1.1 volt power supply not coming up. It looks like it tries, gets to about 0.65 V and then shuts off. 3.3V is applied and the 1.2V, and 2.5 V supplies are up. The design is nearly a direct copy of the Vybrid Tower.

[markwatson]

Unfortunately, there is little information on the 1.1V LDO in the manual.  I am not sure if it is shutting down due to overcurrent or for some other reason.  I did decrease the capacitor on the LDO filter pin from 10 uF to 4.7 uF do decrease the initial surge, but that did not help.  I am wondering if a parasitic SCR is being turned on in the unit.

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[markwatson]

Jiri,

Thanks for the response.  I forgot to get back on here and mention that the problem has been resolved.  It turns out that the current limit for input power to the entire system was set too low and the 3v3 rail was collapsing briefly during power up of the processor.

Thanks,

Mark

[markwatson]

Power supply sequencing is 1.5 V first since it is used to drive the 1.2V.  When the 1.5 V is up, it signals the 3.3V to come up.  Vbat is at 3.0 V for the RTC (with a backup battery).  We have successfully used this scheme on at least three previous designs without trouble.

[jiri-b36968]

Hello Mark,

it is known issue. Main reason is power rails design. Second think is incorrect latch in Vybrid.

What is capacitance on 3V3 and 1.2V power rails and what is resistance of 3V3 power supply?

Issue can be minimized by:

- Decrease 1V2 capacitance (4u7 to 10uF)

- decrease or serial resistance of 3V3

- increase of capacitance on 3V3 voltage rail

/Jiri