• Center frequency (fo)

External capacitor calculations

Figure a shows the LC75281E internal f0 control circuit. The center frequency f0 can be set to one of 11 frequencies in

1/3 octave steps by switching the resistors in the figure.

The value of the external capacitor C is determined by substituting the desired center frequency in the following formula.

fo max: Corresponds to 315 Hz in the low band row in the preceding table.

• Gain: 13 positions in 2-dB steps

• Q

No. 5913-6/10

LC75281E

Band

f1

f2

f3

f4

f5

f6

f7

f8

f9

f10

f11

External capacitor (µF)

Low

31.5

40

50

63

80

100

125

160

200

250

315

0.047

Low mid

160

200

250

315

400

500

630

800

1 k

1.25 k

1.6 k

0.0094

High mid

630

800

1 k

1.25 k

1.6 k

2 k

2.5 k

3.15 k

4 k

5 k

6.3 k

0.00235

High

1.6 k

2 k

2.5 k

3.15 k

4 k

5 k

6.3 k

8 k

10 k

12.5 k

16 k

0.0094

Cf =

1

•

Rb//Rf

2

π Rf fo max

Ra + (Rb//Rf)

Q1

Q2

Q3

Q4

Q5

Q6

Q7

Q8

Q

0.404

0.667

1.41

2.15

2.87

4.32

5.76

8.65

OCT

3

2

1

2/3

1/2

1/3

1/4

1/6

Figure a

Equivalent Circuit for Cf calculation