[Audio Cape] Why use a 1.8V regulator when expansion connector has a 1.8V rail?

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1

Why does the audio cape use a separate 1.8V LDO to power the codec when there is a 1.8V rail on the expansion connector?

2

Because there is not a 1.8V rail on the expansion header.

Gerald

3

Doesn’t the VADC (P9 Pin32) provide 1.8V? Or is that pin strictly reserved just as a reference voltage and isn’t meant to drive other circuitry?

Max

4

Yes. And it is for the ADC and not to be used for anything else. Typing stuff to the DDR power bus, like audio capes, not exactly a good idea.

Gerald

5

Got it. Thanks

Max

6

Is it only a reference, or can be used to power circuitry in the
analog front-end?

j.

7

It is intended as a reference. On the BB, the 1.8V also powered the DDR. On the BBB, it is set to 1.5/1.35V so I had to use another regulator for the 1.8V. That regulator can’t supply anywhere near the current as the BB, so on the BBB that make it even less attractive as a voltage suppy

Gerald