I am looking to build a 12-5V step down buck regulator based on the MC34063.

The regulator will power a 5V pic and lcd.

I have seen a couple of datasheets and they say nothing (at least directly) about part selection while a datasheet for a current regulator PT4115 spells out part selection very clearly.

First a question on resistors. What tolerance for the sensing resistor? Would 5% be OK?

And for the caps? The pt4115 I mentioned spells out the use of low ESR caps but the MC34063 datasheet says nothing. Would any cap of proper value do?

 

ON ti.com download it and punch in your parameters and it will give you the circuit. I didn't log in and its been awhile since I used it (it was National Semiconductor's Smart Switcher, now also owned by TI) but it used to give you a complete design with BOM, manufacturer and part numbers of the passives. Too easy.

 

I am looking to build a 12-5V step down buck regulator based on the MC34063.

The regulator will power a 5V pic and lcd.

I have seen a couple of datasheets and they say nothing (at least directly) about part selection while a datasheet for a current regulator PT4115 spells out part selection very clearly.

First a question on resistors. What tolerance for the sensing resistor? Would 5% be OK?

And for the caps? The pt4115 I mentioned spells out the use of low ESR caps but the MC34063 datasheet says nothing. Would any cap of proper value do?

1. You don't need a current sensing resistor. If you use one, 5%.
2. You can use any capacitor.
3. You may need additional filter coil if you supply a LCD.