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Altera_Forum
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16 years ago

Cyclone III, huge cap at VCCD_PLL

Hi All! Altera document "Cyclone® III Device Family Pin Connection Guidelines PCG-01003-1.0" says that 470 uF capacitor must be used at digital power of PLL (besides a lot of ceramic capacitor...
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Altera_Forum
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16 years ago

Altera directs to use this cap:

11) Decouple VCCD_PLL power island with a parallel combination of 1x470uF(low ESR Tantalum), 1x4.7uF, 5x0.1uF, 2x0.01uF, 1x0.0047uF, 1x0.0022uF.

This bulk cap is used for anti-resonance spike suppression. The spike comes from ferrite bead induction and decouple caps capacitance. This case is described in AN583, which link you gave in your post. Large 470 uF cap recommended, I think, to cover all cases. User can use cap with another value, but in this case the value should be calculated and/or modeled.

The answer is found. Thanks to all.

Best regards.