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BQ24250: Are they design guidelines when using Switching Charger and Switching Power Supply in same product

Keyur Shah
Prodigy 70 points
Part Number: BQ24250
Other Parts Discussed in Thread: TPS63805

Hi,

I will be using the TI BQ24250YFFR to charge the battery in our product and the TI TPS63805YFFR as a 3.3V Power Supply.

Both are switching power supplies and the output of BQ24250YFFR, will connect to the input of TPS63805YFFR .

Are they design guidelines for when using 2 Switching Power supplies in same design?

Are they items I should avoid in the design to prevent issues in future?

Thank You

  • 0
    TI__Guru**** 151155 points

    Hi Keyur,

    To prevent switching noise interaction, it is good practice to layout all external components close to each switching IC with wide traces for the power (high current) paths.  For the buck converter based BQ24250, the key components are the PMID, REGN and BTST caps first, then the SYS, BAT and VIN caps and finally the inductor.  For the buck=boost TPS63805, priority is the VIN and VOUT caps and then the inductor.  Make sure the GND return traces for all those caps have a short, low resistance path back to the IC GND pin.  If you use vias to another layer for any of those traces, use at least 2-3 vias in parallel.  For output voltage sense lines (FB) route them away from any switching power traces.  For those FB resistors, place the midpoint close to the IC and the GND away from switching ground (make a "separate" AGND that connects only at the IC GND pin).

    If radiated EMI is a concern, you might add an RC series snubber from the charger's SW node to ground, close to the IC SW and GND pins.  You can leave unpopulated until needed.  For EMI concerns about TPS63805, I suggest posting another e2e question about that device as I am not the expert on that device.

    Regards,

    Jeff