MP7770 –2 X 45W STEREO SE OR 90W MONO BTL CLASS D AUDIO AMPLIFIER

MP7770 Rev.1.0

www.MonolithicPower.com

16

12/4/2012

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© 2012 MPS. All Rights Reserved.

APPLICATION INFORMATION

Component Selection

The MP7770 uses a minimal number of external

components to complete a stereo SE or mono

BTL Class D audio amplifier. The circuit in Figure

6 (stereo SE application circuit) and Figure 7

(mono BLT application circuit) are optimized for a

24V power supply. This circuit should be suitable

for most applications. Use the following sections

to design custom circuits.

Setting the Voltage Gain

The maximum output-voltage swing is limited by

the power supply. To achieve the maximum

output power, set the gain such that the

maximum input signal results in the maximum

output voltage swing.

For a single-ended (SE) output configuration, the

bridge-tied-load (BTL) output configuration, the

peak input voltage, the maximum voltage gain is:

OUT(PK )

V

IN(PK )

V

A(MAX)

V



This voltage-gain setting results in the peak

output voltage approaching its maximum for the

maximum input signal. In some cases the

amplifier is allowed to overdrive slightly, allowing

the THD to increase at high power levels, and so

Setting the Switching Frequency

The idle switching frequency (the switching

frequency when no audio input is present) is a

function of several variables: The supply voltage

in greater inductor ripple, causing more quiescent

output voltage ripple, and increasing the output

noise

and

distortion.

Higher

switching

frequencies result in greater power loss. The

optimum

quiescent

switching

frequency

is

approximately 600kHz. When used to drive

stereo speakers in single-ended configuration,

set right channel to an idle switching frequency

greater than 50kHz plus the left channel’s

switching frequency by using a different timing

recommended SE output configuration design,

and Table 3 for recommended BTL output

configuration design.

Table 2: Switching Frequency Setting For SE

Output Configuration

(V)

Gain

(V/V)

(kΩ)

(kΩ)

Left

channel

Right

channel

(nF)

(kHz)

(nF)

(kHz)

12

10

100

10

2.2

635

1.8

705

12

20

100

4.99

2.2

635

1.8

705

24

10

75

7.5

5.6

700

4.7

740

24

20

150

7.5

2.2

780

2.7

665

30

10

51

5.1

8.2

780

10

680

30

20

150

7.5

3.3

710

2.7

780

30

30

150

4.99

3.3

710

2.7

780

34

10

51

5.1

10

785

12

610

34

20

100

4.99

4.7

780

5.6

740

34

30

150

4.99

3.9

700

3.3

775

Table 3: Switching Frequency Setting for BTL

Output Configuration

(V)

Gain

(V/V)

(kΩ)

(kΩ)

(nF)

(kHz)

12

10

100

10

2.2

435

12

20

100

4.99

2.2

435

12

30

150

4.99

1.0

440

24

10

100

10

3.3

490

24

20

100

4.99

2.2

570

24

30

150

4.99

1.5

480

30

10

100

10

2.2

465

30

20

100

4.99

3.3

535

30

30

150

4.99

2.2

450

34

10

100

10

3.3

560

34

20

100

4.99

3.3

560

34

30

150

4.99

2.2

470