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TPS650250: Inductor and output capacitor selection for light load condition

Takeshi Sasaki
Expert 4480 points
Part Number: TPS650250


Hi team,

Could you give me advise how to select inductor and output capacitor at light load condition (typ 80mA, max 160mA). Below calculation results in minimum around 20uH. However, selected large 47uH causes much bigger ripple than estimated. And it seems phase compensation doesn't work (like oscillation). Lmin=[(VIN_MAX - VOUT)/(IOUT*KIND)]*VOUT/VIN_MIN*Fsw. KIND:ripple. The output capacitor is put about 10uF. 

Best regards,

Takeshi Sasaki

  • 0
    TI__Mastermind 20590 points
    Hello Sasaki-san,

    This has been assigned to the applications specialist for this device who is out today on business travel. He will provide and update early next week on this topic or when he can respond. Thank you for your patience.
  • 0
    TI__Mastermind 30310 points
    Sasaki-san,

    It sounds like this question is related to another question you asked that I just replied to: e2e.ti.com/.../2881790

    I do not have any calculations or data that I can share to help you improve light load performance while maintaining stability, but because the DC-DC converters are internally compensated you will not be able to make drastic changes from the recommended Cout and Lout values on page 5 of the TPS650250 datasheet.

    For example, if the recommended inductor is 2.2uH, then I would recommend that you use 3-5x inductance (Lo = 6-10uH) for light load, and >3x output capacitance (Co = 3x22uF) for smoothing the output further.

    To verify these assumptions, please measure frequency response and phase margin measuring the DEFDCDCx as the feedback node as outlined in my reply to your other question.