AA4838
Agamem Microelectronics Inc.
PRELIMINARY
AUDIO POWER AMPLIFIER
AVR=RFR/RIR and - AVL=RFL/RIL… (8)
Adjusting the input amplifier’s gain sets the minimum gain for that channel. Although the
single ended output of the Bridge Output Amplifiers can be used to drive line level outputs, it
is recommended that the R & L Dock Outputs simpler signal path be used for better
performance.
• BEEP DETECT FUNCTION
Computers and notebooks produce a system “beep“signal that drives a small speaker. The
speaker’s auditory output signifies that the system requires user attention or input. To
accommodate this system alert signal, the AA4838’s beep input pin is a mono input that
accepts the beep signal. Internal level detection circuitry at this input monitors the beep
signal’s magnitude. When a signal level greater than VDD/2 is detected on the BEEP IN pin,
the bridge output amplifiers are enabled. The beep signal is amplified and applied to the load
connected to the output amplifiers. A valid beep signal will be applied to the load even when
MUTE is active. Use the input resistors connected between the BEEP IN pin and the stereo
input pins to accommodate different beep signal amplitudes. These resistors (RBEEP) are
shown as 200kΩ devices in Figure 2. Use higher value resistors to reduce the gain applied
to the beep signal. The resistors must be used to pass the beep signal to the stereo inputs.
The BEEP IN pin is used only to detect the beep signal’s magnitude: it does not pass the
signal to the output amplifiers. The AA4838’s shutdown mode must be deactivated before a
system alert signal is applied to BEEP IN pin.
• MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the AA4838’s shutdown function.
Activate micro-power shutdown by applying VDD to the SHUTDOWN pin. When active, the
AA4838’s micro-power shutdown feature turns off the amplifier’s bias circuitry, reducing the
supply current. The logic threshold is typically VDD/2. The low 0.7 µA typical shutdown
current is achieved by applying a voltage that is as near as VDD as possible to the
SHUTDOWN pin. A voltage that is less than VDD may increase the shutdown current. There
are a few ways to control the micro-power shutdown. These include using a single-pole,
single-throw switch, a microprocessor, or a microcontroller. When using a switch, connect an
external 10kΩ pull-up resistor between the SHUTDOWN pin and VDD. Connect the switch
between the SHUTDOWN pin and ground. Select normal amplifier operation by closing the
switch. Opening the switch connects the SHUTDOWN pin to VDD through the pull-up resistor,
activating micro-power shutdown. The switch and resistor guarantee that the SHUTDOWN
pin will not float. This prevents unwanted state changes. In a system with a microprocessor or
a microcontroller, use a digital output to apply the control voltage to the SHUTDOWN pin.
Driving the SHUTDOWN pin with active circuitry eliminates the need for a pull up resistor.
• MODE FUNCTION
The AA4838’s MODE function has 2 states controlled by the voltage applied to the MODE pin.
Mode 0, selected by applying 0V to the MODE pin, forces the AA4838 to effectively function
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©Copyright Agamem Microelectronics Inc.
www.agamem.com.tw
2008/8/26
AGAMEM MICROELECTRONICS INCOPERATION RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE
TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. AGAMEM DOES NOT ASSUME ANY
LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCTS OR CIRCUIT DESRIBED HEREIN; NEITHER
DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS.
AGAMEM [ AGAMEM MICROELECTRONIC INC. ]
