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Powering Circuit Q's

Hello,

I am have some questions regarding the Schematics of the BF548 ezkit (attached). Specifically

the powering sections.

Firstly, a basic questions, what is the difference between the filled square and hollow

circle schematic symbol for the power buses? The page Power Page 1, for example,

on the bottom right shows the circuitry for the VDDEXT and 3.3V, shown as filled square

and hollow circle respectively. They are both 3.3V so what is the difference?

Looking now at Power Page 2, I don't really understand the power supply for VDDDR and

5V. What does the adp1823 chip setup do? I looked briefly at its datasheet but didn't

understand how it relates to the regulation of VDDDR and 5V (again the symbols are different?).

On the bottom left of this page there are two outputs for 5V_USB? Why?

Also, on the bottom right there are these symbols (MH4, MH5, etc) but they aren't connected

to anything? What are they for?

It's pretty evident there are lots of things that I'm confused with - the power circuitry has been

a bit of a hurdle. Is there an easier design for the power supply? Would really appreciate

any reference designs that have a simpler powering system.

Thanks to anyone who can be bothered to try and help. I know it is not exactly 'fun', but it

will be much appreciated.

Cheers...

A0206-2006_CUST.pdf
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  • Hi,

    I am still confused how this circuit gets the 5V_USB to 3V. The zener voltage for D3 is 2.2V and

    the Vf of D7 is about .5V? Not sure how the 3V is derived from this?

    So basically if, if the PC provided 5V to the VBUS of the BF548 while it was is not powered it

    may cause damage. But if USBVDD is powered with 3.3V then it will not damage it?

    Also, this is a bit off on a tangent. If I want to use the VBUS to power the board, what sort of

    cap values or filtering would be required on it (other than regulation). From what I know, the USB power

    is pretty noisy?

    Thanks a lot for your help so far. It is really appreciated and has helped a lot..

    Cheers!

Reply
  • Hi,

    I am still confused how this circuit gets the 5V_USB to 3V. The zener voltage for D3 is 2.2V and

    the Vf of D7 is about .5V? Not sure how the 3V is derived from this?

    So basically if, if the PC provided 5V to the VBUS of the BF548 while it was is not powered it

    may cause damage. But if USBVDD is powered with 3.3V then it will not damage it?

    Also, this is a bit off on a tangent. If I want to use the VBUS to power the board, what sort of

    cap values or filtering would be required on it (other than regulation). From what I know, the USB power

    is pretty noisy?

    Thanks a lot for your help so far. It is really appreciated and has helped a lot..

    Cheers!

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