NXP Semiconductors TDA8932B - Manual (Page 24)

TDA8932B_4 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 04 — 18 December 2008 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:
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.
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
+ + +
---------------------------------------------------------- 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