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BQ21061: Reverse voltage to the LDO of BQ21061

Danilo A.
Mastermind 29970 points
Part Number: BQ21061


Hi Team,

We received this inquiry from our customer.

The LDO on this IC (BQ21061) will power the MCU and other peripherals. In order to program the MCU, I will need to supply the circuit/MCU from an external power source and therefore the LDO pin will also see this voltage.

I want to make sure that this external voltage will not damage the IC.

From the datasheet, I can't really tell with certainty that it will not since this voltage is feedback to other parts of the IC.

I need to connect an external voltage (~3V) to the OUTPUT of the LDO(LS/LDO pin) and not the input to program the MCU. The IC charger will not be powered on during this process. I want to know if this will damage or cause any issues because we don’t have access to the Vin pin on the charger IC.

Can you please confirm if this is possible without damaging the BQ21061?

Regards,

Danilo

  • 0
    TI__Mastermind 23410 points

    Hi Danilo,

    Is the BQ21061 going to be in shipmode when this occurs with the battery present? And will there be a voltage on the VINLS pin? The LDO will take input from this pin and can be controlled via registers to be enabled or disabled. I don't believe there would be a problem since the LDO pin is an output of a FET essentially but it'd be good to check on the state of the device when this programming can happen.

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    TI__Mastermind 29970 points

    Hi Anthony,

    Here is the feedback of our customer.

    Hello, most likely the IC will be in ship mode with battery attached and no voltage on VINLS, BUT there could be instances where the device is not in ship mode and the IC is powered via battery, In this case, if the LDO is configured to default output of 1.8V and a 3V is applied on the LDO output pin, will the device try to regulate the voltage and therefore sink current into itself? can you tell me if you feel this may cause any damage to the device? your help is greatly appreciated.

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Mastermind 23410 points

    Hi Danilo,

    Awesome, let me look into this today and I'll try and reply when I have a suitable answer.

    Best Regards,

    Anthony Pham

  • 0 in reply to Danilo A.
    TI__Mastermind 23410 points

    Apologies Danilo for the late reply and the second post,

    I had thought of another case and believe there is a possibility where the device could be damaged. As the FET being used from VINLS to LDO does not have back to back FET, the single body diode can conduct under the right conditions (if VLDO > VINLS). This direction of current is not intended and the allowed current isn't very high with this path and this direction. This can cause potential damage.

    Another case that may be an issue for the programming of the MCU, if the device happens to be in shipmode, the LDO 's pulldown will be enabled as in shipmode we're attempting to reduce the Iq from the battery. This may cause some issues with programming if the BQ21061 happens to be in shipmode.

    Best Regards,

    Anthony Pham