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TIDA-00901: Capacitance of bypass capacitors in the motor drive stage

John Pan
Intellectual 990 points
Part Number: TIDA-00901

Hello,

Could you please advise how the capacitance of 1 uF of C1, C2, and C3 next to each leg of the inverter of motor drive stage was determined? I am concerned whether they are too small for 20A current current. How would I know whether it is appropriate? Should I measure dv/dt across the DC link or across the MOSFET drain and source? Any ideas would be greatly appreciated.

Thanks,

John

  • 0
    TI__Expert 3830 points

    John, in addition to C1, C2 and C3, the large capacitors C8 and C9 are also in parallel from PVDD to GND node. These smooth most of the large current transients during motor operation. The smaller-value capacitors including C1-C4, C6, C10 have much less capacitance, but it is common practice to use a variety of capacitor values so that their different bands of optimal frequency response cover a wide range.

    In terms of the large (bulk) capacitors, in general bigger is better. Cost and board size will limit how much capacitance can be added. There are discussions and equations in the reference design guide that discuss capacitor selection; see section 4.6.

  • 0 in reply to Clark Kinnaird
    Intellectual 990 points

    Hi Clark,

    That is very helpful.

    Thanks,

    John