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Hardware Errata

This page lists some issues with the hardware.

Rev 2

  • Holes for current sense resistors should be slightly larger
    • Datasheet specifies 1.5mm ±0.12mm
  • Increase spacing between heatsink and MOSFET/resistor slightly
    • Right now, the legs need to be bent at a bit of an angle, which makes fitting everything a huge pain in the ass
  • Zero offset resistor (R307, ???) is too large
    • 4M7 is too large and doesn’t let us trim out the entire DC offset (~4.5mV)
    • 1M was also too large (~3.5mV)
    • 200k works (able to trim to ~1µV remaining offset)
      • This is probably too low, maybe something like 330k or 500k is better
      • The trimming range is quite small

Rev 1

  • MOSFET gate drive voltage too low
    • VGs, with the current configuration can only drive to max +3V3. This is not sufficient to turn on the MOSFETs selected (IXTH80N075L2) with a VGs(th) of 4.5V max
    • May be salvageable by rework (op-amp powered from 5V instead) and selecting a different MOSFET
    • Future work
      • Select a MOSFET driver opamp that can be powered from ±12V
      • Update power section to generate isolated 12V (replace PS201 with PDSE1-S12-S12-S)
      • Generate 5V locally (switching supply off 12V)
  • I²C isolator (U203, ADuM1250) has the output SCL/SDA swapped
    • The I²C bus is swapped for all devices downstream of the EEPROM