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ADP5037 VOUT1 output fails to start (sometimes)

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:


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?

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