AN10436 PHILIPS [NXP Semiconductors], AN10436 Datasheet - Page 27

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

NXP Semiconductors
AN10436_1
Application note
3.4.3 Reference decoupling (HVPREF)
3.5 Speaker configuration and impedance
The closed-loop voltage gain G
through the use of this equation:
Where:
Example:
Substituting R2 = R3 = 4.7 kΩ and R
a gain of G
Remark: Applying a parallel resistance to reduce the gain will affect the cut-off
frequencies of the input circuitry. It is required to compensate for this when requiring a
20 Hz to 20 kHz bandwidth.
The HVPREF voltage (equal to ½(V
HVPREF is created internally by a resistor divider (2 × 90 kΩ) located between V
V
the SE configuration. For the BTL configuration, there is a requirement only for a 100 nF
capacitor since any ripple on the HVPREF is common for both output stages.
For a flat frequency response (second order Butterworth filter), it is necessary to change
the low pass filter components L2 / L3 and C14 / C23 according to the speaker
configuration and impedance. See
Table 4
G
R
Fig 25. Resistive voltage divider at the input
SSA
EQ
v tot
R
R
R
R2, R3 = series resistors (Ω)
G
(
EQ
p
i
v(cl)
= 100 kΩ internal input resistance (Ω)
. Proper decoupling with 47 μF and 100 nF is necessary to assure a good SVRR in
=
= parallel resistor (Ω)
)
= equivalent resistance (Ω)
=
= closed-loop voltage gain 30 dB for SE and 36 dB for BTL (dB)
---------------- -
R
shows the required component values for speaker impedances of 4 Ω, 6 Ω or 8 Ω.
R
p
p
G
+
⋅
v(tot)
v cl
R
( )
R
i
i
= 26.3 dB.
+
20
log
Rev. 01 — 12 December 2007
⎛
⎝
-----------------------------------------
R
4.7 k
4.7 k
EQ
R2
R3
+
R
(
v(cl)
R2
EQ
470 nF
470 nF
C5
C7
+
Figure 35
when applying a resistive divider can be calculated
DDA
R3
P
= 22 kΩ in
)
⎞
⎠
− V
R P
22 k
SSA
for more information.
TDA8932B/33(B) Class-D audio amplifier
)) is the reference for the output. The
Equation 17
C6
330 pF
IN1P 2
IN1N 3
R i
100 k
and
010aaa013
Equation 18
AN10436
© NXP B.V. 2007. All rights reserved.
results in
DDA
27 of 55
and
(17)
(18)