Trace Voltage Drop

Formula

Description

Voltage drop across a PCB trace is a direct application of Ohm's law. Even small resistances become significant at high currents or when supplying low-voltage devices. For example, a 0.1Ω trace carrying 3A drops 0.3V, which is 9% of a 3.3V supply and may cause improper operation of downstream ICs. This is why power traces should be wide and short, and why sensitive circuits should have their own power connections close to the voltage regulator rather than sharing long traces with high-current loads.

Variables

• Vdrop — Voltage drop across the trace (V)
• I — Current through the trace (A)
• R — Trace resistance (Ω)

Practical Notes

Maximum acceptable voltage drop is typically 1-3% of the supply voltage for digital logic and 1% or less for analog circuits. Use copper pours and polygon fills for power distribution. Kelvin (4-wire) sensing at the load point can compensate for trace drops in precision applications. Remote voltage sensing on DC-DC converters compensates for PCB trace drops automatically.