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BQ79656-Q1: Stack devices

Ramchandra Bhosale
Prodigy 90 points
Part Number: BQ79656-Q1
Other Parts Discussed in Thread: BQ79616

Hi

We have system where BQ79656 is stacked with BQ79616 devices.

In our bms system, we had experienced digital resetting in BQ79656 during noisy environments.

The digital reset is happening due to under voltage on AVDD and/or DVDD.

Is there any way to prevent these digital resets as it is stopping the daisy chain communication?

How can we restore back immediately to ACTIVE MODE inspite of having digital reset?

How much delay is expected to come back to ACTIVE MODE state?

Thanks and regards

Ramchandra Bhosale

  • 0
    TI__Expert 7010 points

    Hi Ramchandra,

    What noise is causing AVDD and/or dvdd to drop under voltage? is there any additional load on AVDD or DVDD?

    AVDD and or DVDD going undervoltage should be prevented or else the digital reset will occur as its volatile memory will erased due to insufficient voltage from DVDD.

    The delay depends on how long the POR event is occurring.

    Regards,

    David

  • 0 in reply to David Ray
    Prodigy 90 points

    Hi David

    Whenever the contactors are getting turned on and off this noise is coming.

    We had tried to add 22uF cap on all the power supply lines like AVDD, DVDD, CVDD, TSREF, LDOIN and NEG5V lines.

    We have also added ESD clamping diodes.

    We have also increased RC filtering for srp and srn.

    Noise has come down but its not getting completely eliminated. 

    You can see more details in the below link

    https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1303262/bq79656-q1-noise-issue-in-bq79656-q1-stacked-with-bq79616-q1

    We are not able to eliminate the noise completely.

    We are clueless on how to run the system appropriately due to digital reset issue.

    We had also reviewed our schematic and layout. The feedback was it is correct from TI experts.

  • 0 in reply to David Ray
    Prodigy 90 points

    There is no load connected on AVDD and DVDD lines.

  • 0 in reply to Ramchandra Bhosale
    TI__Expert 7010 points

    Hi Ramchandra,

    AVDD, DVDD, and CVDD can fall due to a sudden steep increase in current.

    Is there any current increase through LDOIN seen when the high voltage contactor is connected?

    Which LDO voltage is falling first? AVDD, DVDD, CVDD, or LDOIN?

    Does this issue still appear when TSREF is turned off by the time the HV contactor is connected?

    Is there daisy chain communication occuring when the HV contactor is connected?

    Is there any additional load on CVDD? 

    Regards,

    David

  • 0 in reply to David Ray
    Prodigy 90 points

    Hi David

    We have not monitored the LDOIN current.

    Noise is appearing on all the lines simultaneously.

    There ia no additional load on CVDD.

    Yes due to digital reset the daisy chain communication is getting stopped.

    Yes even when TSREF is odf the similar issue appears.

    Thanks.

  • 0 in reply to Ramchandra Bhosale
    TI__Expert 7010 points

    Hi Ramchandra,

    It is unclear whether CVDD is falling due to the transient or if it is falling due to being turned off due to another pin. Using microsecond divisions instead of millisecond divisions, can you please capture the LDOIN and AVDD transient as well as a picture of the AVDD and CVDD transient. The millisecond division screenshots provided tell us some problem is occurring, but it is not explaining how it is occurring.

    Referring to one of the DVDD and TSREF images:

    In this picture, the HV contactor does not appear to occur when DVDD falls down. This is why we need to identify the original pin causing the issue so that the fail mode can be explained.

  • 0 in reply to David Ray
    Prodigy 90 points

    Hi David

    Please see the below waveform taken on CVDD and AVDD lines.

    Blue - Waveform of AVDD
    Yellow - Waveform of CVDD

    Thanks and regards,

    Ramchandra Bhosale

  • 0 in reply to Ramchandra Bhosale
    TI__Expert 7010 points

    Hi Ramchandra,

    I am currently discussing this issue with the FAE. With the image provided, the issue is that the large spikes are due to ripples in the GND plane's voltage. This is why the spikes can be seen on so many of the IC pins. These transients cause the voltage supplies to significantly exceed their absolute maximum ratings which will reset the IC. As the IC is not rated for such high +/- voltages, it is expected for the IC to not work due to these transients. This noise needs to be mitigated before it reaches the IC. I've directed additional questions to the FAE which are:

    1. Are there any long cables that may be introducing parasitic inductance? Inductance/inductive loads is a significant cause of HV transients.

    2.Is there any additional external filtering near the battery pack or battery pack load?

    3. Are there TVS diodes closer to the battery pack or load?

    At the end of the day, the transients on DVDD, AVDD, and CVDD will collapse the power supplies and cause the IC to reset. The cause of these transients needs to be identified and then a plan to mitigate the cause should be determined. I will continue discussing with the FAE.

    Regards,

    David