The following filtering circuits are recommended for the power supply inputs listed below.
- VAD115_VX1
- VAD18_VX1
- VAD115_FPD
- VDD33_FPD
- VAD33_USB
- VDD18_SCS
Because
the PBC layout is critical to the performance of the interfaces associated with these power
supplies, it is vital that these power supplies be treated like an analog signal.
Specifically:
- Place high-frequency components (such as ferrites and capacitors) as close to the power ball(s) as possible.
- Choose high-frequency ceramic capacitors (such as
those with a
value
of 0.1 µF, 0.01 µF, and 100 nF) that have low ESR and ESL values. Design the leads as
short as possible, and as such,
place
these capacitors
under
the package on the opposite side of the
board.
- For each power pin, a single trace (as wide as possible) must be used from the controller to the capacitor and then through the series ferrite to the power source.
- For each power pin, add a 100-nF decoupling capacitor placed near the escape
via. Add this decoupling capacitance to the capacitance recommended for filters. These are
minimum recommendations, so different layouts could require additional capacitance.
- See Table 9-1 for the recommended series ferrite component for these supplies.