1. Output Filter design
David Baba

2. Output Filter – Why? Performance Size
Reducing noise difficult to obtain single stage Buck
Would need large value of capacitance and extremely low ESR to accomplish
Effective reduction of noise spikes
Using small values of L and C filter
Reduces output ripple significantly

3. Addition of an output LC filter
Our Value Advantage
Design Rules #1
Filter Capacitor #2
Filter inductor #3
Resonance of LC filter #4
Quality Factor of LC Filter
Make First Capacitor smaller than 2nd Capacitor
Typically ceramic
Make 2nd inductor smaller than 1st inductor
Make sure Isat in greater than Iout max
Make filter resonance 3 times larger than the cross over frequency
Make sure the LC filter is damped to a Q of 1

4. Example Buck Convertor

5. Design Calculations

6. Design Calculations

7. Design Check Mathcad

8. Spice verification

9. Output Filter Noise spike reduction