I'm using an ADP5037 to generate 4 supply rails in a sequenced-startup configuration. Sometimes the VOUT1 converter fails to turn on as expected. It appears to be related to the ramp time on my input power--if I use a power supply with a faster ramp time (<5 ms) I seem to get reliable startup.
Here's my configuration:
AVIN=VIN1=VIN2 = 3.3V
VOUT1 set for 2.5V
VOUT2 set for 1.3V
VOUT3 set for 3.0V
VOUT4 set for 1.3V
The startup sequence is:
EN2 and EN4 (tied together) are asserted and the corresponding output voltages appear.
EN1 is asserted ~0.6ms later but VOUT1 sometimes turns on and sometimes does not.
EN3 is not asserted during power up.
Plots showing turn turn on and failed turn-on sequence are attached.
I've noticed that toggling EN1 will cause VOUT1 to start.
Any thoughts as to why VOUT1 won't turn on initially during some power-up sequences?