SAMHOP Microelectronics Corp.

3W STEREO AUDIO POWER AMPLIFIER WITH UP / DOWN GAIN CONTROL

VOLUME CONTROL

The output volume of SM7513 is respectively controlled by two input pins, UP and Down pin. The UP pin

controls the volume increment, and the DOWN pin controls the volume decrement. It increases/decreases ±2dB

each step. Both are all active high. The SM7513 built-in a RC oscillator and generates a based frequency for

volume output register to count increasingly or decreasingly. It starts to count when the UP/DOWN pin is

pressed. If the voltage on UP/DOWN pin is disappeared in specific unit period, the volume increment or

decrement is not accepted, which means no action, keeps the original voltage and clears the value in count

register. Therefore, there is no increment or decrement to make the volume uncertainly. After power on or

shutdown, SM7513 will has -4dB±2dB initial gain.

The mapping between output volume increment / decrement and active unit period is shown in Figure 2. When

the UP Key keeps high for one active unit period, the output gain increases 2db after the Key is released. When

the UP Key keeps low and the DOWN Key become high level for one active unit period, the output gain

decreases 2db.

The action of pressed the UP/DOWN Key continually is shown in Figure 3. The gain is increased/ decreased

after one unit periods. If the Key is continually be pressed more than two unit periods, the gain is increased/

decreased until to maximum 20dB or -65dB.

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T

UP

t

Vout

DOWN

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Figure 2 . How the volume change with respect to Up/Down timing cotrol

UP

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2T

2T

Vout

Figure 3. Up key be pressed continually

* T

300ms ± 20%

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V.1.0 Apr 30,2007