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TDA8932B_3 © NXP B.V. 21 June 2007. All rights reserved.
Product data sheet Rev. 03— 21 June 2007 25 of 48
NXP Semiconductors
TDA8932B
Class-D audio amplifier
The 3 dB cut-off frequency is equal to:
(7)
Where:
f
-3dB
= 3 dB cut-off frequency (Hz)
R
L
= load impedance (Ω)
Cse = single-ended capacitance (F); see Figure 36
Table 15 shows an overview of the required SE capacitor values in case of 60 Hz, 40 Hz
or 20 Hz 3 dB cut-off frequency.
14.5 Gain reduction
The gain of the TDA8932B is internally fixed at 30 dB for SE (or 36 dB for BTL). The gain
can be reduced by a resistive voltage divider at the input (see Figure 10).
When applying a resistive divider, the total closed-loop gain G
v(tot)
can be calculated by
Equation 8 and Equation 9:
(8)
Where:
G
v(tot)
= total closed-loop voltage gain (dB)
G
v(cl)
= closed-loop voltage gain, fixed at 30 dB for SE (dB)
R
EQ
= equivalent resistance, R3 and Z
i
(Ω)
R1 = series resistor (Ω)
R2 = series resistor (Ω)
Table 15. SE capacitor values
Impedance (Ω) Cse (µF)
f
-3dB
=60Hz f
-3dB
=40Hz f
-3dB
=20Hz
4 680 1000 2200
6 470 680 1500
8 330 470 1000
f
3dB–
1
2π R
L
× Cse×
-----------------------------------
=
Fig 10. Input configuration for reducing gain
001aad762
100
kΩ
470 nF
470 nF
audio in
R3
R1
R2
G
vtot()
G
vcl()
20
R
EQ
R
EQ
R1 R2+()+
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log+=