Hi,
There is an update from my side. VFB1 is actually 0.5V. I must have been probing at the wrong location.
But BUCK2 and LDO are still misbehaving.
I thought of bringing down the values of VOUT2 and VOUT3 by reducing R17 and R19. Hence I introduced 102K resistors in parallel with these resistors (R17 and R19 become 102/2 = 51K). I was expecting the output voltage to come down. But the big surprise is that VOUT2 and VOUT3 still stubbornly hold on to 3.3V!! It is the VFB2 and VFB3 which are changing to maintain VOUT constant!!! Both of them have risen to 1V.
After I removed the parallel resistor for VOUT2 (R17 brought back to 102K), the VFB2 came back to its previous level (~0.65V), with the output VOU2 still at 3.3V.
It is very strange behavior. I am expecting the VFB to be constant at 0.5V, while the output can be adjusted. But I am seeing the output constant, while VFB is changing. Just the reverse. Can someone throw some light on this.
thanks and regards,
rajesh