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LA4571MB

Low-voltage Headphone Amplifier for Stereo Audio

SANYO -> Panasonic 

LA4571MB

The internal circuit of the POWER MUTE pin is shown

in the following figure.

The power amplifier input pin, POWER IN1, is biased at

1.8V, and the output pins at 1.2V

Reference Voltage

The input to the voltage reference amplifier is a

voltage divided level from the supply voltage ripple

filter. The referecne voltage is given by 0.6 × VCC.

The supply voltage ripple filter requires the connection

of an external filter capacitor to RF REF. A large

capacitance results in a high ripple rejection ratio.

Noise filtering is achieved by the addition of a single

capacitor to VREF. Since the reference voltage ampli-

fier has a buffered output, this capacitor can be as low

as 1µF.

Design Notes

The preamplifier inputs should be connected to VREF

through a 2.2kΩ resistor if there is no tape head input

signal source.

The mute release time capacitor of the power amplifier

should be between 1.0 and 4.7µF. For VCC=3.0V and

C=2.2µF, the mute release time is 0.7s.

The ripple rejection ratio setting capacitor should be

between 2.2 and 33µF. For 2.2µF, the ripple rejection

ratio is 35dB, and for 22µF, it is 55dB.

When the output amplifier turns OFF, the protection

circuit shown in the following figure detects the falling

supply voltage and then mutes the power amplifier to

protect the device.

Sample Application Circuit

No.3534–8/9

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