Board

Supply

Chip

Supply

C

10 F

m

C

1 F

m

C

0.1 F(x6)

m

FerriteBead

V

CC

CDCLVP2108

www.ti.com

SCAS878C – MAY 2009 – REVISED JANUARY 2016

10 Power Supply Recommendations

10.1 Power-Supply Filtering

High-performance clock buffers are sensitive to noise on the power supply, which can dramatically increase the

additive jitter of the buffer. Thus, it is essential to reduce noise from the system power supply, especially when

jitter/phase noise is very critical to applications.

Filter capacitors are used to eliminate the low-frequency noise from the power supply, where the bypass

capacitors provide the very low impedance path for high-frequency noise and guard the power-supply system

against the induced fluctuations. These bypass capacitors also provide instantaneous current surges as required

by the device and must have low equivalent series resistance (ESR). To properly use the bypass capacitors, they

must be placed very close to the power-supply pins and laid out with short loops to minimize inductance. TI

recommends adding as many high-frequency (for example, 0.1-

μF) bypass capacitors as there are supply pins in

the package. TI recommends, but does not require, inserting a ferrite bead between the board power supply and

the chip power supply that isolates the high-frequency switching noises generated by the clock driver; these

beads prevent the switching noise from leaking into the board supply. Choose an appropriate ferrite bead with

very low DC resistance because it is imperative to provide adequate isolation between the board supply and the

chip supply, as well as to maintain a voltage at the supply pins that is greater than the minimum voltage required

for proper operation.

Figure 23 shows this recommended power-supply decoupling method.

Figure 23. Power-Supply Decoupling

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