No.7901-3/7

LA47536

Functional Description

1. Standby Switch Function (pin 4)

The pin 4 threshold voltage is set to be 2 VBE. When Vst is 2.0V or higher, the amplifier will be on, and when Vst is

0.7V or lower, the amplifier will be off. Note that pin 4 requires an operating current of at least 40µA.

2. Muting Function

The IC is set to the muted state by setting pin 22 to the ground potential. In this state, the audio output is muted. The

time constant with which the muting function operates is set by an external RC circuit, and this time constant

influences the pop noise that occurs when the amplifier is turned on or off.

The muting on and off times due to the recommended external component values (R=10k

Ω, C=3.3µF) are as follows.

Muting on time: 50ms

Muting off time: 20ms

3. Self-Diagnosis Function (Speaker burnout prevention)

During steady state operation, the LA47536 detects, internally, whether or not an abnormal amplifier output offset

has occurred, and outputs this signal from pin 25. Applications can prevent speaker burnout and other problems by

having the system microcontroller detect this pin 25 output signal and control either the standby state or the power

supply. (An abnormal output offset may be caused by, for example, input capacitor leakage current.)

The pin 25 signal is turned off by setting pin 1 to the ground potential.

4. Oscillator Stability

In some cases, parasitic oscillations may be induced by the PCB layout. This oscillation can be eliminated by adding

the components listed below. Note that the optimal capacitor value must be verified by testing in the actual mounted

state in the end product.

• Connect a capacitor and resistor (0.1µF and 2.2

Ω) in series between each output pin and ground.

5. Audio Quality (Low band)

The frequency characteristics in the low frequencies can be improved by making the capacitance of the input

capacitors variable.

The recommended capacitance is 2.2µF and smaller.

6. Protection Circuits

Do not ground the outputs with the STBY voltage at around 1.4V. Also, do not turn the IC off in the grounded state

with a time constant provided for the STBY voltage.

7. Pop Noise

Although the LA47536 includes an pop noise prevention circuit, pop noise can be reduced even further by using the

muting function as well.

• Activate the muting function at the same time as power is applied. Then, after the output DC potential has

stabilized, turn off the muting function.

• When turning the amplifier off, first turn on the muting function and then turn off the power supply.

These two methods are effective at minimizing pop noise.