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.
V
IN
T
UP
t
Vout
V
DD
/2
t
V
IN
T
DOWN
t
Figure 2 . How the volume change with respect to Up/Down timing cotrol
V
IN
UP
Vout
V
DD
/2
*T
T
2T
2T
t
t
~
300ms ± 20%
=
Figure 3. Up key be pressed continually
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V.1.0 Apr 30,2007
SAMHOP [ SAMHOP MICROELECTRONICS CORP. ]
