UCC14240-Q1: No Output

Here are some recommended debug steps:

1. For new designs, change UCC14240-Q1 to UCC14241-Q1. UCC14241-Q1 has some startup and noise immunity improvements that were not captured in UCC14240.
2. Please follow the PCB design guidelines detailed in section 12.5 of the UCC14241 data sheet.
   1. The bypass capacitors should be as close to the IUC pins as possible. As with any high-frequency bypass capacitor, you don't want to place vias between the bypass cap and the pin you are trying to bypass. The goal is to force the current through the pass cap as best as possible.
   2. You could try and recover your PCB layout by placing 0402 size ceramic bypass capacitors direct across the VINP-GNDP and VDD-VEE pins. The 0402 size cap can be soldered right onto the UCC14241 package/pins - you can't get any better bypass then this...until your next PCB revision.
   3. The UCC14241-Q1 has an integrated, high-frequency transformer. You would not route signals under a transformer in a traditional power converter design and so it is recommended not to route beneath the UCC14241-Q1.
3. Use RLIM configured as RDR arrangement shown in the Excel Design Calculator Tool.
   1. Your capacitor ratio is 1.81 but your output voltage ratio is 4. These should be matching as close as possible (minus any additional bias that might be applied to VDD or VEE). Are you sure you are applying the correct output capacitor ratio according to the recommended values coming from the spreadsheet?

Steve