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BQ25750: BQ25750 Switching Node Ringing Issue

Tom Tsao
Expert 1715 points
Part Number: BQ25750
Other Parts Discussed in Thread: BQ25756

Tool/software:

Hi TI team,

We are currently developing with the BQ25750 and have observed ringing on the switching node.

Here are our test conditions:

  • Switching frequency: 350 kHz

  • Buck mode: VIN = 13.6V, VBAT = 10.95V

  • Boost mode: VBAT = 10.95V to 9.6V, VSYS = 12V

Due to PCB size limitations, the inductor and the 4 power-stage MOSFETs (Q5–Q8) are placed on different layers (Top and Bottom).

We are wondering if this layer separation could be a major contributor to the ringing we are seeing.

We have tried adding a snubber circuit (R = 2.2Ω, C = 100pF), but the improvement is minimal.

Could you please provide recommendations on how to reduce the ringing (e.g., optimized snubber values, layout guidelines, or gate drive tuning)?

Any insights would be greatly appreciated. Thank you!

Best regards,

Tom

  • 0
    TI__Mastermind 29145 points

    Hello Tom,

    Have you tried add gate drive resistors to slow down the FET turn-on?

    Also, thanks for being patient with this. I'm swamped at the moment and I'll take a more in-depth look at this early next week.

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    TI__Mastermind 29145 points

    Hello Tom,

    Once again, thanks for being patient with this.

    I have a few more suggestions to improve the ringing:

    • Make sure HIDRV is routed close to SW. SW is the return path for HIDRV. Make sure both of these traces are greater than 20mils in width.

    • Make sure that LODRV isn't routed directly next to HIDRV or SW. Make sure that LODRV is routed next to GND or parallel to a GND plane.

    • You can use the gate drive strength register, REG0x3B, to reduce the gate drive strength.

    We have the BQ25756 schematic and layout guidelines here.

    We also have a FAQ for the BQ25750 power path here

    Let me know if those suggestions help. Also, let me know if you want me to review the layout of your board.

    Best Regards,
    Ethan Galloway