Voltage Drop Calculator
Calculate voltage drop across PCB traces based on geometry and current.
Formula
Acceptable Voltage Drop Guidelines
| Application | Max Drop | Notes |
|---|---|---|
| Digital Logic (3.3V) | <100 mV (3%) | Stay within spec margins |
| Sensitive Analog | <50 mV (1-2%) | Critical for ADC/DAC |
| Power Rails | <150 mV (3-5%) | Depends on regulator dropout |
| LED Circuits | <500 mV | Less critical |
| Motor/High Power | <1V | Use copper pours or bus bars |
How It Works
Every PCB trace has electrical resistance. When current flows through this resistance, it creates a voltage drop (V = I × R) and power loss (P = I² × R).
Factors Affecting Voltage Drop
- Trace Width: Wider traces have lower resistance
- Trace Length: Longer traces have higher resistance
- Copper Weight: Thicker copper has lower resistance
- Temperature: Higher temp increases resistance
- Current: Higher current means more drop
Why It Matters
- Excessive drop can cause logic errors
- Power loss creates heat
- Voltage may drop below IC minimums
- Ground bounce affects signal integrity
How to Reduce Voltage Drop
Wider Traces
Doubling trace width cuts resistance in half. Use the maximum width your layout allows for power traces.
Heavier Copper
2 oz copper has half the resistance of 1 oz. Consider 2-4 oz for power layers.
Shorter Paths
Place power components close to their sources. Minimize routing distance for power rails.
Copper Pours
Use power planes or polygon pours instead of traces for high-current paths.
Frequently Asked Questions
What's an acceptable voltage drop?
Generally, keep drop under 3-5% of your supply voltage. For 3.3V logic, that's about 100-165mV. Sensitive analog circuits may need tighter control (<1%).
Does trace width calculator account for voltage drop?
No, the trace width calculator focuses on thermal limits (current carrying capacity). A trace might be thermally adequate but have excessive voltage drop for your application. Check both.
Should I calculate drop for signal traces?
Usually not needed for digital signals (low DC current). Focus on power rails and high-current paths. For analog signals, consider ground return path resistance too.