APA4838 Ver la hoja de datos (PDF) - Anpec Electronics

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Fabricante

APA4838

Stereo 2.8W Audio Power Amplifier with DC Volume Control and Selectable Gain

Anpec Electronics 

APA4838

Application Descriptions (Cont.)

Docking Output Signal (Cont.)

Input Capacitor, Ci (Cont.)

Typical values for the output coupling capacitors are

0.33µF to 1.0µF. If polarized coupling capacitors are

used, connect their ’+’ terminals to the respective

output pin.

The Right Dock and Left Dock channel outputs sig-

nal are also used to driving internal volume control

amplifier.

Input Capacitor, Ci

In the typical application an input capacitor, Ci, is re-

quired to allow the amplifier to bias the input signal to

the proper DC level for optimum operation. In this

case, Ci and the minimum input impedance Ri form a

high-pass filter with the corner frequency determined

in the follow equation:

FC(highpass)=

1

2πRiCi

(3)

The value of Ci is important to consider as it directly

affects the low frequency performance of the circuit.

Consider the example where Ri is 100kΩ and the

specification calls for a flat bass response down to

40Hz. Equation is reconfigured as follow:

Ci=

1

2πRifC

(4)

Consider to input resistance variation, the Ci is 0.04µF

so one would likely choose a value in the range of

0.1µF to 1.0µF.

A further consideration for this capacitor is the leak-

age path from the input source through the input net-

work (Ri+Rf, Ci) to the load.

This leakage current creates a DC offset voltage at

the input to the amplifier that reduces useful

headroom, especially in high gain applications. For

this reason a low-leakage tantalum or ceramic ca-

pacitor is the best choice. When polarized capaci-

tors are used, the positive side of the capacitor should

face the amplifier input in most applications as the

DC level there is held at VDD/2, which is likely higher

that the source DC level. Please note that it is impor-

tant to confirm the capacitor polarity in the application.

Effective Bypass Capacitor, Cbypass

As other power amplifiers, proper supply bypassing

is critical for low noise performance and high power

supply rejection.

The capacitors located on the bypass and power

supply pins should be as close to the device as

possible. The effect of a larger half supply bypass

capacitor will improve PSRR due to increased half-

supply stability. Typical application employ a 5V regu-

lator with 1.0µF and a 0.1µF bypass as supply filtering.

This does not eliminate the need for bypassing the

supply nodes of the APA4838. The selection of by-

pass capacitors, especially Cbypass, is thus depen-

dent upon desired PSRR requirements, click and pop

performance.

To avoid start-up pop noise occurred, the bypass

voltage should rise slower than the input bias voltage

and the relationship shown in equation (5) should be

maintained.

1

Cbypass x 125kΩ

<<

1

RiCi

(5)

Copyright  ANPEC Electronics Corp.

19

Rev. A.1 - Apr., 2003

www.anpec.com.tw

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