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BQ79656-Q1: Proper Grounding for GPIO/Analog

Theodore Hsi
Prodigy 20 points
Part Number: BQ79656-Q1

Tool/software:

Hello,

It is very obvious that grounding is a big emphasis on the data sheet.

1)When putting in thermistors into the GPIO pins, It seems that the power comes from TSREF, which has a bypass grounded to CVSS. Since the GPIO is read by the internal ADC, is each GPIO Grounded to AVSS or CVSS. It seems that in the EVM layout that the GPIO is referenced to AVSS. If AVSS is the ground, why would TSREF be bypassed to CVSS? 

2)Since all cell readings are taken from the internal ADC, would negative side of cell1 be the AVSS reference? In other words, Figure 10-1 (P190) Would the SRN pin be connected to AVSS?

3)When tying all grounds together on L3 as shown in 12-6 (P207), is it recommended to have many stitching vias or only a few on each individual ground to minimize noise coupling?

4)When tying these grounds together is it recommended to use a Y type capacitor between the grounds? Why or Why not?

Thank you

  • 0
    TI__Prodigy 50 points

    Hi Theodore！
    You can punch more holes.
    AVSS DVSS CVSS stands for Analog, Digital, Communication VSS, all three of them are GND.
    If your BQ79656 is for a drone's 48V battery, it can be operated as designed by the EVM board, connect 3 VSS to be a GND and if your BQ79656 will acquire insulation impedance at high voltage, Y-capacitance isolation is required between high and low voltage GND, SRN connect to AVSS.

    In addition, I would like to confirm that the drones manufactured by waveareospace are military drones? 

    Best regards
    Wink Zhang

  • 0 in reply to Wink Zhang
    Prodigy 20 points

    Hello,

    Could you please clarify the specific grounding of the BQ79656? As designed by the EVM, that means that the - end of Cell1 will be the AVSS reference and the GPIO will be grounded to AVSS reference? It seems very clear in the datasheets that  these grounds are to be separated and in the EVM schematic there is the same ground symbol for all the grounds

    Yes some of our drones are military drones.