AA4838
Agamem Microelectronics Inc.
PRELIMINARY
AUDIO POWER AMPLIFIER
■
TRUTH TABLE FOR LOGIC INPUTS (Note)
Gain Mode Headphone Mute Shutdown Output Stage
Set To
DC Volume
Output Stage
Configuration
Sel
Sense
0
0
0
0
1
1
1
1
X
X
0
0
1
1
0
0
1
1
X
X
0
1
0
1
0
1
0
1
X
X
0
0
0
0
0
0
0
0
1
X
0
0
0
0
0
0
0
0
0
1
Internal Gain
Internal Gain
Internal Gain
Internal Gain
External Gain
External Gain
External Gain
External Gain
Muted
Fixed
Fixed
Adjustable
Adjustable
Fixed
BTL
SE
BTL
SE
BTL
SE
BTL
SE
Fixed
Adjustable
Adjustable
X
Muted
X
Shutdown
X
Note: If system beep is detected on the Beep In pin, the system beep will be passed through
the bridged amplifier regardless of the logic of the Mute and HP sense pins.
■ APPLICATION INFORMATION
• PCB LAYOUT AND SUPPLY REGULATION CONSIDERATIONS FOR DRIVING 3Ω AND
4Ω LOADS
Power dissipated by a load is a function of the voltage swing across the load and the load’s
impedance. As load impedance decreases, load dissipation becomes increasingly dependent
on the interconnect (PCB trace and wire) resistance between the amplifier output pins and the
load’s connections. Residual trace resistance causes a voltage drop, which results in power
dissipated in the trace and not in the load as desired. For example, 0.1Ω trace resistance
reduces the output power dissipated by a 4Ω load from 2.1W to 2.0W. This problem of
decreased load dissipation is exacerbated as load impedance decreases. Therefore, to
maintain the highest load dissipation and widest output voltage swing, PCB traces that
connect the output pins to a load must be as wide as possible. Poor power supply regulation
adversely affects maximum output power. A poorly regulated supply’s output voltage
decreases with increasing load current. Reduced supply voltage causes decreased headroom,
output signal clipping, and reduced output power. Even with tightly regulated sup- plies, trace
resistance creates the same effects as poor supply regulation. Therefore, making the power
supply traces as wide as possible helps maintain full output voltage swing.
• BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 2, the AA4838 output stage consists of two pairs of operational amplifiers,
forming a two-channel (channel A and channel B) stereo amplifier. (Though the following
discusses channel A, it applies equally to channel B.) Figure 2 shows that the first amplifier’s
8
©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. ]
