LA4917H Datasheet, PDF (5/8 Pages) Sanyo Semicon Device – Monolithic Linear IC Audio Output for TV application High-Effciency Two-Channel 7W BTL Power Amplifier ICs

LA4917H
External Component Descriptions
C1 :
This capacitor functions as a ripple filter. A value of 47µF is recommended.
C2 :
This capacitor sets the amplifier startup wait time. A value of 22µF is recommended. (With this
value, the startup wait time will be about 0.7 seconds.) Although the startup wait time can be made
shorter by reducing the value of this capacitor, this can result in impulse noise appearing in the
output. We recommend always using a value larger than 10µF.
C3 and C5 :
Input capacitors. A value of 22µF is recommended. Note that if made variable, a value of 3.3µF or
lower should be used due to impulse noise considerations.
C4 :
This capacitor is the input reference amplifier capacitor, and the value must be the same as that of
C3 and C5.
C6 and R1 :
Smoothing capacitor for the switching regulator output. The LA4917H adopts a self-excited
oscillation switching regulator design. Since this capacitor influences the stability of the
self-excited oscillation, we recommend keeping the equivalent series resistance at high
frequencies low (roughly 3Ω or lower) and using a capacitor with good thermal characteristics.
For similar reasons, a value of 2.2Ω should be used for R1.
C7, C8, C9, and C10 : Oscillation prevention capacitors. We recommend using polyester film capacitors (Mylar
capacitor) with good thermal characteristics for these capacitors. These are used together with R2,
R3, R4, and R5.
C11 :
Switching regulator oscillation prevention capacitor. We recommend a value of 1000pF.
C12 :
Power supply capacitor
Tr1 and *RB :
This is an external switching transistor. Since the collector current has a peak of about 1.5A, we
recommend using a transistor in the fT = 30 to 50MHz range according to the current capacity
required. Note that if a transistor with an fT of 100MHz or higher is used, oscillation may be
induced in the switching waveform. Therefore in this case a base resistor, *RB, with a resistance of
about 10Ω must be added and the circuit adjusted so that oscillation does not occur.
L1 :
We recommend a coil inductance in the range 150 to 220µH.
D1 :
This is a flywheel diode that absorbs the coil energy. We recommend the use of a Schottky barrier
diode with a low VF.
Notes on the Switching Regulator (Pins 22 to 24)
• The LA4917H includes a signal-following self-excitation switching regulator to hold power consumption to a
minimum. The self-excitation oscillation frequency when no signal is input will be in the range from about 130 to
170kHz.
• Transistor Tr1 is an external switching transistor.
We recommend using a device with IC = 2.5A and fT = 30
to 50MHz
If a transistor with an fT of 100MHz or higher is used,
oscillation may be induced in the switching waveform.
Therefore in this case a base resistor (RB, about 10Ω) must
be added and the circuit adjusted so that oscillation does not
occur.
• C6 is used to smooth the output of the switching regulator.
Since this capacitor influences the stability of the
self-excited oscillation, we recommend keeping the
equivalent series resistance at high frequencies low and
using a capacitor with good thermal characteristics. The
recommended value for this capacitor is 2.2µF.
Note that for similar reasons, a resistor with a value of 2.2Ω
should be used for R1.
24
SW B
23
SW E
22
SW OUT
*RB
10Ω
L1
180µH
Tr1
Switching
Transistor
I _C =2.5A
f _T = 30 to 50MHz
D1
Flywheel
Diode
C6
2.2µF
/25V
R1
2.2 Ω
• D1 is a flywheel diode that absorbs the coil energy. We
recommend the use of a Schottky barrier diode with a low
VF.
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