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Altera_Forum
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16 years ago

Cyclone III power for VCCA

https://www.alteraforum.com/forum/attachment.php?attachmentid=1434

https://www.alteraforum.com/forum/attachment.php?attachmentid=1435 Hi Dear all friends

hope to be fine

I am using ep3c80 device which is BGA and I designed a PCB for that and I connected VCCA pins to 2.5 v and VCCD_PLL to 1.2v, however in the pin information document from altera I find out that we sould isolate these two powers by seperate islands in the PCB design.

I did not do that and simply I connected these pins to the relative voltages and it is hard for me to change my PCB design.:(

did anybody design his/her own board with this device without isolated ilands?

I appreciate your responses

Regards

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    I think, VCCA is more critical and should be decoupled from general supply. Instead of a VCCA island, which is typically unwanted with limited power planes, individual bypass caps and ferrite beads for all four VCCA pins should be considered.

    Generally, due to the internal PLL voltage regulators, Cyclone III is considerably less susceptible to PLL supply voltage intefernces than Cyclone II. I guess, that you most likely won't have problems when connecting VCCA to common 2V5 node with good decoupling, but I didn't try and thus won't suggest it.

    In contrast, I have VCCD tied to VCCINT in all Cyclone III designs and didn't yet experience PLL lock problems. For lowest jitter, separate VCCD decoupling may be still useful.
  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    Hi Frank and Thanks for your information

    I attached my schematic here to see if I did ok with these VCCA pins or not

    actually for every VCCA pin I have two couple capacitors .1uF and 220pF. and for issolating analog power and ground I have two ferriet beads between and I have seperate ground islands.

    i am not sure that the way I used the ferriet bead for VCCA and 1.2V is ok or I need to change it

    I'm wondering if you can let me know

    thanks

    Regards