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
and
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:
A 4
Ω
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.
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
+
+
+
----------------------------------------------------------
4 A
≤
≤
I
O max
(
)
V
P
R
L
2
+
R
DSon
R
s
+
(
)
×
------------------------------------------------------
4 A
≤
≤
Table 14.
Filter component values
Configuration
R
L
(
Ω
)
Llc (
µ
H)
Clc (nF)
SE
4
22
680
6
33
470
8
47
330
BTL
4
10
1500
6
15
1000
8
22
680
