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efabless / caravel

Caravel is a standard SoC harness with on chip resources to control and read/write operations from a user-dedicated space.
https://caravel-harness.readthedocs.io/
Apache License 2.0
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If I entered 1.8V from the PCB to the 3.3V analog VDD, will it work? #490

Open Shehab-Naga opened 1 year ago

Shehab-Naga commented 1 year ago

The Caravel has 4 power domains, 2 digital with 1.8 VDD and 2 analog with 3.3 VDD. In my project, I use four separate "digital" power domains, so I will need to use the analog domains for digital circuits.

My question is to able to use the analog domains for digital circuits, Can I just enter 1.8V from the PCB to the 3.3V analog VDD? or do I need to implement LDO to transfer the 3.3 VDD to 1.8 VDD?

RTimothyEdwards commented 1 year ago

Yes, you can just connect the VDDA1 and VDDA2 to the 1.8V lines. These two power domains are unconnected on the development board by default, so you just need to wire them directly to one of the 3.3V header pins.

The VDDA1 and VDDA2 are flexible because they connect to absolutely nothing in the chip (excluding the user project) except for some ESD circuits. The ESD circuits are power clamps rated for 3.3V to 5V operation, but they will operate (presumably with a bit less ESD protection) at 1.8V supply.