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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 have some more questions to add to this thread.

    Bypass Caps:

    An EE note (forget which one) described how it is best to put several different decades of capacitor values as bypasses to the

    dsp to raise the natural frequency of the power supply. The bf527 ezkit uses 10,0.1 and 0.01 uF caps whereas

    the bf548 just uses 10 and 0.01. Is there a specific reason for this? From the measurements, which is the best?

    Series Terminating Resistors:

    The bf548 has series terminating resistors on the PPI and DRAM lines, but (for example) the bf527 ezkit doesn't

    have these. Again, is there a reason? Are they necessary? Obviously the less components the better but also I

    wouldn't want to compromise signal integrity.

    Max DRAM size:

    I am a bit confused about max DRAM memory size. The bf548 data sheet says each external bank supports 256MB with a

    total of 512MB. However, with 13 bit addressing and 16bit data, isn't it 2^13 * 16 = 128MB? Just wondering

    where I am going wrong.

    Power Reg:

    Again comparing the bf548 and bf527 ezkit powering. They are very different, but essentially provide the same outputs. Is the

    bf527 better to use as reference because it is newer (I think?) or is that actually more to it.

    USB:

    The USBRSET pin is meant to (from bf548 datasheet) "connect to GND through an unpopulated resistors pad" - what is the difference between this and leaving it floating? If the pad is unpopulated then isn't it floating anyway?

    Thanks in advance for any assistance with these queries.

    Cheers..

Reply
  • Hi,

    I have some more questions to add to this thread.

    Bypass Caps:

    An EE note (forget which one) described how it is best to put several different decades of capacitor values as bypasses to the

    dsp to raise the natural frequency of the power supply. The bf527 ezkit uses 10,0.1 and 0.01 uF caps whereas

    the bf548 just uses 10 and 0.01. Is there a specific reason for this? From the measurements, which is the best?

    Series Terminating Resistors:

    The bf548 has series terminating resistors on the PPI and DRAM lines, but (for example) the bf527 ezkit doesn't

    have these. Again, is there a reason? Are they necessary? Obviously the less components the better but also I

    wouldn't want to compromise signal integrity.

    Max DRAM size:

    I am a bit confused about max DRAM memory size. The bf548 data sheet says each external bank supports 256MB with a

    total of 512MB. However, with 13 bit addressing and 16bit data, isn't it 2^13 * 16 = 128MB? Just wondering

    where I am going wrong.

    Power Reg:

    Again comparing the bf548 and bf527 ezkit powering. They are very different, but essentially provide the same outputs. Is the

    bf527 better to use as reference because it is newer (I think?) or is that actually more to it.

    USB:

    The USBRSET pin is meant to (from bf548 datasheet) "connect to GND through an unpopulated resistors pad" - what is the difference between this and leaving it floating? If the pad is unpopulated then isn't it floating anyway?

    Thanks in advance for any assistance with these queries.

    Cheers..

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