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NXP Semiconductors TDA8932B Uživatelský manuál Strana 24

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TDA8932B_3 © NXP B.V. 21 June 2007. All rights reserved.
Product data sheet Rev. 03— 21 June 2007 24 of 48
NXP Semiconductors
TDA8932B
Class-D audio amplifier
14.2 Output current limiting
The peak output current I
O(max)
is internally limited above a level of 4 A (minimum). During
normal operation the output current should not exceed this threshold level of 4 A
otherwise the output signal is distorted. The peak output current in SE or BTL
configurations can be estimated using Equation 5 and Equation 6.
SE configuration:
(5)
BTL configuration:
(6)
Where:
V
P
= supply voltage V
DDP1
− V
SSP1
(V) or V
DDP2
− V
SSP2
(V)
R
L
= load impedance (Ω)
R
DSon
= on-resistance power switch (Ω)
R
s
= series resistance output inductor (Ω)
R
ESR
= equivalent series resistance SE capacitor (Ω)
Example:
A4Ω speaker in the BTL configuration can be used up to a supply voltage of 18 V without
running into current limiting. Current limiting (clipping) will avoid audio holes but it causes
a comparable distortion like voltage clipping.
14.3 Speaker configuration and impedance
For a flat frequency response (second-order Butterworth filter) it is necessary to change
the low-pass filter components Llc and Clc according to the speaker configuration and
impedance. Table 14 shows the practical required values.
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).
I
O max()
0.5 V
P
×
R
L
R
DSon
R
s
R
ESR
+++
----------------------------------------------------------
4A≤≤
I
O max()
V
P
R
L
2+ R
DSon
R
s
+()×
------------------------------------------------------
4A≤≤
Table 14. Filter component values
Configuration R
L
(Ω) Llc (µH) Clc (nF)
SE 4 22 680
6 33 470
8 47 330
BTL 4 10 1500
6 15 1000
8 22 680
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