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BQ25601D: Is HIZ disabled automatically when an input source is plugged in?

user3611061
Prodigy 30 points
Part Number: BQ25601D
Other Parts Discussed in Thread: EV2400

Dear TI support team,

Our circuit are designing buck charger with BQ25601D.
We observed that HIZ (High impedance) mode was disabled automatically when an input source was plugged in.
However we don't know whether it is always correct behavior or not.

According to datasheet (SLUSDA2) p.18 "9.3.3.1 Power Up REGN Regulation", HIZ mode will be enabled when a poor input source is plugged in.
But we can't confirm HIZ mode will be disabled when a good one is plugged in.
Please tell us whether HIZ mode will be disabled or not.

Best regards

  • 0
    TI__Genius 11850 points

    Hi,

    With a good input source connected, HIZ mode will be disabled by default. The table below shows that at POR, HIZ mode is disabled.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Prodigy 30 points

    Dear Angelo,

    Thank you for the reply.
    Sorry, my explanation had insufficiencies.
    The above behavior is happen with a battery.
    We think that POR is not generated because there is a battery.

    Our test environment is shown as below.

    PC <---> EV2400 <---> PWR877 (BQ25601D Evaluation module) <---> Battery

    We tried the following tests. As a result, HIZ mode was disabled automatically in both tests.

    (1) Test 1 (manualy enabling HIZ mode)

    • There is no input source. But a battery is connected.
    • Set a bit 7 of REG00 (EN_HIZ) for enabling HIZ mode.
    • An input source is plugged in.
    • Then HIZ mode will be disabled automatically.

    (2) Test 2 (Shipping mode)

    • There is no input source. But a battery is connected.
    • Set a bit 3 of REG07 (BATFET_DLY) for Shipping mode.
    • Assert /QON during 2 seconds.
    • So Q4 (BATFET) turns on and HIZ mode is enabled automatically.
    • An input source is plugged in.
    • Then HIZ mode will be disabled automatically.

    Note:
    To tell the truth, we want to use Shipping mode.
    A button is connected with /QON. End-user can release Shipping mode by pressing it.
    Thus, HIZ mode will be enabled automatically. (Ref. Datasheet p.27 "9.4.4.4 /QON Pin Operations")

    Our latest circuit has a MCU (microcontroller) whose power is supplied by BQ25601D VSYS.
    MCU is booted because VSYS is rised up via releasing Shipping mode.
    We think that MCU needs to disable HIZ mode for the future charge. Therefore MCU needs to clear a bit 7 of REG00 (EN_HIZ).

    However REG00 has a configuration of IINDPM (Input Current Limit). It is configured automatically with BQ25601D.
    So we are afraid the following overwrite.

    Step 1. MCU reads 8bit value from REG00.
    Step 2. MCU clears its EN_HIZ bit.
    Step 3. BQ25601D may change IINDPM of REG00.
    Step 4. MCU writes the modified value of Step 2 into REG00. As a result, IINDPM is broken.

    If HIZ mode is disabled automatically when an input source is plugged in, MCU is not needed to write REG00 (to clear EN_HIZ).
    We want not to write REG00 if possible. So we want to make sure the behavior is always fact.

    Our latest circuit is shown as below.

    MCU <---> BQ25601D <---> Battery


    Best regards

  • 0 in reply to user3611061
    TI__Genius 11850 points

    Hi,

    The behavior you're seeing in Test 1 and Test 2 is expected. After a good input source is plugged in, the device exits HIZ mode automatically. I confirmed this on an EVM and see the same results as you.

    However, I'm not sure why the overwrite you're describing is a concern. The IINDPM register setting should not be overwritten when the MCU reads and/or writes to the EN_HIZ bit. Have you experienced this issue on your EVM?

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Prodigy 30 points

    Dear Angelo,

    Thank you. Our question is resolved by your reply.

    By the away, IINDPM is not broken in EVM. But there is its possibilty in a system of MCU and BQ25601D.
    We think about it as below.

    BQ25601D has the I2C interface. So readable/writable minimum data length is 8bit.
    REG00 includes EN_HIZ bit and IINDPM bits.
    As a result, MCU writes not only EN_HIZ bit but also IINDPM bits.

    Step 1. MCU reads 8bit value from REG00 and stores it into a variable.
                (ex. The variable has 10010111: EN_HIZ=1, IINDPM=10111.)
    Step 2. MCU clears its EN_HIZ bit.
                (ex. The variable has 00010111: EN_HIZ=0, IINDPM=10111.)
    Step 3. BQ25601D may change IINDPM of REG00 in an instant.
                (ex. REG00 has 10000100: EN_HIZ=1, IINDPM=00100)
    Step 4. MCU writes a value of the above variable into REG00. As a result, IINDPM is broken.
                (ex. REG00 has 00010111: EN_HIZ=0, IINDPM=10111)

    Now, this problem is not happen because we know writing REG00 is not needed.

    Best regards