APA4838RI Ver la hoja de datos (PDF) - Anpec Electronics

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APA4838RI

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

Anpec Electronics 

APA4838

Application Descriptions (Cont.)

Effective Bypass Capacitor, Cbypass (Cont.)

Power Supply Decoupling, Cs

The bypass capacitor is fed from a 125kΩ resistor

inside the amplifier. Bypass capacitor, Cbypass, val-

ues 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)

(6)

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 pre-

venting 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 gov-

erned by equation.

FC(highpass)=

1

2πRLCC

(7)

The APA4838 is a high-performance CMOS audio

amplifier that requires adequate power supply

decoupling to ensure the output total harmonic dis-

tortion (THD) is as low as possible. Power supply

decoupling also prevents the oscillations causing by

long lead length between the amplifier and the

speaker. The optimum decoupling is achieved by

using two different type capacitors that target on dif-

ferent type of noise on the power supply leads. For

higher frequency transients, spikes, or digital hash

on the line, a good low equivalent-series-resistance

(ESR) ceramic capacitor, typically 0.1µF placed as

close as possible to the device VDD lead works best.

For filtering lower-frequency noise signals, a large

aluminum electrolytic capacitor of 10µF or greater

placed near the audio power amplifier is

recommended.

Optimizing Depop Circuitry

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 C are required to pass

C

low frequencies into the load.

Circuitry has been included in the APA4838 to mini-

mize the amount of popping noise at power-up and

when coming out of shutdown mode. Popping oc-

curs whenever a voltage step is applied to the

speaker. In order to eliminate clicks and pops, all

capacitors must be fully discharged before turn-on.

Rapid on/off switching of the device or the shutdown

function will cause the click and pop circuitry. The

value of Ci will also affect turn-on pops. (Refer to

Effective Bypass Capacitance) The bypass voltage

rise up should be slower than input bias voltage.

Copyright  ANPEC Electronics Corp.

20

Rev. A.1 - Apr., 2003

www.anpec.com.tw

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