Micrel, Inc.

PL904xxx

September 11, 2015

8

Revision 1.0

tcghelp@micrel.com or (408) 955-1690

Power Supply Filtering Recommendations

Preferred filter, using Micrel’s MIC94300 or MIC94310 Ripple Blocker™:

Alternative, traditional filter, using a ferrite bead:

VDDO and VDD pins can be connected directly to the VDD power plane. For VDDA and VDDI it is recommended to use a

power supply filter as described above.

Application Information

Power Supply Decoupling

Place the smallest value decoupling capacitor (4.7nF

above) between the VDD and VSS pins, as close as

possible to those pins and on the same side of the PCB as

the IC. The shorter the physical path from VDD to the

capacitor and back from the capacitor to VSS, the more

effective the decoupling. Use one 4.7nF capacitor for each

VDD pin on the PL904xxx.

The impedance value of the ferrite bead (FB) needs to be

between 240Ω and 600Ω with a saturation current

≥150mA.

VDDO pins connect directly to the VDD plane. All VDD

pins on the PL904xxx connect to VDD after the power

supply filter.

A Ripple Blocker has advantages over using a ferrite bead.

A Ripple Blocker filters much lower frequencies than a

ferrite bead, at least two decades lower. Most ferrite beads

cause peaking in the noise filter frequency response, so

some noise frequencies are actually made worse. The

Ripple Blocker is designed to not have any noise peaking.

Output Traces

Design the traces for the output signals according to the

output logic requirements. If LVCMOS is unterminated,

add a 30Ω resistor in series with the output, as close as

possible to the output pin, and start a 50Ω trace on the

other side of the resistor.

For differential traces, you can either use a differential

design or two se

parate 50Ω traces. For EMI reasons, it is

better to use a differential design.

LVDS can be AC-coupled or DC-coupled to its termination.