EMI Bites: How Many Capacitors Do You Really Need?
When designing your circuit, one key question is:
How many capacitors are needed to meet your target impedance?
First, you need to understand your system’s target impedance, the impedance allowed for proper operation.
Once you know this target, you can calculate the number of capacitors needed using a simple formula based on your capacitor’s characteristics and the system’s transient current requirements.
Why this matters:
-Target impedance limits system noise and voltage drops.
- Capacitor series inductance affects how fast the capacitor responds.
- Transient current demands determine how much energy must be supplied quickly.
Key Insight:
The number of capacitors depends on balancing inductance, target impedance, and transient time.
Here’s a quick formula to find the capacitor count:
Number of capacitors = (2 × series inductance of chosen capacitor) ÷ (target impedance × IC transient time)
This tells you how many capacitors you need to achieve your impedance goal and support the IC’s current demands.
—Dario
P.S. Want more EMI control strategies to pass EMC?