TDA8933B Datasheet, PDF (25/42 Pages) NXP Semiconductors – Class D audio amplifier

NXP Semiconductors
TDA8933B
Class D audio amplifier
14.4 Single-ended capacitor
The SE capacitor forms a high-pass filter with the speaker impedance. This means that
the frequency response will roll off with 20 dB per decade below f_−3dB and a cut-off
frequency of 3 dB.
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 (W)
• C_SE = single-ended capacitance (F); see Figure 32
Table 15 shows an overview of the required SE capacitor values in the case of a 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 TDA8933B 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
R2
R3
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)
TDA8933B_1
Preliminary data sheet
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)
Rev. 01 — 23 October 2008
© NXP B.V. 2008. All rights reserved.
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