APA0710XAI datasheet(22/29 Pages) ANPEC

22 / 29 page

Rev. A.5 - Oct., 2005

APA0710/0711

www.anpec.com.tw

Effective Bypass Capacitor, Cbypass (Cont.)

(4)

Application Descriptions (Cont.)

The bypass capacitor is fed from a 80k

Ω resistor

inside the amplifier. Bypass capacitor, Cbypass, values

of 0.1

µF to 2.2µF 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 80k

Ω)

(5)

Output Coupling Capacitor, Cc (for APA0710 only)

In the typical single-supply (SE) configuration on a

APA0710, 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)=

πRLCC

(6)

For example, a 330

µF 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

C are required to pass low

frequencies into the load.

)

80k

Cbypass

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 (4) should be

maintained.

Power Supply Decoupling, Cs

The APA0710/1 is a high-performance CMOS audio

amplifier that requires adequate power supply

decoupling to ensure the output total harmonic

distortion (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 different type

of noise on the power supply leads. For higher frequency

transients, spikes, or digital hash on the line, a good

low equiv alent-series-resistance (ESR) ceramic

capacitor, typically 0.1

µF placed as close as possible

to the device V

DD lead works best. For filtering lower-

frequency noise signals, a large aluminum electrolytic

capacitor of 10

µF or greater placed near the audio

power amplifier is recommended.

Optimizing Depop Circuitry

Circuitry has been included in the APA0710/1 to

minimize the amount of popping noise at power-up

and when coming out of shutdown mode. Popping

occurs 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.

Although the bypass pin current source cannot be

modified, the size of Cbypass can be changed to alter

the device turn-on time and the amount of clicks and

pops. By increasing the value of Cbypass, turn-on pop

can be reduced. However, the tradeoff for using a larger

bypass capacitor is to increase the turn-on time for

this device. There is a linear relationship between the

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