APA2069 查看數據表（PDF） - Anpec Electronics

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APA2069

Stereo 2.6W Audio Power Amplifier (with DC_Volume Control)

Anpec Electronics 

APA2069

Application Descriptions (Cont.)

Input Capacitor, Ci (Cont.)

case, Ci and the minimum input impedance Ri (10kΩ)

form a high-pass filter with the corner frequency

determined in the follow equation:

FC(highpass)=

1

2πx10kΩxCi

(4)

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 10kΩ and the

specification calls for a flat bass response down to

100Hz. Equation is reconfigured as follow :

Ci=

1

2πx10kΩxfC

(5)

Consider to input resistance variation, the Ci is 0.16µF

so one would likely choose a value in the range

A further consideration for this capacitor is the leakage

path from the input source through the input network

(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 capacitor is the best choice. When polarized

capacitors 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 important

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 both the bypass and power

supply pins should be as close to the device as

possible. The effect of a larger bypass capacitor will

improve PSRR due to increased supply stability.

Typical applications employ a 5V regulator with 1.0µF

and a 0.1µF bypass capacitor as supply filtering. This

does not eliminate the need for bypassing the supply

nodes of the APA2069. The selection of bypass

capacitors, especially Cbypass, is thus dependent

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 (6) should be

maintained.

1

Cbypass x

125kΩ

<<

1

100kΩ x

Ci

(6)

The bypass capacitor is fed thru from a 125kΩ resistor

inside the amplifier and the 100kΩ is maximum input

resistance of (Ri+ Rf). Bypass capacitor, Cb, values of

3.3µF to 10µF ceramic or tantalum low-ESR capacitors

are recommended for the best THD and noise

performance.

The bypass capacitance also effects to the start up

time. It is determined in the following equation :

Tstart up = 5 x (Cbypass x 125KΩ)

(7)

Output Coupling Capacitor, Cc

In the typical single-supply SE configuration, an

output coupling capacitor (Cc) is required to block the

DC bias at the output of the amplifier thus preventing

DC currents in the load. As with the input coupling

capacitor, the output coupling capacitor and impedance

of the load form a high-pass filter governed by equation.

FC(highpass)=

1

2πRLCC

(8)

For example, a 330µF capacitor with an 8Ω speaker

would attenuate low frequencies below 60.6Hz. The

main disadvantage, from a performance standpoint, is

the load impedance is typically small, which drives

the low-frequency corner higher degrading the bass

response. Large values of CC are required to pass low

frequencies into the load.

Copyright © ANPEC Electronics Corp.

20

Rev. A.1 - Aug., 2005

www.anpec.com.tw

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