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PROBLEM: Considering the figure below, I need to select an appropriate bank of capacitors for a 3 half-bridge brushless controller, which system have this characteristics:

  • VM = 60v (maximum);
  • Max Current = 100A;
  • PWM frequency: 100khz;
  • Rds(on) typical is 1.15mOhm;
  • Rshunt = 1.0mOhm.

QUESTIONS:

1- What SMD package is recommended to use for these capacitors? (I'm considering to use 1206 or 1210)

2- For the capacitance, the higher the better?

3- For the number of capacitors, the more the better?

4- How to calculate a proper C for the capacitors?

enter image description here

LAYOUT INTENTIONS:

The bulk caps will be placed as shown below, in order to get the minimum current loop:

Top Layer:

enter image description here

3D View from Top Layer:

enter image description here

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    \$\begingroup\$ Package doesn't matter that much unless you plan on soldering it by hand, in which case definitely avoid anything smaller than 0603 and probably avoid some larger ones too, depending on your soldering skill. \$\endgroup\$
    – Hearth
    Commented Feb 25, 2021 at 16:36
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    \$\begingroup\$ ESL goes down in parallel too, to a first approximation. \$\endgroup\$
    – Hearth
    Commented Feb 25, 2021 at 16:47
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    \$\begingroup\$ Oh, it's also worth knowing there are "inverse" packages like 0612 and 1012 that have the contacts on the long side, which also reduces both ESR and ESL. \$\endgroup\$
    – Hearth
    Commented Feb 25, 2021 at 16:48
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    \$\begingroup\$ ESL will be divided by the number of capacitors in parallel, assuming they're identical. Same as with ESR. \$\endgroup\$
    – Hearth
    Commented Feb 25, 2021 at 17:06
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    \$\begingroup\$ PCB layout matters a lot also. Make sure those "bulk" caps are placed as close to the bridge as possible. epc-co.com has some good appnotes one reducing the current loop and inductance in the layout. \$\endgroup\$
    – Aaron
    Commented Feb 25, 2021 at 17:06

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