I want to make a boost converter with LTC3124, which would power a 5V device from a couple of supercaps.
1MHz switching frequency, Vout of 5V, 100mA output current
There is an example circuit for just that in it's datasheet.
![](http://i.imgur.com/ihzcmCW.png)
I rounded up some of the component values, and ended up with this:
![](http://i.imgur.com/0gQQAMe.png)
I tried to follow it's PCB guidelines, but since i can only make 2 layer boards, it's probably not perfect.
![](http://i.imgur.com/vnYvRkT.png)
![](http://i.imgur.com/7c0nSyv.jpg)
It works great for the most part. The resistor divider is somewhat moisture sensitive, but that's solvable with coating.
Problem is in how much of a "most" it is...
Once the input voltage gets above 4.4V, the thing starts whining and the chip heats up noticeably.
Considering that this is the area where it would be operating for 99.9% of time, that's not good.
The whine gets better close to 5V, and it works just fine, but it still looks and sounds wrong.
At higher currents, around 500mA it goes from being at 30*C to 70*C when the whine starts.
Now, there are two things i can think of.
First is the layout. I tied putting it on a single-sided board at first, and ended up with a roaring fiasco. This time around it works much better, but i can't really know if it's good enough.
Second is the compensation network, since i changed the component values a bit.
The pin 9, Vc, is supposed to have something called a compensation network connected to it.
There are several pages of mathematics in the datasheet on how to compute it, and i tried to follow it.
However, i can't get the numbers they are getting in the examples provided.
Probably because there are also several things i have to pick with no guidelines what-so-ever on how - the crossover frequency and the phase boost of the filter poles.
I don't think i understand the concept.
Can it be the problem, and if yes - how can i figure out how it works?