APA0715 데이터 시트보기 (PDF) - Anpec Electronics

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APA0715

3W Mono Fully Differential Audio Power Amplifier

Anpec Electronics 

APA0715

Application Information (Cont.)

Power Supply Decoupling Capacitor (Cs) (Cont.)

as low as possible. Power supply decoupling also pre-

vents the oscillations being caused by long lead length

between the amplifier and the speaker.

The optimum decoupling is achieved by using two differ-

ent types of capacitors that target on different types of

noises 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, is placed as close as possible to the de-

vice 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.

Fully Differential Amplifier Efficiency

The traditional class AB power amplifier efficiency can be

calculated starts out as being equal to the ratio of power

from the power supply to the power delivered to the load.

The following equations are the basis for calculating the

amplifier efficiency.

Efficiency (η) = PO

(4)

PSUP

where:

PO

=

VOrms 2

RL

=

VP2

2RL

VOrms = VP

2

PSUP = VDDXIDD（AVG）＝2VπDRDVL PP

(5)

IDD（AVG)

=

2VP

πRL

So the Efficiency (η) is:

Efficiency (η) =

πVP

π

＝

2PORL

(6)

4VDD

4VDD

Table 1 calculates efficiencies for four different output

power levels. Note that the efficiency of the amplifier is

quite low for lower power levels and rises sharply as

power to the load is increased resulting in nearly flat in-

ternal power dissipation over the normal operating range.

Note that the internal dissipation at full output power is

less than the dissipation in the half power range. Calcu-

lating the efficiency for a specific system is the key to

proper power supply design. For a Mono 1W audio sys-

tem with 8Ω loads and a 5V supply, the maximum draw

on the power supply is almost 1.63W.

RL (Ω) PO (W)

0.25

0.50

8

1

1.6

0.4

1.2

4

2

2.6

0.5

3

1

2

3

Efficiency

(%)

30.1

43.1

61.5

77.7

27.5

48.1

62.4

74.1

27.5

38.7

55.1

66.8

IDD(A)

0.17

0.23

0.33

0.43

0.29

0.51

0.66

0.70

0.37

0.52

0.74

0.92

PD (W) PSUP (W)

0.58

0.66

0.63

0.46

1.06

1.30

1.21

0.91

1.32

1.58

1.63

1.49

0.83

1.16

1.63

2.06

1.46

2.50

3.21

3.51

1.82

2.58

3.63

4.49

Table 1: Efficiency vs. Output Power in 5-V Differential

Amplifier Syetems

A final point to remember about linear amplifiers (either

SE or Differential) is how to manipulate the terms in the

efficiency equation to an utmost advantage when possible.

Note that in equation, VDD is in the denominator. This indi-

cates that as VDD goes down, efficiency goes up. In other

words, use the efficiency analysis to choose the correct

supply voltage and speaker impedance for the application.

Layout Recommendation

1. All components should be placed close to the APA0715.

For example, the input capacitor (Ci) should be close

to APA0715’s input pins to avoid causing noise cou-

pling to APA0715’s high impedance inputs; the

decoupling capacitor (C ) should be placed by the

s

APA0715’s power pin to decouple the power rail noise.

2. The output traces should be short, wide ( >50mil), and

symmetric.

3. The input trace should be short and symmetric.

4. The power trace width should greater than 50mil.

5. The MSOP-8P and DFN3x3-8 Thermal PAD should be

soldered on PCB, and the ground plane needs sol-

dered mask (to avoid short circuit) except the Thermal

PAD area.

Copyright © ANPEC Electronics Corp.

17

Rev. A.1 - Dec., 2008

www.anpec.com.tw

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