# Is this inductor and caps a good choice for a buck converter?

I wanted to get together a simple and efficient 12V to 5V switching power regulator using only through-hole components that can be soldered to a nice protoboard. For my purposes, I need to provide 0.25A - 0.5A. Maybe 0.75A max but I doubt it. I started with the LM2675. Without making one before and only having the datasheet and google, I wanted to know if I selected proper components before I pull trigger. I will follow the manufacturers typical application schematic.

L1: 2100HT-680-V-RC - 68uH, 5.1A, 44 mOhm DCR, 5.1 Idc

Cout: RR71C680MDN1 - 68uF, 16V, 7mOhm ESR

Cin: ESY107M025AE3AA - 100uF, 25V, 130mOhm ESR

I've read a lot of recommendations to use ceramic caps for their low ESR but almost always find aluminum electrolytic caps used elsewhere. Cout was chosen for its very low ESR, but is the ESR value of Cout low enough? Are there other specifications of the capacitors I am not considering? Correct me if I'm wrong but I think the inductor should be more than good for my use. Any input would be greatly appreciated!

• Make the current loops small and provide a ground plane for voltage feedback that does not include impulsed currents. – Tony Stewart Sunnyskyguy EE75 Mar 14 '17 at 1:29
• Following up on what Tony said, bring the bottom of C1 over to GND, and bring Anode of D1 and bottom of Cout over to GND. – analogsystemsrf Mar 14 '17 at 3:33
• Please post a specific question, this is a Q&A site. See: electronics.stackexchange.com/help/dont-ask – Voltage Spike Mar 14 '17 at 4:34
• Thanks for the advice so far, would solder-bridged pads on a plated through-hole breadboard be sufficient for creating ground plane? If so should i bridge both top and bottom layers? – Sc0ttyT Mar 14 '17 at 12:42

Except for Cin it appears you are in very good shape. Your parts exceed recommendations.

These are the parts TI recommends for a LM2675 with an 11-13 Vin and 5V 750mA Output

Cb    Yageo      CC0805KRX7R9BB103
Cin   MuRata     GRM21BR61E475MA12L
Cinx  AVX        08053C104KAT2A
Cout  Panasonic  10TPE47MAZB
D1    Fairchild  MBR1020VL
L1    Bourns     SRU1048-680Y


And this is an annotated schematic with the characteristics.

750 mA

## FOR AN 500 mA

L1  Bourns  SRU1048-680Y


I can't find frequency information on the inductor, so please make sure the material has acceptable losses at chosen frequency.

I've read a lot of recommendations to use ceramic caps for their low ESR

MLCC surface mount caps' most useful feature is low inductance which makes them really good at decoupling and getting rid of switching noise.

You should add at least 1µF MLCC at input and output.

If you don't use a ground plane, then mounting inductance of your caps will be through the roof anyway, so don't bother (noise will be terrible anyway).

You don't have to use RR7 on the output, a good 100mOhm cap like EEUFR0J471 (470µF FR) will be fine, and won't resonate with the MLCC.