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BQ76PL455A-Q1: Incorrect voltages on VM and VREF pin

Niranjan Tarle
Prodigy 100 points
Part Number: BQ76PL455A-Q1
Other Parts Discussed in Thread: BQ76PL455A,

Hi,

I have designed PCB for BQ76PL455A according to Datasheet, Design Recommendation document and BQ76PL455A EVM and GUI user guide. After soldering all components connecting 16 cells (Samsung 25R 18650 lithium-ion) the board powered up. I had the below voltages on test points

VP = 5.29V

V5VAO = 5.29V

VDIG = 5.29V

VM = 0.3V

VREF = 0.9V

BAT16 = 46V

GND = 0V  

The VM voltage ideally should be -5V whereas VREF should be 2.5V. These voltages are generated internally by the IC so there is nothing I can do. Need help getting further. Also when I try connecting the board with my laptop (USB to Serial FTDI converter), the software reports error message "could not open COM5 port".

  • 0
    TI__Genius 9301 points

    Hi Niranjan,

    You need to wake up the device (pulling wake up pin high) to be able to see 2.5V on VREF (VREF doesn't power up until the device is in idle or active state). 

    The error message could be because the device is not waking up. Can you please check your voltage level on wakeup pin?

    Regards,

    Leslie

  • 0 in reply to Leslie Marquez
    Prodigy 100 points

    Hi Leslie,

    Thank you for the suggestion. I did measure the voltage on the WAKEUP pin.

    Just after connecting the board to the laptop the WAKEUP pin receives a high to low pulse. The NPNB pin transitions from low to a high voltage level and then the board is powered. I have connected an LED to the VP pin. Before connecting the FTDI converter, the LED is OFF and after the connection, it remains turned ON. Also when I try connecting the board to my Laptop the BQ76PL455A software says "cannot open the com port" (The COM port selected is COM5 which corresponds to BQ76PL455A).

    I have also tested the board by pulling the WAKEUP pin high but the voltage level on the VREF pin is 1.45V instead of 2.5V. Need help!

    Regards,

    Niranjan

  • 0 in reply to Niranjan Tarle
    TI__Genius 9301 points

    Hi Niranjan,

    Ok. Let's start by debugging the hardware:

    • What's the voltage on VIO? 
    • Do you have any BQ76PL455A-Q1 EVMs? If so, do these power up correctly?
    • How many devices do you have stacked?
    • Please try disconnecting the FTDI cable from the board and then powering up the device and waking it up using a power supply on the wakeup pin. Then check the power pins and VREF (the pins you checked before) and see if the issue is still present. NOTE: If VIO power was previously being supplied by the FTDI cable, then you can connect it to VP to make sure it is powered up before sending the wakeup signal.

    If the device still doesn't wake up after trying to power up and wakeup from a supply, then please share your finding and your schematic for me to review it.

    Best regards,

    Leslie

  • 0 in reply to Leslie Marquez
    TI__Genius 9301 points

    Hi Niranjan,

    I will go ahead and close this thread. If you still have issues or questions please create a new post.

    Best regards,

    Leslie