# How do I decide which which oscillation frequency and capacitors to use with a boost converter?

I'm working on a few projects where I'll be driving about 8 WS2812B LEDs on a 5V rail with an ATTiny85 (I think the whole circuit is going to draw about .5A; I'm using .75A for my calculations). I'm planning to power this with a lithium ion battery with a nominal voltage of 3.6 volts.

I need to boost the voltage to 5V. I'm considering using the XC9142B50DMR-G step-up converter to do this.

On page 11 of the datasheet (an image is included below), they have a reference implementation and specs for the other components. There seem to be two options for the oscillation frequency: 1.2MHz and 3.0MHz. I can't figure out why I'd prefer one frequency over the other.

One difference appears to be a lower supply current. What does that mean (and if it's an advantage or a disadvantage)? Are there other reasons I'd prefer one frequency to the other?

They also have 2 recommended capacitors but mouser doesn't have them in stock. Can I use any ceramic capacitors that are 10uF and at 10V and an X7T dialectric?

Here's the reference circuit and BOM specs:

• The inductor has nothing to do with the switching frequency; that's internal to the chip and I can't find anything in the datasheet about how to select it--it might be an option when you order the chip. – Hearth Jan 31 at 3:09
• @Hearth, ohhhhhhh! Thanks!! Well, I suppose my questions are still still roughly the same. I'll update the question. Thank you! – D. Patrick Jan 31 at 3:18
• @SunnyskyguyEE75 Okay, maybe "nothing to do with" was an oversimplification, but the datasheet does mention an internal oscillator used to generate the switching frequency. – Hearth Jan 31 at 14:03
• Yes f is internal and L=dt*V/dI external – Sunnyskyguy EE75 Jan 31 at 14:20

I can't figure out why I'd prefer one frequency over the other.

...

One difference appears to be a lower supply current. What does that mean (and if it's an advantage or a disadvantage)? Are there other reasons I'd prefer one frequency to the other?

Actually I cannot say anything about the "supply current vs switching frequency" thing. But the only thing I can say is "The higher the switching frequency, the smaller the power inductor". Which means that higher switching frequency helps saving more space.

High frequency PWM choices means there are good reasons for these options and one must be aware of requirements for;

-cost, of components, qty, size, performance, EM unintended interference, switching loss, temperature rise trade offs when pushing power out to the limits that constrain these.

Unless you have these requirements, it may not matter to you but L affects dI/t for a given voltage.

But as in life there are tradeoffs with size, efficiency and unintended emissions.