltage reaches the set VFB​, the system transitions to constant voltage mode. Charging stops when the charging current drops to a certain value. Could you clarify which pin is used to set this certain current value?

    In the reverse mode, I would like the system to discharge the capacitor, with the discharge current also equal to Ichg. When the voltage drops to a certain value, the discharge stops. Can this functionality be achieved with BQ25756? If so, which pin is used to set this voltage value?

  • 0 回复 meme wang
    TI__Mastermind 37245 points
    meme wang 说：
    Could you clarify which pin is used to set this certain current value?
    The ICHG pin is used to set pre-charge, ICHG, and the termination current. For a capacitor, you'll want to set EN_TERM=0 and EN_PRECHG=0 to disable termination and precharge modes.
    meme wang 说：
    Can this functionality be achieved with BQ25756? If so, which pin is used to set this voltage value?
    You'll need to use I2C to program the reverse discharge current limit. You'll also need a microcontroller to monitor the capacitor voltage to stop discharging. By default, reverse discharge will stop when the capacitor voltage reaches about 2.5V or so.
    Maybe it's a system issue that we can't reply to below, so let's reply together here
    meme wang 说：
    but can the discharge current of the battery be controlled to be constant?
    Yes, the IBAT_REV register controls the discharge current.
    meme wang 说：
    Is the ICHG pin still works during the reverse mode?
    The ICHG pin does not affect reverse mode.
  • 0 回复 Taylor
    Prodigy 90 points

    Ok. thank you very much. The datasheet says when SRN is above 3 V with other conditions, the reverse mode can be allowed. Then, I though  reverse mode would be stoped when the voltage of battery decreases below 3V. During  reverse mode , the output vooltage and current can be constant by control the Vac_reg and Iac_reg, but can the discharge current of the battery be controlled to be constant? Is the ICHG pin still works during the reverse mode?