SparkFun Forums

[b_w_]

Hi all,

I am drawing up some boards that needed a very small 5volt v-reg. At the moment Im planning on using the Micrel 5205. Size is the most important thing for me (SO23-5 is small!) and the only load will be a pic12f675 that will be triggering a few small mosfets so the 5205's 150mA should be enough.

1. How important is the bypass cap feature? I have a very clean source and I am not doing any thing at high freq and would rather not give up the real estate for another cap.

2. Datasheet recommends a tantalum cap or another cap with low ESR on the output with a value of 1uF or greater. I was planning on using 10uF aluminum electrolytic. This should work right?

3. Is there maybe another small vreg capable of 12v input that I should consider?

Thanks for all your continued help!
Brian

[jasonharper]

Have you considered the PIC12HV615? It has a built-in shunt regulator, the only external component needed is a resistor. (You still need a bypass capacitor for the PIC, no power supply will change that.) It's comparable in features to the 12F675, the main difference being the lack of data EEPROM.

[leon_heller]

You should follow the manufacturer's specifications; you might have stability problems, otherwise. Ordinary Al electrolytics won't have a low ESR. If it's a one-off for hobbyist use it will probably work, but I wouldn't put a design like that into production.

Leon

[NleahciM]

You can get 10uF ceramics in 0805 packages. I suspect that is small enough for you.

[Andrew02E]

I would agree with leon_heller. Most regulators themselves don't need a capacitor to function, the capacitors just smooth the input/output voltage. If you omit the capacitors, your output voltage might oscillate, get dirty, wobble, etc. This could potentially lead to intermittent operation (voltage spikes resetting the PIC, etc.).
Personally, I would not omit the capacitors unless space constraints are your number one concern (more than reliability).

[b_w_]

Yes well, I should say I was planning on bypass capacitors in the conventional sense.... in this case using a recommended 1uF cap on the input and wanting to up the output cap to a 10uF electrolytic (various reasons including size and reducing part count as this part will be used in other variants of the pcb Im designing).

The micrel 5205 is a peculiar vreg and offers a lower noise option where an additional 3rd cap can be placed on a special bypass pin. This is purely optional according to the datasheet and otherwise this pin can be tied to vin. I would ultimately rather avoid this 3rd cap but dont want to screw everything up.

I was primarily asking how optional this 3rd cap is or how much lower the noise is? Thats not answered in the datasheet and being the part is in the Sparkfun Eagle library I thought someone here might have used it before.

You know... trying to figure out how big to build the cart before I buy the horse.
-Brian

[Andrew02E]

I don't know about the 5205, but I've seen small RF circuits using similar regulators with no bypass capacitor. They were the el-cheapo kind of circuits that put cost in front of quality, but they did work. Point is, if a RF circuit worked without a bypass capacitor, I'd think a low frequency circuit should be just fine too.