10 Power Supply Recommendations

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

the additive jitter of the buffer. Thus, it is essential to manage any excessive noise from the system power

supply, especially for applications where the jitter and phase noise performance is critical.

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

by the device and should have low equivalent series resistance (ESR). To properly bypass the supply, the

decoupling capacitors must be placed very close to the power-supply terminals, be connected directly to

the ground plane, 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 terminals 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 buffer; these beads prevent the

switching noise from leaking into the board supply. It is imperative to choose an appropriate ferrite bead with

very low DC resistance to provide adequate isolation between the board supply and the chip supply, as well

as to maintain a voltage at the supply terminals that is greater than the minimum voltage required for proper

operation.

Figure 10-1 shows this recommended power supply decoupling method.

GND

GND

GND

Ferrite Bead

Board

Supply

C

10 …F

C

1 …F

C

0.1 …F

Chip

Supply

V

CC

Figure 10-1. Power Supply Decoupling

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LMK1C1102, LMK1C1103, LMK1C1104

SNAS791C – DECEMBER 2019 – REVISED JUNE 2021

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