NXP Semiconductors TDA8932B - Manual (Page 22)

TDA8932B_4 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 04 — 18 December 2008 22 of 48
NXP Semiconductors
TDA8932B
Class-D audio amplifier
14. Application information
14.1 Output power estimation
The output power P
o
at THD+N = 0.5 %, just before clipping, for the SE and BTL
configuration can be estimated using Equation 2 and Equation 3 .
SE configuration:
(2)
BTL configuration:
(3)
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
)
t
w(min)
= minimum pulse width (s); 80 ns typical
f
osc
= oscillator frequency (Hz); 320 kHz typical with Rosc = 39 k
Ω
The output power P
o
at THD+N = 10 % can be estimated by:
(4)
Figure 8 and Figure 9 show the estimated output power at THD+N = 0.5 % and
THD+N = 10 % as a function of the supply voltage for SE and BTL configurations at
different load impedances. The output power is calculated with: R
DSon
= 0.15
Ω
(at
T
j
= 25
°
C), R
s
= 0.05
Ω
, R
ESR
= 0.05
Ω
and I
O(ocp)
= 4 A (minimum).
P
o 0.5%
( )
R
L
R
L
R
DSon
R
s
R
ESR
+ + +
----------------------------------------------------------  
 
1 t
w min
( )
– f
osc
Ч ( ) Ч
V
P
×
2
8 R
L
×
------------------------------------------------------------------------------------------------------------------------------------------- =
P
o 0.5%
( )
R
L
R
L
2 + R
DSon
R
s
+
( ) ×
------------------------------------------------------  
 
1 t
w min
( )
– f
osc
Ч ( ) Ч
V
P
×
2
2 R
L
×
-------------------------------------------------------------------------------------------------------------------------------------- =
P
o 10%
( ) 1.25 P
o 0.5%
( )
Ч
=