Other Parts Discussed in Thread: BQ24610
Hello!
I've been working on a BQ24650 design and trying to get it to work in a 2-layer, single-sided design. The goal is to have a flexible solar charger. In my verification testing I found significant ringing on the switching PH node. I've explored a few things to try and mitigate it (Explored a snubber, tried different power FETs). I'll include the data below for all attempts, but I'm hoping someone wants to kick around ideas for ways to get rid of the ringing, or hearing anyone's experience with ringing like this being acceptable. I checked and there is no absolute maximum pin rating that I am exceeding, so I don't think that it is a poor design.
Thanks!
First, here's the schematic:
And the layout, top and bottom:
And just bottom since it is hard to see:
And here is the ringing on the PH node. Vin is 5.9V, Vout is ~3.7V, and charge current of ~2A.
A close-up of the ringing:
I started to look at snubber values, and experimented with the techniques described in TI's whitepaper, and Rohm's whitepaper, but when I saw a 10nF cap didn't cause the ringing F to half its original value, I got concerned with the amount of power a snubber would consume. Still, I tried a 1 ohm with a 1nF snubber (expecting a 0.5W power consumption) and saw some reduction in the ringing, but I don't think it's quite worth the 1/2W power draw:
Finally, I tried replacing the existing Toshiba TPN2R304PLL1QCT-ND power FETs with BSZ025N04LSATMA1 power FETs, and found the ringing had a larger overshoot but was closer to critically damped:
As I mentioned, I'd be keen to chat about ways to get rid of it (especially if it didn't require going to a 4-layer or double-sided PCBA). And I'd also like to rap about how acceptable ringing like this is.
Thanks!
