Getting a High Speed Synchronous N-Channel MOSFET Driver working right

[techn0]

Update. With the new PCBs running the NCP3420 I was getting a better high gate wave form but things were still very off. Then after Checking to see if I had damaged some mosfets I was testing around with my ohm meter when I saw something strange.
New PCB

The problem that was present on both PCBs

Trace is not connected on output of low side mosfet. I was unable to see in software and raw pcb because of the silk screen. This directly caused the boost circuit to not function making the high side gate driver useless.

Turns out it works like I expected all along with both revisions now when the trace is connected.

I am using dual 5v regulator in rev 2 which I think works better. I was using a 9v regulator for the gates for a bit but kept burning the 3420 out because it was exceeding its specs.

 

[DaveE]

Turns out it works like I expected all along with both revisions now when the trace is connected.

At the high risk of sounding like a jerk...
Let's review post #3:

My best guess is that something isn't what you think it is. A wrong or shorted trace, a backwards diode, a 220pF cap instead of 220nF, etc. I would pause and go back and systematically verify everything, especially the stuff you think is correct. This circuit should just work.

My point is this, an essential step in troubleshooting, when you think "this doesn't make sense" is to always go back a few steps and verify your assumptions, carefully this time so you don't make the same assumptions again. The more odd something is, the more likely you are thinking about it incorrectly, then it's time to put down the scope probe and think systematically.

I've lost count long ago of how often I've seen the equivalent of your story, usually in my stuff. On several occasions I've asked other EEs to come help, just as a sanity check because they think differently than me. Often troubleshooting is quick, easy, and kind of haphazard. This is usually the best first attempt. But as soon as that doesn't work, you need to switch approaches to the most slow and logically correct process you can.

On the plus side, I'm convinced the only way to learn this is to waste a lot of time and effort troubleshooting a simple, but elusive, problem. Next time you get that feeling of "what the heck, this doesn't make sense at all" you'll remember to start over with much more care. This is "the school of hard knocks", and that's a very effective school.

 

[techn0]

I couldn't agree more.. I felt like I was checking everything but much like looking for something you lost. It is always found the last place you look. Trust me I was mad at myself more then anything.

 

[Windadct]

Your application is not the same as the example in the DS. The bootstrap needs get a voltage above the Upper switch

 

[techn0]

Im with DaveE on that comment. The design is pretty much a carbon copy of the DS.