SAMHOP Microelectronics Corp.
3W STEREO AUDIO POWER AMPLIFIER WITH ADVANCED DC VOLUME CONTROL
SHUTDOWN MODES
The SM7512 employs a shutdown mode of operation designed to reduce supply current (IDD) to the absolute
minimum level during periods of nonuse for battery-power conservation. The SHUTDOWN input terminal should
be held high during normal operation when the amplifier is in use. Pulling SHUTDOWN low causes the outputs
to mute and the amplifier to enter a low-current state, IDD= 20μA. SHUTDOWN should never be left
unconnected because amplifier operation would be unpredictable.
VOLUME OPERATION
The VOLUME controls the BTL volume when driving speakers and the SE volume when driving headphones.
The pin is controlled with a dc voltage, which should not exceed VDD.
When driving speakers in BTL mode, the VOLUME pin is the only pin that controls the gain. Table 1 shows the
gain for the BTL mode. The voltage listed in the table are for VDD=5V. For a different VDD, the values in the
table scale linearly. If VDD=4V, multiply all the voltages in the table by 4V/5V or 0.8.
Some audio systems require that the gain be limited in the single-ended mode to a level that is comfortable for
headphone listening. Most volume control devices only have one terminal for setting the gain. For example, if
the speaker gain is 20 dB, the gain in the headphone channel is fixed at 14 dB.
Table 1 show a range of voltages for each gain step. There is a gap in the voltage between each gain step.
This gap represents the hysteresis about each trip point in the internal comparator. The hysteresis ensures that
the gain control is monotonic and does not oscillate from one gain step to another. If a potentiometer is used to
adjust the voltage on the control terminals, the gain increases as the potentiometer is turned in one direction
and decreases as it is turned back the other direction. The trip point, where the gain actually changes, is
different depending on whether the voltage is increased or decreased as a result of the hysteresis about each
trip point. The gaps can also be thought of as indeterminate states where the gain could be in the next higher
gain step or the lower gain step depending on the direction the voltage is changing. If using a DAC to control
the volume, set the volume, set the voltage in the middle of each range to ensure that the desired gain is
achieved.
TABLE OF GRAPHS
FIGURE
vs Frequency
3,4,5
6,7,8
9,10
11,12
13
THD+N Total harmonic distortion plus noise(BTL)
vs Output power
Closed loop response
Crosstalk
vs Frequency
vs Frequency
PSRR Power supply ripple rejection(BTL)
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V.1.4 Revised May 28,2007
SAMHOP [ SAMHOP MICROELECTRONICS CORP. ]
