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Cannot start Conversion with BQ76PL536A

Ronald Johnson
Prodigy 50 points
Other Parts Discussed in Thread: BQ76PL536A

Building 4 cell pack with BQ76PL536A.  Have full SPI interface working and can write and read registers but cannot get ADC conversion cycle to run.  Getting valid status, Alert and fault values, but nothing happens when I write a 0x01 to the ADC_Convert register 0x34.  Cannot find any documentation that describes what can inhibit the conversion of if any other than the status, alerts or faults have to be clear before next conversion.  I have valid Reg50, Vref and input cell voltages.  I get 0's for the cell voltage for cell 1 with a CRC of 0x28.  Please let me know if there's something I'm missing.  I took this project over from another group that gave up.

Thanks,

Ron Johnson

  • 0
    TI__Genius 10785 points
    Things to check.

    1. Search for "Hardware Start" from the datasheet. It has details if you like.
    Make sure your CONV_H pin is connected to GND , de-asserted state(=0). .
    2. ADC Channel Selection. Default is Vcell measurement so you should have at least channel 1 measurement. This is not a root cause but something to aware of.
    3. You should be able to make measurements to cell voltage with Fault and ALERT condition but you still want to check whether it's CRC Fault or not. If it's CRC fault then it won't send proper command and won't able to measure the voltage.

    Check and Make sure CONV_H is de-asserted state(=0).
    Check this and let me know and we go from there.
  • 0
    Prodigy 50 points
    Roger,
     
    Thank you very much for your reply.  I left the conv_h pin open as the spec sheet said that it had an internal pulled down, but connecting it to Vss did the trick.  I’m now receiving consistent values for cell 2 and 3, while 0’s for cell 1 and 4.  Input pins scope good so continuing to look in to it.  This is a lot farther along than the last week.  I don’t believe there is a control register that selects each input to convert other than ADC_control (0x30) which selects the number of cells.
     
    Thanks Again,
    Ron Johnson
     
  • 0 in reply to Ronald Johnson
    TI__Genius 10785 points
    For now, wait 2mS after sending ADC conversion.

    Can you tell me the sequence of your commands?
  • 0
    Prodigy 50 points
    Roger,
     
    On initialization I’m doing the following:
     
    Broadcast Reset (0x3c),
    Address Bq76 to 1 (0x3b),
    Verify Read Address (loop back if invalid),
    Write ADC Control reg 0x30 with 0x43,
    Write Function_Config 0x40 with 0x58;
    Write IO_control 0x31 with 0x03
     
    Main loop:
     
    Read Status 0x00
    Read Alert 0x20,
    Write Alert to clear,
    Read Faults 0x21,
    Write Fault to clear,
    Write Conversion 0x34 with 0x01,
    Read cell data 0x03, 8 bytes
     
    Currently I’m single stepping all communication and displaying the Tx and Rx values on an alphanumeric display, but before I had a 2ms delay between all messages so I could see it on the display.  Still only getting 0’s and cells 1 and 4.  Verified good pin connections.  Will try reading each cell separately.
     
    Thanks,
    Ron Johnson
     
     
  • 0
    Prodigy 50 points
    Roger,
     
    It’s possible I’ve damaged this Bq76, will try replacing it.
     
    Thanks,
    Ron
     
  • 0 in reply to Ronald Johnson
    TI__Genius 10785 points
    Check Reg50, LDOA LDOD1 and LDOD2.
    Check for Power consumption.
    If they are okay then IC is probably okay.
    It's possible that you may damaged two channels but if they are okay then IC is probably okay.
  • 0 in reply to Roger Hwang
    TI__Genius 10785 points
    Do you have BQ76PL536A evm?
    Here is what I captured from bq76PL536A GUI

    SDO: 03-30-7D-30
    SDI: 00-00-00-00

    SDO: 7F-34-01-8A
    SDI: 00-00-00-00

    SDO: 03-30-3D-F7
    SDI: 00-00-00-00

    SDO: 02-00-40-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
    SDI: 00-00-00-81-1D-C3-1A-76-1A-8B-1A-7F-1A-7E-1A-8E-1A-82-27-8D-19-7F-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-3D-03-00-00-00-00-00-00-00-00-00-81-00-00-00-00-E0


    You must write 7F-3A-35-D0 (D0 is CRC) when you write to 0X40-0X4F.


    Send me the exact command to read 8 bytes...
    It should be something like.
    02 03 08 D1, D2------- D8 CRC.

    Read cell data 0x03, 8 bytes
  • 0
    Prodigy 50 points
    Roger,
     
    I’m replacing the IC now and will get these numbers when it’s back.
     
    Thanks,
    Ron