Ferrite Bead

Board

Supply

VDD

Chip

Supply

C

1 µF

C

10 µF

6 xC

0.1 µF

CDCLVC1310

www.ti.com

SCAS917E – JULY 2011 – REVISED JANUARY 2014

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 or phase noise is very critical to applications.

Use of filter capacitors eliminates the low-frequency noise from power supply, where the bypass capacitors

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

induced fluctuations. The bypass capacitors also provide instantaneous current surges as required by the device,

and should have low ESR. To use the bypass capacitors properly, place them very close to the power supply

pins and lay out traces with short loops to minimize inductance. TI recommends to adding as many high-

frequency (for example, 0.1-µF) bypass capacitors as there are supply pins in the package. There is a

recommendation, but not a requirement, to insert a ferrite bead between the board power supply and the chip

power supply to isolate the high-frequency switching noises generated by the clock driver, preventing them from

leaking into the board supply. Choosing an appropriate ferrite bead with very low dc resistance is important,

because it is imperative to provide adequate isolation between the board supply and the chip supply, and to

maintain a voltage at the supply pins that is greater than the minimum voltage required for proper operation.

Figure 24. Power-Supply Decoupling

Copyright © 2011–2014, Texas Instruments Incorporated

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