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Original question:

BQ79616: UART Communication

BQ79616: UART Communication

Alex Trostle
Prodigy 100 points
Part Number: BQ79616

Hello,

I am trying to get UART communication working with the BQ79616 chip on custom hardware

  • 10 series Li-ion cells are connected. I used the "One PCB for all channels applications" setup (search "Cell Connections" in the datasheet)
  • There is no isolation (only using one BQ79616 as a base device). The 616 GND is connected to the FTDI ground which is the cells ground.
  • The 616 RX is pulled up to CVDD onboard through a 100k resistor. The voltage is spot on at 5V.
  • The 616 TX is pulled up to 5.24V on the host side
  • The host TX can send a wake signal to the 616 RX causing the device to wake and thus internal LDO's turn on and AVDD LED on.
  • The host TX can also put the 616 device into sleep or shutdown by pulling the 616 RX lines low for the specified amounts of time
  • LDOIN=6V, DVDD=1.8V, AVDD=5V after wake up
  • 1Mbps Baud rate
  • Multiple boards have been tested and are showing the same symptom

The BQ79616 does not respond to any commands (read or write). The 616 TX line does not make any attempt to send communications (watched on an oscilloscope) even when disconnected from the rest of the circuit. There is not a lot of circuitry on the UART lines (series resistors, pullup resistors, TVS protection diodes) and they are the same as the BQ79616EVM (besides the TVS).

The UART communication works over the UART interface on the BQ79616EVM. We can auto address, read cell voltages and configure GPIO high/low.


What should we test / debug / look for? The schematic was previously reviewed by an engineer at TI.

  • 0
    TI__Prodigy 540 points

    Hi Alex, 

    As a quick check, 

    1) Did the FTDI cable and software driver work correctly with the BQ79616 EVM? I'm just confirming that it's not a software/incorrect frame issue. 

    2) If yes, can you confirm that you can see the command on the oscilloscope on DUT RX? 

    What I would also try is see if you can still write to the device like toggling TSREF and check whether the device is correctly receiving the command or not. This is to see whether the device is not processing any communication going in or if it just has trouble outputting on TX. 

    Sincerely,

    Michelle W. 

  • 0 in reply to Michelle Williams
    Prodigy 100 points

    Hi

    1. Yes the FTDI cable and software work correctly with the BQ79616EVM.
    2. Yes we can see the command on the oscilloscope on the DUT RX at the 616 pin

    We attempted to toggle a GPIO pin (which we can successfully do on the EVM) but cannot on the DUT.


    Thank you,

    Alex T.

  • 0 in reply to Alex Trostle
    TI__Prodigy 540 points

    Last questions before I would need to review schematics:

    1) Is CVDD stable while RX is toggling? Any sign that CVDD is getting pulled low when RX is low?

    2) Was the customer OTP burned on these units that are on the PCB?

    Sincerely,

    Michelle W. 

  • 0 in reply to Michelle Williams
    Prodigy 100 points

    Hi ,

    1. Yes CVDD is stable while toggling. CVDD was not getting pulled low when RX is low.
    2. The customer OTP was not burned in the units that are on the PCB.

    However, we found the issue!! DVSS was not tied to the other grounds!

    Once resolved the board is working as intended!

    Thank you,
    Alex T.