NXP Semiconductors TDA8932B - Manual (Page 25)

TDA8932B_4 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 04 — 18 December 2008 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 (
µ
F)
f
-3dB
= 60 Hz f
-3dB
= 40 Hz f
-3dB
= 20 Hz
4 680 1000 2200
6 470 680 1500
8 330 470 1000
f
3dB –
1
2
π
R
L
×
Cse
×
----------------------------------- =
Fig 10. Input configuration for reducing gain
001aad762
100
k
Ω
470 nF
470 nF
audio in R3
R1
R2
G
v tot
( )
G
v cl
( )
20
R
EQ
R
EQ
R1 R2 +
( )
+
------------------------------------------ log + =