I'm designing a buck converter circuit to step down 12V to 5V in order to power an LED circuit that requires 5V at 2.5 Amperes. I need to select the input and output capacitors for this circuit.
The datasheet recommends using a 470µF electrolytic capacitor for the input and a 220µF electrolytic capacitor for the output. However, I have strict height restrictions, and these capacitors are quite tall. Additionally, I need to use surface-mount devices (SMD) since the manufacturer will be assembling the circuit for me, and I cannot use through-hole capacitors.
I would like to explore my options. Can I use ceramic capacitors, such as a combination of 10µF and 0.1µF, instead? My load does not require a stable voltage. What do you recommend?
Honestly I’m not completely sure, but with these DL1509-type bucks you normally can’t shrink the input/output caps all the way down to a few MLCCs.
Those big 470 µF / 220 µF values in the datasheet aren’t just for smoothing the load they’re there because the converter itself needs that bulk energy and a certain ESR range to stay stable at a couple of amps.
You might be able to use low-profile SMD polymer caps (or several smaller ones in parallel) to reach roughly the same total capacitance without the tall can-style electrolytics. Then add a few ceramics (10 µF + 0.1 µF) close to the pins for high-frequency stuff.
But replacing everything with only ceramics will probably give you high ripple or weird stability issues, especially at 2.5 A.
If it were my board, I’d try to keep the total µF and ESR roughly in the same ballpark as the datasheet… just in a shorter SMD form factor
Unless you are an expert in designing switching converters I suggest you stay close to the manufacturers recommendations. If you really want to stray away from what the manufacturer recommends then build a test version of the PCB with your design. Expect to have to make several versions before it works as you intend.
