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Original question:

BQ24765 Reverse Polarity Adapter Protection

BQ24765: Reverse direction when turned off

Emmanuel Roble
Intellectual 405 points
Part Number: BQ24765

Hi, I realized that the buck charging circuit  of BQ24765 allows current being supplied from the battery being charged. It happens due to the boddy diodes on the integrated fets. When the input source is removed, the circuit is being powered by the charged battery.

  • 0
    TI__Mastermind 24075 points

    Hi Emmanuel,

       Body diode is a key component of DC/DC converter design. Closing this thread. Thanks for updating that you were able to understand/solve the original question.

  • 0 in reply to Kedar Manishankar
    Intellectual 405 points

    Sorry for not making my concern clear. What I really wanted to ask is given the natural result of body diode. How do you typically prevent the supercap load from powering the buck circuit when input supply is turned off?

  • 0 in reply to Emmanuel Roble
    TI__Mastermind 24075 points

    Hi Emmanuel,

    Buck charger needs an input voltage higher than the output voltage to be able to buck down. This charger has a V(DCIN-VFB) comparator (specified in the EC table) for reverse discharging protection. As there is the natural voltage drop across the body diode, the measured input voltage would be lower than supercap voltage and and trip this condition. With this part, an external resistor divider detects adapter voltage, and it is recommended to set this adapter detect threshold above max battery voltage, and lower than minimum adapter voltage.

       ACOK open-drain output is pulled high and charge is allowed when ACIN pin voltage is greater than 2.4V. VREF regulator and VICM current sense amplifier are active when ACIN pin voltage is greater than 0.6V, and DCINA>VDCIN_UVLO.