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Philips Semiconductors
13.2 MODE pin
13.3 Output power estimation
13.4 External clock
TDA8920B_2
Product data sheet
For pop noise-free start-up an RC time-constant must be applied on the MODE pin. The
bias-current setting of the VI-converter input is directly related to the voltage on the MODE
pin. In turn the bias-current setting of the VI converters is directly related to the DC output
offset voltage. Thus a slow dV/dt on the MODE pin results in a slow dV/dt for the DC
output offset voltage, resulting in pop noise-free start-up. A time-constant of 500 ms is
sufficient to guarantee pop noise-free start-up (see also
The achievable output powers in several applications (SE and BTL) can be estimated
using the following expressions:
SE:
R
L
×
------------------- -
R
+
0.4
L
P
=
---------------------------------------------------------------------------------------- -
(
)
o 1%
Maximum current (internally limited to 8 A):
×
(
V
1 t
–
P
I
=
----------------------------------------------------- -
(
)
o peak
R
+
L
BTL:
R
L
×
------------------- -
R
+
0.8
L
P
=
-------------------------------------------------------------------------------------------- -
(
)
o 1%
Maximum current (internally limited to 8 A):
×
(
2V
1 t
–
P
I
=
---------------------------------------------------------
(
)
o peak
R
L
Variables:
R
= load impedance
L
f
= oscillator frequency
osc
t
= minimum pulse width (typically 150 ns)
min
= single-sided supply voltage (so, if supply is ±30 V symmetrical, then V
V
P
P
= output power just at clipping
o(1%)
P
= output power at THD = 10 %
o(10%)
= 1.24 × P
P
o(10%)
o(1%)
When using an external clock the following accuracy of the duty cycle of the external clock
has to be taken into account: 47.5 % < δ < 52.5 %.
Rev. 02 — 07 November 2005
×
(
×
)
V
1 t
–
f
P
min
osc
×
2
R
L
×
)
f
min
osc
0.4
×
(
×
)
2V
1 t
–
f
P
min
osc
×
2
R
L
×
)
f
min
osc
+
0.8
.
2 × 100 W class-D power amplifier
Figure
4,
2
2
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
TDA8920B
5
and 7).
(1)
(2)
(3)
(4)
= 30 V)
P
16 of 34
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