Enabling the 3V3 for peripherals for a BBG cape

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kaush70
Pre-kindergarten
Pre-kindergarten
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Joined: Sat Jan 05, 2019 12:58 pm

Enabling the 3V3 for peripherals for a BBG cape

Post by kaush70 » Sat Jan 05, 2019 1:09 pm

Hi,
I am designing a custome cape for a BBG. I want to use the HDMI framer pins, which are also used for SYSBOOT. The pin status are latched on rising edge of the SYS_RESET. Based on power up sequence, the VDD_3V3B rail will be on before this. I am going to use VDD_3V3B to enable my 3V3 DC/DC switcher, which powers all my peripherals on my cape. Since there are pullup/down resistors to my 3V3 rail, these may be advertently pulled to wrong SYSBOOT values at SYSBOOT latchup.

1. Is this a likely failure mode for BBG?
2. I am planning to delay my 3V3 rail until SYS_RESET goes high to prevent this. Is it advisable?

Cheers,
Kaushalya

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