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I'm developing a motor control board (sensorless FOC). I have a question about the differential pair traces, they are very long (the longest is about 80 mm) and crosses several gate lines. How bad is this or how much does this effect the current sensing?

I read somewhere that would lead to noise coupling, the CMRR is affected and the opamp would see different stray capacitances the input but i don't know how much this impacts the current sensing. I'm also confused about what stray capacitances has to do with that.

Specs Layout: 4 Layer, 2 oz

  • Top: GND
  • L2: Gate Traces (Yellow, Width: 50 mil)
  • L3: Sense Traces (Orange, Width: 16 mil)
  • BOT: VDD

Specs Board:

  • Current: 60 A, Voltage: 50 V
  • Opamp: TLV271
  • Gate Driver: DRV8301 (Peak Gate Current: 250mA)
  • 12 Bit ADC

Board Layout: Board Layout

Schematic Current Sensing: Schematic Current Sensing

Schematic Power Stage: Schematic Power Stage

I would be excited to receive answers, best regards, Daniel

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    \$\begingroup\$ It depends entirely on what your specification is and, what your schematic implementation is. \$\endgroup\$
    – Andy aka
    Commented Dec 27, 2022 at 10:15
  • \$\begingroup\$ Hello @Andyaka, I’ve added my schematics. You're right but I don’t really know what my specs exactly should be. The bemf and current sensing is used for the algorithm to determine the rotor position. I didn’t find any information on how accurate the sensing should be or how does it affect the algorithm. I thought with a reasonably clean current sensing it should work. My last boards look similar to this and I didn’t have any problems but I’m developing a new board (it’s my hobby ) now and I’m thinking of changing the layout and bring the opamp closer to the shunt, if that brings an advantage. \$\endgroup\$
    – Daniel Müller
    Commented Dec 27, 2022 at 11:11

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