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BQ25756: AUTONOMOUS OPERATION: are any hardware connections required to prevent reverse mode?

John Knittle
Prodigy 10 points
Part Number: BQ25756

Tool/software:

We are running the charger in standalone mode (sink only) to charge an 8S Li-Ion battery. Charging power is being supplied via USB-PD, using a TPS25751S, set to negotiate only 12V @ 5A on PPHV. We don't want to connect the I2C lines to the BQ25756. We want to understand the method to disable the reverse mode in hardware. The datasheet descriptions for pins 32 and 33, show both as VAC but with seemingly differing functions:

"Input Voltage Detection and Power – Connect a 1-μF capacitor from pin to PGND. Pin 33 is the input bias to power the IC, and ACOV/ACUV resistor divider should be connected relative to pin 33. When Reverse Mode is enabled, pin 32 is regulated to VAC_REV."

The MODE pin (17) is only described to be connected to PGND. Does this inherently block reverse operation when no I2C commands are ever received? Please clarify, Thanks!

  • +1
    TI__Expert 6315 points

    Hi John,

    In short form:

    Connect pins 32 and 33 to each other and the input voltage. Connect pin 17 to ground. When the BQ25756 is in autonomous operation, the device will not enter reverse mode.

    In long form:

    There should be no extra requirements to block reverse mode in standalone operation. The body diode of the output side high-side MOSFET should block the reverse current, and the device will not enter reverse mode without I2C.

    Pins 32 and 33 are both VAC. Do not worry about the difference between the pin 32 and pin 33. They have two different functions on the power path version of the device, but for the purpose of the BQ25756, they are the same pin and should be connected together.

    The MODE pin is from the converter only version of the device. It has no effect on the BQ25756, so we repurposed it into an additional ground connection. This pin does not have anything to do with the reverse mode.

    Let me know if this answers your question.

    Best regards,
    Michael