LMS75LBC176M datasheet(9/10 Pages) NSC

9 / 10 page

Application Information

POWER LINE NOISE FILTERING

A factor to consider in designing power and ground is noise

filtering. A noise filtering circuit is designed to prevent noise

generated by the integrated circuit (IC) as well as noise

entering the IC from other devices. A common filtering

method is to place by-pass capacitors (C

bp) between the

power and ground lines.

Placing a by-pass capacitor (C

bp) with the correct value at

the proper location solves many power supply noise prob-

lems. Choosing the correct capacitor value is based upon

the desired noise filtering range. Since capacitors are not

ideal, they may act more like inductors or resistors over a

specific frequency range. Thus, many times two by-pass

capacitors may be used to filter a wider bandwidth of noise.

It is highly recommended to place a larger capacitor, such as

10µF, between power supply pin and ground to filter out low

frequencies and a 0.1µF to filter out higher frequencies.

By-pass capacitors must be mounted as close as possible to

the IC to be effective. Long leads produce higher impedance

at higher frequencies due to stray inductance. Thus, this will

reduce the by-pass capacitor’s effectiveness. Surface

mounting chip capacitors are the best solution because they

have lower inductance.

20047912

FIGURE 9. Placement of by-pass Capacitors, C

LMS75LBC176M Datasheet(PDF) 9 Page - National Semiconductor (TI)