EUA6011AQIT1 データシートの表示（PDF） - Eutech Microelectronics Inc

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EUA6011AQIT1

3-W Stereo Audio Power Amplifier with Advanced DC Volume Control

Eutech Microelectronics Inc 

In this example, Ci is 56nF so one would likely choose a

value in the range of 56nF to 1µF. A further consideration

for this capacitor is the leakage path from the input source

through the input network (Ci) and the feedback network

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 than the source dc level. Note that it

is important to confirm the capacitor polarity in the

application.

EUA6011A

Output Coupling Capacitor, (CC)

For general signal-supply SE configuration, the 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 6.

fc(high)=

1

-------------------(6)

2π RLCC

Decoupling Capacitor, (CS)

The EUA6011A 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

oscillations for long lead lengths between

the amplifier and the speaker. The optimum decoupling is

achieved by using two capacitors of different types that

target different types 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 larger aluminum

electrolytic capacitor of 10µF or greater placed near the

audio power amplifier is recommended.

Bypass Capacitor, (CB)

The bypass capacitor, CB, is the most critical capacitor and

serves several important functions. During start-up or

recovery from shutdown mode, CB determines the rate at

which the amplifier starts up. The second function is to

reduce noise produced by the power supply caused by

coupling into the output drive signal. This noise is from the

midrail generation circuit internal to the amplifier, which

appears as degraded PSRR and THD+N. Bypass capacitor,

CB, values of 0.47µF to 1µF ceramic or tantalum low-ESR

capacitors are recommended for the best THD and noise

performance.

The main disadvantage, from a performance standpoint, is

the load impedances are 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. Consider the example where a

CC of 330µF is chosen and loads vary from 3Ω, 4Ω, 8Ω,

32Ω, 10kΩ, to 47kΩ. Table 3 summarizes the frequency

response characteristics of each configuration.

Table4. Common Load Impedances vs Low Frequency

Output characteristics in SE Mode

RL

CC

Lowest

Frequency

3Ω

330µF

161Hz

4Ω

330µF

120Hz

8Ω

330µF

60Hz

32Ω

330µF

15Hz

10000Ω

330µF

0.05Hz

47000Ω

330µF

0.01Hz

As Table 4 indicates, most of the bass response is

attenuated into a 4-Ω load and 8-Ω load is adequate,

headphone response is good, and drive into line level

inputs (a home stereo for example) is exceptional.

Using Low- ESR Capacitors

Low- ESR capacitors are recommended throughout this

applications section. A real (as opposed to ideal) capacitor

can be modeled simply as a resistor in series with an ideal

capacitor. The voltage drop across this resistor minimizes

the beneficial effects of the capacitor in the circuit. The

lower the equivalent value of this resistance the more the

real capacitor behaves like an ideal capacitor.

DS6011A Ver 1.0 Mar. 2006

18

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