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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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  • Hello,

    Hope this answers your questions.

    1.) There is no difference between the hollow circle and the filled in sqaure. They are both global nets that are used throught out the schematics.

    3V goes throughout the board to mulitple circuit on the board and the VDDEXT goes only to certain power pins of the BF548. JP5 and R194 allow a user to calculate the amount of current that the VDD external pins of the BF548 are consuming. The manual for the BF548 EZ-KIT elaborates more on this.

    2.) The ADP1823 is a voltage controller that helps sequence your power rails based on the enable pins. In this case 2.5V comes up and then 5V.  This circuit takes in VIN of 7.5 and is used as a dual supply. Since it is a switching circuit it brings down the 7.5V to 2.5V with little to no heat dissipation. If you need further explaination or need help is a custom power circuit design that works for your needs, we can put you in touch with a power specialist from ADI.

    In terms of the symbols the 5V, 2.5V and 3.3v are standard symbols in our schematic library. The others are just for this design. A user should treat them the same; as global power nets.

    3.) The 5V_USB connected via R280 is actually not used. There is a DNP (Do Not Populate) resistor there. It is there in case we needed to debug the circuit and needed contstant 5V applied to the USB VBUS pin.

    Currently the 5V_USB is controlled by U39 and is off when the BF548 is a device and is connecting to a USB Host (i.e. PC). Simarly, U39 is on when the BF548 is the host and is connected to a device (i.e. memory stick).

    The MH's in the schematics correspond to Mounting Holes on the board. Some are just hole, while other are connected to the ground plane. The Hole corresponding to the STAMP connectors have the Mounting holes connected to ground as this was a requirement.

Reply
  • Hello,

    Hope this answers your questions.

    1.) There is no difference between the hollow circle and the filled in sqaure. They are both global nets that are used throught out the schematics.

    3V goes throughout the board to mulitple circuit on the board and the VDDEXT goes only to certain power pins of the BF548. JP5 and R194 allow a user to calculate the amount of current that the VDD external pins of the BF548 are consuming. The manual for the BF548 EZ-KIT elaborates more on this.

    2.) The ADP1823 is a voltage controller that helps sequence your power rails based on the enable pins. In this case 2.5V comes up and then 5V.  This circuit takes in VIN of 7.5 and is used as a dual supply. Since it is a switching circuit it brings down the 7.5V to 2.5V with little to no heat dissipation. If you need further explaination or need help is a custom power circuit design that works for your needs, we can put you in touch with a power specialist from ADI.

    In terms of the symbols the 5V, 2.5V and 3.3v are standard symbols in our schematic library. The others are just for this design. A user should treat them the same; as global power nets.

    3.) The 5V_USB connected via R280 is actually not used. There is a DNP (Do Not Populate) resistor there. It is there in case we needed to debug the circuit and needed contstant 5V applied to the USB VBUS pin.

    Currently the 5V_USB is controlled by U39 and is off when the BF548 is a device and is connecting to a USB Host (i.e. PC). Simarly, U39 is on when the BF548 is the host and is connected to a device (i.e. memory stick).

    The MH's in the schematics correspond to Mounting Holes on the board. Some are just hole, while other are connected to the ground plane. The Hole corresponding to the STAMP connectors have the Mounting holes connected to ground as this was a requirement.

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