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| 型號(hào)： | EV0030 |
| 廠商： | Monolithic Power Systems, Inc. |
| 英文描述： | 20W Class D Mono Single Ended Audio Amplifer |
| 中文描述： | D類單聲道20瓦單端音頻放大器 |
| 文件頁(yè)數(shù)： | 6/11頁(yè) |
| 文件大?。?/td> | 344K |
| 代理商： | EV0030 |
MP7720 – 20W CLASS D MONO SINGLE ENDED AUDIO AMPLIFIER
MP7720 Rev. 1.9
3/13/2006
www.MonolithicPower.com
6
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
2006 MPS. All Rights Reserved.
APPLICATION INFORMATION
COMPONENT SELECTION
The MP7720 uses a minimum number of
external components to complete a Class D
audio amplifier. The circuit of Figure 1 is
optimized for a 24V power supply and a 1.5V
RMS maximum input signal. This circuit should
be suitable for most applications. However, if
this circuit is not suitable, use the following
sections to determine how to customize the
amplifier for a particular application.
Setting the Voltage Gain
The maximum output voltage swing is limited by
the power supply. To achieve the maximum
power out of the MP7720 amplifier, set the gain
such that the maximum input signal results in
the maximum output voltage swing.
The maximum output voltage swing is ±V
DD
/2.
For a given input signal voltage, where V
IN
(pk)
is the peak input voltage, the maximum voltage
gain is:
)
pk
(
V
2
V
)
MAX
(
A
IN
DD
V
×
=
This voltage gain setting results in the peak
output voltage approaching it’s 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 a higher gain than A
V
(max) is
required.
Setting the Switching Frequency
The idle switching frequency is a function of
V
DD
, the capacitor C3 and the feedback resistor
R4. Lower switching frequencies result in more
inductor ripple, causing more quiescent output
voltage ripple and increasing the output noise
and distortion. Higher switching frequencies
result in more power loss. The optimum
quiescent switching frequency is approximately
600KHz to 700KHz. Refer to the Operating
Specifications for recommended values.
Table 1—Switching Frequency vs. Integrating
Capacitor and Feedback Resistor (see Figure 1)
Gain
(V/V)
Gain
(dB)
R
4
(k
)
R
1
(k
)
C
3
F
SW
V
DD
(V)
3.9
15.0
39
10
6.8nF
660KHz
12
8.2
18.3
82
10
3.3nF
660KHz
12
8.3
21.5
39
4.7
6.8nF
660KHz
12
12.0
21.6
120
10
2.2nF
610KHz
12
17.4
24.8
82
4.7
3.3nF
660KHz
12
25.5
28.1
120
4.7
2.2nF
610KHz
12
5.6
15.0
56
10
8.2nF
670KHz
24
8.2
18.3
82
10
5.6nF
720KHz
24
11.9
21.5
56
4.7
8.2nF
670KHz
24
12.0
21.6
120
10
4.7nF
620KHz
24
17.4
24.8
82
4.7
5.6nF
720KHz
24
25.5
28.1
120
4.7
4.7nF
620KHz
24
33.0
30.4
330
10
1.8nF
700KHz
24
Choosing the LC Filter
The Inductor-Capacitor (LC) filter converts the
pulse train at SW to the output voltage that
drives the speaker. Typical values for the LC
filter are shown in Figure 1, 10μH inductor and
0.47μF capacitor.
The characteristic frequency of the LC filter
needs to be high enough to allow high
frequency audio to the output, yet needs to be
low enough to filter out high frequency products
of the pulses from SW. The characteristic
frequency of the LC filter is:
(
)
2
1
0
LC
2
1
f
π
=
The voltage ripple at the output is approximated
by the equation:
×
SW
0
DD
RIPPLE
V
f
f
V
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