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LA4905 Datasheet(Fiches technique) 6 Page - Sanyo Semicon Device

Numéro de pièce LA4905
Description  17-W, 2-Channel BTL AF High-Efficiency Power Amplifier for Car Stereo Systems
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Fabricant  SANYO [Sanyo Semicon Device]
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2. IC Internal Characteristics and Usage Notes
Switching Regulator
• To reduce power dissipation, the LA4905 includes a signal-following type switching regulator. When there is no input
signal, the self-excited oscillator operates at about 100 kHz.
• It is desirable for the amplifier block to be separated as far as possible from the tuner block to prevent interference from
extraneous radiation within the set. Also, when designing the printed circuit board layout, the pattern lines for the
switching regulator components should be made as short and as broad as possible.
• To prevent degradation of the characteristics of the LA4905 itself, the separation between the switching regulator
components and the IC input block (the input block pattern, the input capacitors, and the beep capacitor) should be at
least 1.5 cm.
Standby Function
• Pin 21 is the standby switch pin. The amplifier is turned
on by applying a voltage of about 3 V or higher through
an external resistor (R1).
• The value of R1 must be determined, using the following
formula, so that the pin 5 influx current remains under
500 µA if a voltage in excess of 13.2 volts is applied as
the standby switch voltage.
applied voltage – 1.4 V
R1 = —————————— – 10 k
500 µA
BEEP Pin (pin 4)
• If the BEEP pin is used, use a value for R102 shown in
the figure that is under 100
Ω and is as small as possible
to prevent degradation of the IC output noise voltage
Protection Circuits
• The LA4905 includes a built-in thermal protection
circuit to prevent destruction or degradation if the IC
generates abnormal amounts of heat. The thermal
protection circuit controls the IC so that the output is
gradually lowered if the IC junction temperature (Tj)
increases to about 160°C due to an insufficient heat sink
or other reason.
• The overvoltage protection circuit operates if the VCC
voltage exceeds a value of about 20 volts.
• Although the LA4905 includes an on-chip protection
circuit for shorts to VCC and shorts to ground, it does not
include a load shorted protection circuit. The idea behind
this design is that the thermal protection circuit will
protect the IC against load shorting. However, since load
shorting can also cause heating in external transistors and
coils, designs should take load shorting into
Other Notes
• Pin 22 is an NC pin, and is not connected within the
No. 5504-6/10

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