Hi,
I want to design a development board containing Xilinx Spartan-3 XC3S400. My problem is regarding the number and values of bypass capacitors that I should use for the power supplies. I use 3 power supplies: VCCINT=3D1.2V; VCCAUX=3D2.5V; VCCO=3D3.3V. I took the Spartan-3 Starter Kit Board User Guide
XAPP623 recommends for every power supply: =3DCapacitor=3D =3DValue Quantity Percentage=3D
470 =B5F to 1000 =B5F 4% 1=2E0 to 4.7 =B5F 14% 0=2E1 to 0.47 =B5F 27% 0=2E01 to 0.047 =B5F 55%Therefore...
Bypass caps for VCCINT/VCCAUX (8 pins) according to XAPP623 =3DValue range=3D =3DNo. of Caps=3D
470 =B5F to 1000 =B5F 8 pins x 4%=3D 0.32(0) 1=2E0 to 4.7 =B5F 8 pins x14%=3D 1.12(1) 0=2E1 to 0.47 =B5F 8 pins x27%=3D 2.16(2) 0=2E01 to 0.047 =B5F 8 pins x55%=3D 4.4(5)Bypass caps for VCCO (24 pins) according to XAPP623 =3DValue range=3D =3DNo. of Caps=3D
470 =B5F to 1000 =B5F 24 pins x 4%=3D 0.96(1) 1=2E0 to 4.7 =B5F 24 pins x14%=3D 3.36(3) 0=2E1 to 0.47 =B5F 24 pins x27%=3D 6.48(7) 0=2E01 to 0.047 =B5F 24 pins x55%=3D 13.2(13)_______________ But Spartan-3 Starter Kit Board uses: For VCCINT =3DNo. of Caps=3D
2 x 10uF 6 x 0.01uF 10 x 0.047uFFor VCCAUX =3DNo. of Caps=3D
1 x 10uF 16 x 0.01uFFor VCCO =3DNo. of Caps=3D
3 x 10uF 32 x 0.047uFI would like to know how the Spartan-3 Starter Kit Board got those calculations and why it didn't use the XAPP623 recommendations and which one is better for me to choose? =20 Thank you very much JJ