TDA8933 Datasheet, PDF (27/47 Pages) NXP Semiconductors – Class-D audio amplifier

NXP Semiconductors
TDA8933
Class-D audio amplifier
14.4 Single-ended capacitor
The SE capacitor forms a high-pass filter with the speaker impedance. So the frequency
response will roll off with 20 dB per decade below f_−3dB (3 dB cut-off frequency).
The 3 dB cut-off frequency is equal to:
f _–3dB = ₂----_π-----_×-----_R---¹-_L----_×----_C-----_S--_E--
(7)
Where:
f_−3dB = 3 dB cut-off frequency (Hz)
R_L = load resistance (Ω)
C_SE = single-ended capacitance (F); see Figure 37.
Table 15 shows an overview of the required SE capacitor values in the case of 60 Hz,
40 Hz or 20 Hz 3 dB cut-off frequency.
Table 15. SE capacitor values
Impedance (Ω)
4
C_SE (µF)
f_−3dB = 60 Hz
680
6
470
8
330
f_−3dB = 40 Hz
1000
680
470
f_−3dB = 20 Hz
2200
1500
1000
14.5 Gain reduction
The gain of the TDA8933 is internally fixed at 30 dB for SE, and 36 dB for BTL. The gain
can be reduced by a resistive voltage divider at the input (see Figure 9).
audio in
R1
470 nF
R3
R2
470 nF
Fig 9. Input configuration for reducing gain
100
kΩ
010aaa137
When applying a resistive divider, the total voltage gain G_v(tot) can be calculated using
Equation 8 and Equation 9:
G_v(tot) = G_v(cl) + 20log -_R---_E----_Q----₊-----^R₍---_R^E----^Q₁----₊-----_R----₂----₎
(8)
Where:
G_v(tot) = total 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)
TDA8933_1
Preliminary data sheet
Rev. 01 — 15 May 2007
© NXP B.V. 2007. All rights reserved.
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