4116R-R2R-503 datasheet(44/62 Pages) BOURNS

44 / 62 page

Specifications are subject to change without notice.

320

General Description

Continual advances in digital IC technology are creating

stringent demands on EMI/RFI levels in equipment.

EMI/RFI low pass filters are required in personal

computers, data terminals, test equipment and process con-

trollers for high frequency suppression into or out of elec-

tronic equipment.

Filter Selection and Design Considerations

The “roll-off” frequency fc, defined as the frequency at

which the filter passes one-half the power it receives at its

input terminal, can be specified from the low megahertz

range up to about 100MHz. This frequency, also known as

the “-3 dB” frequency, will be determined by the R and C

values chosen. Custom resistor and capacitor values are

available to optimize system performance.

The specification of these values will depend on con-

straints relating to noise frequencies, system performance

and driver loading. The following procedure is suggested to

choose appropriate values of R and C.

The first step is to determine the desired roll-off

frequency of the filter, which will lie between the signal

frequency and the dominant frequencies of the EMI/RFI

noise. By determining the pole of the filter (setting the

denominator of the transfer function equal to zero), the

roll-off frequency can be expressed in terms of R and C:

fc =

RS + RL + 2R

πC(R + RS)(R + RL)

Furthermore, the RC combination must be chosen so

that the additional RC time delay will not result in exceeding

the sampling window of the receiving IC, due to excessive

lengthening of signal rise and fall times.

Rise time from 10% to 90% of the waveform amplitude

can be calculated in terms of the circuit’s RC time constant

using the 1 –exp (–t/RC) relationship for a charging capacitor.

At 10%, t L = 0.1 time constants, and at 90%, tH = 2.3 time

constants. “Time constant” equals RthC, where Rth is the

Thevenin-equivalent resistance as seen by the capacitor.

Therefore, equating the difference in the two times to

the maximum tolerable rise (or fall) time:

tmax = t H - tL = 2.2RthC

tmax = 2.2

(R + RS)(R + RL)C

RS + RL + 2R

A final consideration is the insertion loss. As mentioned

previously, the voltage drop across the two resistors will

attenuate the voltage reaching the load. Normally, logic high

and low levels will still be within valid limits. The signal

attenuation can be minimized by choosing small R values rel-

ative to the load impedance. Typical values for R range from

10 to 50 ohms.

Bourns Low-pass Filters for EMI/RFI Suppression

NO. OF LINES

BOURNS P/N

PACKAGE

4118R-601-RC/CC

4120R-601-RC/CC

DIP

4420P-601-RC/CC

Wide Body SMD

250

Ω

500

50pF

270

Ω

101

100pF

470

Ω

181

180pF

820

Ω

201

200pF

101

100

Ω

Standard Resistance/Capacitance Values And Codes

Application Notes – EMI/RFI Filters 601 Series

4116R-R2R-503 数据表(PDF) 44 Page - Bourns Electronic Solutions

4116R-R2R-503 数据表(HTML) 44 Page - Bourns Electronic Solutions

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62

数据表下载