Agamem Microelectronics Inc.

AA4838

PRELIMINARY

AUDIO POWER AMPLIFIER

©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.

8

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TRUTH TABLE FOR LOGIC INPUTS (Note)

Gain

Sel

Mode Headphone

Sense

Mute Shutdown Output Stage

Set To

DC Volume

Output Stage

Configuration

0

0

0

0

0

Internal Gain

Fixed

BTL

0

0

1

0

0

Internal Gain

Fixed

SE

0

1

0

0

0

Internal Gain

Adjustable

BTL

0

1

1

0

0

Internal Gain

Adjustable

SE

1

0

0

0

0

External Gain

Fixed

BTL

1

0

1

0

0

External Gain

Fixed

SE

1

1

0

0

0

External Gain

Adjustable

BTL

1

1

1

0

0

External Gain

Adjustable

SE

X

X

X

1

0

Muted

X

Muted

X

X

X

X

1

Shutdown

X

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.

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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