Applications Information

Suggested Application Circuit

The LM4663 achieves its specified performance using the

recommended application circuit shown in Figure 1. The cir-

cuit provides full access to the stereo 2W/channel power am-

plifiers and the 80mW/channel stereo headphone amplifier.

The HPSELECT (headphone select ) input is controlled by a

stereo mini-plug/jack with additional control contact. Other

applications of this device may use external generated logic

signals to control this function.

Control Pins

The LM4663 has three control pins: INSEL, SD, and HPSEL.

The INSEL pin is used to select between the two stereo in-

puts, V

supply selects V

V

the SD to the positive supply. Applying the positive supply to

the HPSEL pin selects the headphone amplifiers and

grounding the HPSEL pin selects the Class D amplifiers.

Table 1 is a summary of the function selected when applying

ground or V

TABLE 1. Function selected when applying V

GND to the INSEL, SD, and HPSEL control pins.

Control

Function

Pin

Apply GND

Apply V

DD

INSEL

10

V

V

SD

9

Full power

operation

Micropower

shutdown

HPSEL

16

Deactivate

headphone amps

and activate

Class D amps

Deactivate Class

D amps and

activate

headphone amps

Output Filters

The LM4663’s 2W power amplifiers use a Class D switching

topology that requires a filter between the amplifier outputs

and the load. The balanced, L-C filters shown in Figure 1 use

component values recommended for a maximally flat magni-

tude in the pass-band and a cut-off frequency of 18kHz with

a load impedance of 4

Ω. We do not recommend omitting the

filter because considerable out-of-band energy is present in

the Class D output waveform. This energy would be dissi-

pated in the load impedance’s resistive component, which

diminishes efficiency.

DS101269-3

FIGURE 1. Operating on a single 5V supply, this recommended application circuit is a complete solution with 2W

Class D amplifiers that drive 4

Ω speakers and 80mW amplifiers drive 32Ω headphones.

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