LM4849 datasheet(17/19 Pages) NSC

17 / 19 page

Application Information (Continued)

VOLUME CONTROL (Table 2)

Gain

(dB)

Voltage Range (% of Vdd)

Voltage Range (Vdd = 5)

Voltage Range (Vdd = 3)

Low

High

Recommended Low

High

Recommended Low

High

Recommended

77.5%

100.00%

100.000%

3.875

5.000

2.325

3.000

-1

75.0%

78.5%

76.875%

3.750

3.938

3.844

2.250

2.363

2.306

-2

72.5%

76.25%

74.375%

3.625

3.813

3.719

2.175

2.288

2.231

-3

70.0%

73.75%

71.875%

3.500

3.688

3.594

2.100

2.213

2.156

-4

67.5%

71.25%

69.375%

3.375

3.563

3.469

2.025

2.138

2.081

-5

65.0%

68.75%

66.875%

3.250

3.438

3.344

1.950

2.063

2.006

-6

62.5%

66.25%

64.375%

3.125

3.313

3.219

1.875

1.988

1.931

-8

60.0%

63.75%

61.875%

3.000

3.188

3.094

1.800

1.913

1.856

-10

57.5%

61.25%

59.375%

2.875

3.063

2.969

1.725

1.838

1.781

-12

55.0%

58.75%

56.875%

2.750

2.938

2.844

1.650

1.763

1.706

-14

52.5%

56.25%

54.375%

2.625

2.813

2.719

1.575

1.688

1.631

-16

50.0%

53.75%

51.875%

2.500

2.688

2.594

1.500

1.613

1.556

-18

47.5%

51.25%

49.375%

2.375

2.563

2.469

1.425

1.538

1.481

-20

45.0%

48.75%

46.875%

2.250

2.438

2.344

1.350

1.463

1.406

-22

42.5%

46.25%

44.375%

2.125

2.313

2.219

1.275

1.388

1.331

-24

40.0%

43.75%

41.875%

2.000

2.188

2.094

1.200

1.313

1.256

-26

37.5%

41.25%

39.375%

1.875

2.063

1.969

1.125

1.238

1.181

-28

35.0%

38.75%

36.875%

1.750

1.938

1.844

1.050

1.163

1.106

-30

32.5%

36.25%

34.375%

1.625

1.813

1.719

0.975

1.088

1.031

-32

30.0%

33.75%

31.875%

1.500

1.688

1.594

0.900

1.013

0.956

-34

27.5%

31.25%

29.375%

1.375

1.563

1.469

0.825

0.937

0.881

-36

25.0%

28.75%

26.875%

1.250

1.438

1.344

0.750

0.862

0.806

-39

22.5%

26.25%

24.375%

1.125

1.313

1.219

0.675

0.787

0.731

-42

20.0%

23.75%

21.875%

1.000

1.188

1.094

0.600

0.712

0.656

-45

17.5%

21.25%

19.375%

0.875

1.063

0.969

0.525

0.637

0.581

-47

15.0%

18.75%

16.875%

0.750

0.937

0.844

0.450

0.562

0.506

-51

12.5%

16.25%

14.375%

0.625

0.812

0.719

0.375

0.487

0.431

-56

10.0%

13.75%

11.875%

0.500

0.687

0.594

0.300

0.412

0.356

-61

7.5%

11.25%

9.375%

0.375

0.562

0.469

0.225

0.337

0.281

-66

5.0%

8.75%

6.875%

0.250

0.437

0.344

0.150

0.262

0.206

-78

0.0%

6.25%

0.000%

0.000

0.312

0.000

0.187

0.000

AUDIO POWER AMPLIFIER DESIGN

Audio Amplifier Design: Driving 1W into an 8

Ω Load

The following are the desired operational parameters:

Power Output:

1 W

RMS

Load Impedance:

Ω

Input Level:

1 V

RMS

Input Impedance:

20 k

Ω

Bandwidth:

100 Hz−20 kHz ± 0.25 dB

The design begins by specifying the minimum supply voltage

necessary to obtain the specified output power. One way to

find the minimum supply voltage is to use the Output Power

vs Supply Voltage curve in the Typical Performance Char-

acteristics section. Another way, using Equation (11), is to

calculate the peak output voltage necessary to achieve the

desired output power for a given load impedance. To ac-

count for the amplifier’s dropout voltage, two additional volt-

ages, based on the Dropout Voltage vs Supply Voltage in the

Typical Performance Characteristics curves, must be

added to the result obtained by Equation (11). The result is

Equation (12).

(9)

≥ (V

OUTPEAK+(VODTOP +VODBOT))

(10)

The Output Power vs Supply Voltage graph for an 8

Ω load

indicates a minimum supply voltage of 4.6V. This is easily

met by the commonly used 5V supply voltage. The additional

voltage creates the benefit of headroom, allowing the

LM4849 to produce peak output power in excess of 1W

without clipping or other audible distortion. The choice of

LM4849 Datasheet(PDF) 17 Page - National Semiconductor (TI)

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