STA543SA

4 Evaluation Board

CD00061065

13/23

4.2

Evaluation Board Functional Description:

4.2.1

Input Cut-off frequency:

The input Cut-off frequency is set by the external capacitor (C4,C8,C10) values and by the

internal Input Impedance Rin ( 30K

Ω typ)

fi (cut-off) =

1 / 2

π ( Ri x Ci)

for the suggested values we have

Left/Right f i = 1 / 2

π (30KΩ x 220nF) = 24Hz

SW fi = 1 / 2

π (30KΩ x 470nF) = 11Hz

4.2.2

Output Cut-off frequency:

The output Cut-off frequency is set by the DC decoupling capacitor placed in series to the

speaker (C5,C9) value and by the Speaker Impedance

4.2.3

Crossover Network for SW:

with this board it's possible, when the Bass Audio Signal to be sent to CH.3 is not available from

the Audioprocessor, to generate it with a simple Low Pass Filter composed by an RC network.

The components to be added are R3,R6,C11:

fo = 1 / 2

π R3 (R4) x C11

example:

for R3 = R4 = 4K7

we have

C11 = 100nF

→ 340Hz

C11 = 220nF

→ 150Hz

C11 = 330nF

→ 100Hz

It is advisable at this point to modify the value of the DC decoupling capacitors in such a way to

send to L and R speakers only the high frequencies.

For example the frequency response shown in

Figure 8. was obtained with Rl = 8ohm, C5=C9=

100uF, R3=R6= 4K7 and C11=220nF

Note: In order to give the input freq response less sensitive to the spread in the Input

Impedance (Rin parameter) , it is possible to add externally two resitors R2,R7 in parallel to

Rin.

C5,C9

8ohm

6ohm

4ohm

Unit

100uF

199

265

398

Hz

220uF

90

121

181

Hz

470uF

42

56

85

Hz

1000uF

20

27

40

Hz

2200uF

9

12

18

Hz