MP7722 MPS, MP7722 Datasheet - Page 7

• Manufacturer Part Number: MP7722
• Description: 2 x 20W Class D Stereo Single Ended Audio Amplifer
• Manufacturer: MPS

APPLICATION INFORMATION
COMPONENT SELECTION
The MP7722 uses a minimum number of
external components to complete a stereo
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 MP7722 amplifier, the gain
resistors should be set such that the maximum
input signal results in an output voltage swing
that reaches the supply limit (clipping). The
maximum output voltage swing at clipping is
approximately ±V
given input signal voltage, where V
peak input voltage, the voltage gain is:
The voltage gain setting results in the peak
output voltage approaching its maximum for the
maximum input signal. There are applications
where it is desirable to allow the amplifier to
overdrive slightly, allowing the THD to increase
at higher power levels (as the output signal
continues to go further into clipping), and so a
higher gain than A
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
V
resistor R
frequencies for CH1 and CH2 are independent
of each other and are a function of their own
associated components. The proper setting of
the “idle frequency” is important for obtaining
optimum performance. If the frequency is set
too high, the result will be more power loss and
high distortion, while setting the idle switching
frequency too low results in more inductor
ripple, causing more output voltage ripple with
increased the output noise.
MP7722 Rev. 1.3
9/25/2006
DD
, the timing capacitor C
FB
. For the MP7722, the idle switching
A
V
(
MAX
DD
V (max)
/2. To achieve clipping for a
)
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
=
is required.
2
MP7722 – 2 x 20W CLASS D STEREO SINGLE ENDED AUDIO AMPLIFIER
×
INT
V
V
DD
IN
and the feedback
(
pk
)
IN(pk)
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is the
The optimum quiescent switching frequency is
approximately 700KHz to 800KHz. Refer to
Table 1 for recommended values.
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 a 10µH inductor and a 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:
The voltage ripple at the output is approximated
by the equation:
Capacitor and Feedback Resistor (see Figure 1)
Table 1—Switching Frequency vs. V
(V/V)
Gain
17.4
11.9
17.4
33.0
3.9
8.2
8.3
5.6
8.2
Gain
(dB)
30.4
15.0
18.3
21.5
24.8
15.0
18.3
21.5
24.8
V
(kΩ)
330
R
RIPPLE
39
82
39
82
56
82
56
82
FB
f
0
(kΩ)
=
≅
R
4.7
4.7
4.7
4.7
10
10
10
10
10
IN
2
V
π
DD
1
LC
6.8nF
3.3nF
6.8nF
3.3nF
8.2nF
5.6nF
8.2nF
5.6nF
1.8nF
×
C
⎛
⎜
⎜
⎝
INT
f
SW
f
0
⎞
⎟
⎟
⎠
660KHz
660KHz
660KHz
660KHz
670KHz
720KHz
670KHz
720KHz
700KHz
F
DD
SW
, Timing
V
(V)
12
12
12
12
24
24
24
24
24
DD
7