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BQ79600EVM: BMS with BQ79652-Q1 - No response of second stack device

Marvin Bogenschütz
Prodigy 10 points
Part Number: BQ79600EVM
Other Parts Discussed in Thread: BQ79652-Q1

Tool/software:

Hello TI-team,

I have a problem with the communication between BQ79600EVM as base device and two BQ79652-Q1 as stacks. The BQ79652-Q1s are located on the same PCB and like mentioned in the datasheet the isolation between the devices is like in Figure 10-7. 

I use the BQAutoEval 1.0.4 software to communicate with the devices.
The first problem is that Stack 2 is not always recognized.

Second problem:
When the base device just recognize the first stack the communication works for some seconds. When I restart the time of working communication decreasing every restart till I jst get a single package with the battery volatage. 
When I recognize both devices and poll the data manually I get the data of all my cells but if I change to continuous polling the communication interrupts immediately.  Then I get a COMM-Fault and a SYS-Fault
In the COMM2 register bit5 bit4 bit2 and bit0 are set and in the FAULT_SYS the DRST bit is set.

Thank you in advance.

  • 0
    TI__Intellectual 1770 points

    Hi Marvin,

    Is it possible to provide the waveforms of the signals during communication between the S1 BQ79652 COML and COMH pins? In addition, how is the BQ79600 EVM connected to the BQ79652? Just want to make sure proper isolation is held between the two devices. 

    Best Regards,

    John

  • 0 in reply to John Du
    Prodigy 10 points

    Hi John, 

    This are the waveforms which I measured between the COMLP and COMLN directly at the Pins of the Chip (red oscilloscope) and at J17 of the BQ79600EVM (blue oscilloscope). The circuit between the measurement points is shown in the pictures below, just the resistor R202 (1 kΩ) is unplaced.

    wake ping:

    request with data:

    same request with data enlarged:

    Best Regards, 
    Marvin