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BQ76200: TIDA-00792 Reference design questions

user
Intellectual 255 points
Part Number: BQ76200
Other Parts Discussed in Thread: TIDA-00792, , BQ78350-R1

Questions on the sheet titled FETs  from the TIDA-00792 48V battery with gauge and high side switching  reference design :

1) What does the symbol E1 denote?

2) What is the use of the diode D2, D3, D4? Doesn't the BQ76200 already have zeners inside?

Question on BQ78350-R1:

1) Does BQ78350-R1 communicate with a smart charger to stop charging? 

Thanks

  • 0
    TI__Guru* 77343 points

    Hi,

    E1 denotes a spark gap. Spark gaps are a pattern on the board that is fabricated with the board and no component is installed. Here is a link to a good video on spark gaps: https://www.youtube.com/watch?v=vfP_65gSSBU

    D2, D3, and D4 usage is described in this app note: https://www.youtube.com/watch?v=vfP_65gSSBU  http://www.ti.com/lit/an/slua794/slua794.pdf

    D4 is to reduce DSG switching loss, D3 is to protect the DSG FET gate, and D2 is for CHG FET gate protection. The app note discusses each of these in detail.

    The BQ78350-R1 does provide recommended charging voltage and current under different conditions that can be read and provided to the charger. The BQ78350-R2 firmware (available to download and program to a BQ78350-R1 device) has JEITA Charge Control. I think this may be more compatible for a smart charger to read directly.

    I hope this helps.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 255 points

    Hi Matt,

    Can you please give proper link to the app note? The link you provided points to the same video.

  • 0 in reply to user
    TI__Guru* 77343 points

    Sorry about that - I messed up when copy/pasting the link. Here is the correct link: http://www.ti.com/lit/an/slua794/slua794.pdf

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 255 points

    Hi Matt,

    What justifies the use of a spark plug when there is two diodes nearby? I don't think there will be a chance for the spark plug to activate.If it is to be present, can it be switched to a better alternative as these do not have proper ratings?

    Why do we need diode D6 when there is a already a TVS diode. The TVS diodes function as normal diodes under forward direction. Please correct me if I'm wrong and also explain why these were used in the reference design. 

    Thanks

  • 0 in reply to user
    TI__Guru* 77343 points

    Hi,

    I cannot speak for the ESD choices made on this specific board design. There are multiple options to address system level ESD and it could be that the designer for this board wanted to show multiple options. These components on this reference design appear to be copied from the BQ76200 EVM schematic - the TVS is not populated on the EVM and is there as another option for ESD protection. 

    You should design your system level ESD according to your system ESD needs. There are many approaches available, so the reference design might not be using the best optimal approach.

    Matt