I want to use a charge pump to convert 5V to regulated 3.3V output. The charge pump I want to use has the switching frequency of 1200 kHz max. Do I need to be concerned about this switching frequency to avoid EMC issues? How is the EMI from charge pump in comparison to inductor-based regulators?
EMC = Electromagnetic Compatibility. EMI = Electromagnetic Interference.
You can try to make it compatible by using smart PCB layout techniques. But it depends on your goals and final application. New buck converters are smaller, their EMI radiation is smaller as well (EMI is proportional to line length of the components). Most of the EMI you have to worry about is from the charge/discharge in the feedback loop. So, it is very important that you get your layout optimized for reducing it all. For example,
- Large ground planes to take all that corrent away.
- Parallel traces/caps to ground or V- in order to cancel noise and EMI.
- Choosing caps to match your application.
- You can also shield your converter to prevent noise to nearby elements.
- If you have large Inductor, you might want to consider placing another one on the opposite side of the PCB to cancel the noise/EMI it can cause. You can use also Ferrite Beads to get rid of some of the EMI.
Bottom line, I guess it all matters how much noise/EMI you are willing to accept, and how much you are willing to invest in getting rid of it. As far as Inductor based switches are concered, I used both and aside of the size, I did not notice much difference. I guess in my case it all boiled down to the design.
I would guess, that - in terms of radiated emissions - a charge pump circuit will perform better than a switched inductor. But since you draw pulsed current, the conducted emissions might still be a problem. I recommend to add a filters not only to the output but also to the input.
Depending on the current you are going to consume - with the low voltage difference in mind - I would also consider using an LDO.