AN10436 PHILIPS [NXP Semiconductors], AN10436 Datasheet - Page 32

• Manufacturer Part Number: AN10436
• Description: TDA8932B/33(B) Class-D audio amplifier
• Manufacturer: PHILIPS [NXP Semiconductors]

NXP Semiconductors
AN10436_1
Application note
3.6.1 Voltage rating
3.6.2 Lifetime
3.7 Bootstrap capacitor
Table 7
and 20 Hz.
Table 7.
The voltage rating of the SE capacitor should be at least equal to the nominal supply
voltage V
modulated heavily when the amplifier is driven at either a low frequency or during an
overload (a short circuit across the load or to V
the SE capacitor can be almost equal to the supply voltage.
The ambient temperature and the ripple current have the greatest effect on the lifetime of
the aluminium electrolytic capacitors. For lifetime considerations the SE capacitance must
be able to at least handle the ripple current that is equal to the load current at ¼ rated
output power. Only ¼ of the rated output power is taken into account, because it is not
likely that an audio amplifier is driven continuously at rated output power over a lifetime.
The ripple current at ¼ P
Where:
Example:
The ripple current of an amplifier that operates at 22 V with a 4 Ω load (P
approximately 486 mA. This ripple current can be used to determine the expected lifetime
of the SE capacitor. Most general purpose electrolytic capacitors (85 °C type) are capable
already of handling a 486 mA ripple current.
Both the ripple current and the voltage rating must be considered to prevent the capacitor
from failing.
A 15 nF SMD capacitor (NPO or X7R) is required to drive the high side N-channel
MOSFET. The bootstrap capacitor is charged by means of an internal diode between the
STAB1 (pin 25) and the BOOT1 (pin 28) at the moment that the low side MOSFET is on.
I
Impedance (Ω)
4
6
8
R
V
=
P
L
1 2 ⁄ V
-------------------- -
= load impedance (Ω)
= supply voltage (V) (V
2 R
shows the required SE capacitor values for a cut-off frequency of 60 Hz, 40 Hz
⋅
⋅
P
Values SE capacitor
L
in the application. This because the voltage at the SE capacitor can be
P
-- - ⋅
1
4
Rev. 01 — 12 December 2007
C15 / C24 (μF)
f
680
470
330
−3dB
rated
= 60 Hz
DDP
is equal to:
− V
SSP
)
f
1000
680
470
−3dB
TDA8932B/33(B) Class-D audio amplifier
P
). In these situations the peak voltage at
= 40 Hz
f
2200
1500
1000
−3dB
AN10436
© NXP B.V. 2007. All rights reserved.
= 20 Hz
rated
= 15 W) is
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