Tool/software:
I have a PCB with two regulators - 12V in for both and 3.3V output for one and 5V output for the other. Neither is showing a voltage on Vout. Design is utilizes minimal parts as shown in Webench: CBOOT, RBOOT, SW, VCC (internal LDO output), and PG are NC. Everything else is connected. Happy to share the actual design to TI including layout in private.
I'm most interested in getting 3.3V up and running as problem is likely common to both regulators. For 3.3V reg, Rtfb (top R) = 23.2k, bottom voltage div R = 10k. Cout min cap calculated as 40uF and I've got 47uF x 4 for Cout. Cff = 47pF. Rt = 15.4k. Cin (12V) uses 10uF x 4. Vout to GND measured at 6M(eg) ohm. VLDOIN connected to VOUT through 1ohm although there's never any voltage on Vout to drive supply the LDO. Cldo is 1uF.
The reference design doesn't have the connection between Vout and VLDOIN although the datasheet always shows this as a direct connect so I used a 1ohm with the option to no-pop. At the moment the 1ohm is installed between Vout and VLDOIN. Removing the 1ohm would leave the 1uF cap attached to VLDOIN with no other connection (as shown in the Webench design).
The web bench didn't save all of my work from a while ago when I started the design - so the last design in my webench history is the 5V regulator design. However, everything is the same with exception of the passive values to adjust for the output voltage and also the resistor I added between Vout and VLDOIN.
(Webench for 5V regulator which is basis for the 5V regulator - plug in above values for 3.3V design).
I've checked that the regulator pin 1 is on the correct side. Measured Vin actually under the minimum value in Webench (11.4V). It's measuring as 11.352V (~48mV under voltage). The external power brick supplying these regulators supplies 11.993V measured and goes through a diode which is dropping the voltage to 11.4V. Bypassing the diode (shorting it) I get the full 11.99V at Vin of both regulators and still see 0V on the output. Power brick is rated at 12V 3A output. There's no droop on Vin so this is not an overcurrent on the supply rail. I haven't attached a scope yet to see the time domain response.
