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Power Supplies (LDO, Buck, Boost)

Every board needs to turn its input voltage into clean rails. The two families are linear (LDO) and switching (buck/boost) β€” pick per rail, then lay each out correctly.

Choosing a regulator​

TypeEfficiencyNoiseComplexityUse when
LDO (linear)Low (drops V as heat)Very lowTinySmall drop, low current, noise-sensitive (RF, ADC, clocks)
Buck (step-down)HighSwitching rippleMediumBig drop or higher current (e.g. 12 V β†’ 3.3 V)
Boost (step-up)HighSwitching rippleMediumOutput above input (e.g. battery β†’ 5 V)

A common pattern: buck for the bulk drop, then a small LDO to clean a sensitive rail.

LDO layout​

  • Input and output capacitors right at the pins; respect the datasheet's required cap type and value (stability depends on it).
  • It dissipates (Vin βˆ’ Vout) Γ— I as heat β€” add copper pour / thermal vias for higher current.

Buck layout (the part people get wrong)​

  • Keep the hot loop (input cap β†’ high-side switch β†’ low-side switch β†’ back to cap) as small as possible β€” this loop radiates noise.
  • Input cap close to the IC; inductor close; feedback trace away from the switch node and inductor (it's sensitive).
  • Solid ground under the regulator; stitch with vias.

Protection & sequencing​

  • Reverse-polarity protection (series FET or diode) on the input.
  • Fuse / PTC and a TVS for transient/ESD on exposed inputs.
  • If rails must come up in order, plan power sequencing (enable pins, supervisors).
Heat & ripple

LDOs fail by overheating β€” always do the power-dissipation math. Bucks fail by noise β€” a big hot loop or misplaced feedback shows up as ripple and EMI.

See also​