AN10436 PHILIPS [NXP Semiconductors], AN10436 Datasheet - Page 26

• Manufacturer Part Number: AN10436
• Description: TDA8932B/33(B) Class-D audio amplifier
• Manufacturer: PHILIPS [NXP Semiconductors]

NXP Semiconductors
AN10436_1
Application note
3.4.1 Input impedance
3.4.2 Gain reduction
The input impedance of the TDA832B/33(B) device is equal to R
RC filter (R2, R3 and C6) is applied to reduce the sensitivity for out-of-band disturbances.
The closed loop voltage gain at 1 kHz is equal to:
The cut-off frequency of the low-pass filter is equal to:
The AC couple capacitors form a high-pass filter, with the total input impedance
(R2 + R3 + R
Example:
Substituting R2, R3 = 4.7 kΩ and the AC-couple capacitors of C5, C7 = 470 nF in
Equation 16
Substituting R2, R3 = 4.7 kΩ and C6 = 330 pF in
frequency of 56 kHz, well above 20 kHz.
The gain of the TDA8932B/33(B) is fixed internally at 30 dB for SE configuration (or 36 dB
BTL configuration). The gain can be reduced by a resistive voltage divider at the input
(see
G
f
f
–
–
Fig 24. Input transfer function
3dB h ( )
3dB l ( )
v cl
( )
Figure
=
=
20
=
log
---------------------------------------------------------------------------- -
2π
--------------------------------------------------------- -
2π
25).
results in a cut-off frequency of 6 Hz, well below 20 Hz.
i
⋅
⎛
⎝
). The cut-off frequency of the high-pass filter is equal to:
⋅
-------------------------------
R2
(
(
---------------------------------- C6
R2
R2
R2
+
+
+
+
R
R3
R3
R3
R3
Rev. 01 — 12 December 2007
i
1
0 dB
+
) R
+
+
1
R
⋅
R
R
i
⎞
⎠
i
i
i
)
⋅
⋅
⎛
⎝
C5 C7
------------------ -
C5 C7
f
3dB(l)
⋅
⋅
⎞
⎠
TDA8932B/33(B) Class-D audio amplifier
Equation 15
f
3dB(h)
010aaa012
results in a cut-off
i
= 100 kΩ. A low pass
AN10436
© NXP B.V. 2007. All rights reserved.
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