MP7722 MPS, MP7722 Datasheet - Page 8

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

The quality factor (Q) of the LC filter is important.
If this is too low output noise will increase, and if
this is too high then peaking may occur at high
signal
flatness. The circuit Q is set by the load
resistance (speaker resistance, typically 4Ω or
8Ω) and is calculated as:
Where ω
radians per second and f
filter with Q between 0.7 and 2.
The actual output ripple and noise is greatly
affected by the type of inductor and capacitor
used in the LC filter. Use a film capacitor and an
inductor with sufficient power handling capability
to supply the output current to the load. The
inductor
characteristics. If the inductor exhibits hard
saturation, it should operate well below the
saturation
Powdered Iron or similar type toroidal cores are
recommended. If open or shielded bobbin ferrite
cores are used for multi-channel designs, make
sure that the start windings of each inductor line
up (all starts going toward SW pin or all starts
going toward the output) to prevent crosstalk or
other channel-to-channel interference.
Output Coupling Capacitors
The output AC coupling capacitors C
C
only the amplified AC signal from the LC filter to
the load. The combination of the coupling
capacitor and the load resistance results in a
first-order high-pass filter. The values of C
and C
required minimum frequency is still allowed to
pass. The output corner frequency (-3dB point),
f
Set the output corner frequency at or below the
minimum required frequency.
The output coupling capacitor carries the full
load current, so the capacitor should be chosen
such that its ripple current rating is greater than
the maximum load current. Low ESR aluminum
electrolytic capacitors are recommended.
MP7722 Rev. 1.3
9/25/2006
OUT
OUT2
, can be calculated as:
serve to block DC voltages and thus pass
OUT2
frequencies
0
f
should
OUT
should be selected such that the
is the characteristic frequency in
current.
Q
=
=
ω
2
0
×
×
π
R
exhibit
L
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
reducing
×
Gapped
=
R
MP7722 – 2 x 20W CLASS D STEREO SINGLE ENDED AUDIO AMPLIFIER
2
LOAD
0
π
1
×
is in Hz. Use a LC
f
0
×
soft
×
C
the
R
OUT
L
ferrite,
saturation
passband
© 2006 MPS. All Rights Reserved.
OUT1
www.MonolithicPower.com
MPP,
OUT1
and
Input Coupling Capacitors
The input coupling capacitors C
used to pass only the AC signal at the input. In
a typical system application, the source input
signal is typically centered around the circuit
ground, while the MP7722 input is at half the
power supply voltage (V
coupling capacitors transmit the AC signal from
the source to the MP7722 while blocking the
DC
capacitors such that the corner frequency (f
less than the passband frequency. The corner
frequency is calculated as:
Power Source
For maximum output power, the amplifier circuit
requires a regulated external power source to
supply the power to the amplifier. A higher
power supply voltage allows more power to be
delivered to a given load resistance. However if
the
maximum
MP7722 may sustain permanent damage. It is
very important to bypass the power supply pins
with 1µF X7R ceramic capacitors.
Power Supply Pumping
It is also very important to bypass the power
supply with a large aluminum electrolytic
capacitor. It is recommended to use a value of
at least 2200µF. This is necessary to prevent
the supply voltage from getting pumped up to a
level that exceeds the absolute maximum
rating. Supply pumping occurs in single-ended
Class D amplifiers, and is caused by rapid
switch transitions where current is pumped
back up into the supply line. The large capacitor
is necessary to absorb this current and prevent
V
DD
from rising too high.
voltage.
power
operating
f
source
IN
Choose
=
2
×
π
×
voltage
voltage
R
1
the
IN
×
DD
C
/2). The input
IN
input
IN1
of
exceeds
and C
24V,
coupling
IN2
IN
are
) is
the
the
8