DC/DC Converters

Design

Input and ouput current test

It is always useful to be able to measure input and output current. As written on resistors page, it is not recommended at all to use standard 0 Ohms shunts.

My advice is to use 1206 or bigger footprint with a trace under. This gives following schematics:
 Power shunt schematics In normal case, test shunt is not populated. When current measure is required, simply cut the PCB trace and use test shunt 1206 pads.

Cut PCB here

Output L/C filter

Rule of thumb is to select a cut off frequency at 1/10 of the switching regulator frequency. L=1/{(2*pi*f)^2*C}

Multiphase DC/DC

Number of phases : Consider 20A per phase, up to 30A max

Testing

  • Load/Line regulation : Dc Vin +/- 5% (12V), check regulator voltage value at min and max load. Max and min value are determined by chips on PCBA
  • Check DC In power consumption during spinup phase and stress power consumption and in all sleep modes.
  • Power consumption : Check that power consumption of each power rail is within power budget range
  • Efficiency at 10%, 50% and 100% load (required >85% over 50% load)
  • Ripple : Check that ripple is within other PCBA components range at regulator output under maximum and minimum load
  • Dynamic load : Connect a dynamic load, change load from 30% to 100% at 1kHz frequency. Check that ripple stays in the good range
  • OCP protection level : Measure OCP protection level. Do the following tests : Power ON → Short, Short → Power On. Re power UP. Criteria, converter shall have no damage
  • Rise time (no spike)
  • Falling time < 10ms (no spike)
  • Overshoot and Undershoot : Turn On and Off each DC/DC converter. Check that over and undershoot is in other PCBA components range
  • Output voltage on product temperature range : 0°C and 40°C with product burnin
  • Check Power ON and power off sequence trough all product sleep modes / and power on
  • Cold Start : DC/DC converters starts at 0°C
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