not boosting voltage/ regulating

kde said:

I have 15-22V in and wanted either 24/48/56VDC at ~100 watts out.

This is a boost application, so you don't need to have Q3 and Q1: replace Q1 with a jumper wire and delete Q3.

kde said:

all four fet gates show activity and appropriate levels.

What are the voltage at BG1 and TG1?

What are the switching duty cycle at BG2 and TG2?

Voltage at pin2 of L1?

Brian

BG1, TG1, BG2, TG2 were oscillating ~5v or greater, low duty cycle before change. L1 was oscillating with fet(s) change.

I replace q1 with wire, deleted q3. goes into current limit now and main IC gets hot (>50c and climbing so shut off) after a couple of seconds. Including replaced with new one, same issue.

I ohmed out all pins and they are are high resistance (>400k)as expected. 

Pin 10 (test)is grounded.

kde

ok, I need a design review.. 

It is obvious I am missing something very critical. I have verified the EPAD is grounded.

This system will not come up even in a no load/minimal load (LED only).

"C:\Users\kx9\Documents\KiCad\START4REV7\START4REV3_alternate\FAB_OUTPUT\START4REV3-SAT BLOCK.pdf"

same as inserted pix.

kde said:

BG1, TG1, BG2, TG2 were oscillating ~5v or greater, low duty cycle before change.

With input Vin 15 - 22V, then BG1 and TG1 must be 5v+Vin, not just 5v which cannot turn on Q1 which is N-FET 

Brian

kde said:

BG1, TG1, BG2, TG2 were oscillating ~5v or greater, low duty cycle before change.

With input Vin 15 - 22V, then BG1 and TG1 must be 5v+Vin, not just 5v which cannot turn on Q1 which is N-FET 

Brian