apa3002 Anpec Electronics Corporation, apa3002 Datasheet - Page 19

• Manufacturer Part Number: apa3002
• Description: 12w Stereo Class-d Audio Power Amplifier
• Manufacturer: Anpec Electronics Corporation

Application Information
Class-D Operation
(OUT+)-(OUT-)
Figure1. APA3002 Output Waveform (Voltage & Current)
The APA3002 modulation scheme is shown in Figure 1,
the outputs OUT+ and OUT- are in phase with each other
when no input signals. When output > 0V, the duty cycle
of OUT+ is greater than 50% and OUT- is less than 50%;
on the contrary, when output <0V, the duty cycle of OUT+
is less than 50% and OUT- is greater than 50%. This
method reduces the switching current across the load
and reduces the I
amplifier’ s efficiency.
This modulation scheme has very short pulses across
the load. This makes the small ripple current and very
little loss on the load, and the LC filter can be eliminated
in most applications. Adding the LC filter can increase the
efficiency by filter the ripple current.
Copyright
Rev. A.6 - Sep., 2009
(OUT+)-(OUT-)
(OUT+)-(OUT-)
APA3002
OUT+
OUT+
OUT+
Output = 0V
Output > 0V
Output < 0V
OUT-
OUT-
OUT-
OUT
OUT
OUT
I
I
I
OUT
OUT
OUT
ANPEC Electronics Corp.
2
R loss in the load that improves the
19
Square Wave Into the Speaker
To apply the square wave into the speaker may cause the
voice coil of speaker jumps out the air gap and defaces the
voice coil. However, this depends on if the amplitude of
square wave is high enough and the bandwidth of speaker
is higher than the square wave’ s frequency. For 250kHz
switching frequency, this is not an issue for the
speaker because the frequency is beyond the audio band,
and can’ t significantly move the voice coil, as cone move-
ment is proportional to 1/f
Input Resistor (R
In order to achieve the 32 steps gain setting, the R
the input resistance network (R
input resistor’ s range from the smallest to the maximum
is about 15 times, therefore, the input high-pass filter’ s
low cutoff frequency will change 15 times from low to
high. The cutoff frequency can be calculated by equation
1.
In the typical application, an input capacitor, C
to allow the amplifier to bias the input signal to the proper
DC level for optimum operation. In this case, C
minimum input impedance R
the corner frequency is determined in the following
equation:
The value of C
it directly affects the low frequency performance of the
circuit. Consider the example, where R
the specification calls for a flat bass response down
to 40Hz. The equation is reconfigured as below:
When the input resistance variation is considered, the C
is 0.40 F, so a value in the range of 0.47 F to 1.0 F
would be chosen. A further consideration for this ca-
pacitor is the leakage path from the input source
through the input network (R
This leakage current creates a DC offset voltage at
the input to the amplifier that reduces useful headroom,
Input Capacitor (C
C
f
C(highpass
i
2
1
R
)
i
f
c
i
2
must be considered carefully because
(2)
i
)
R
1
i
)
i
C
i
(1)
2
for frequency out of audio band.
i
form a high-pass filter with
i
+ R
i
& R
f
, C
www.anpec.com.tw
f
i
) of amplifier. The
) to the load.
i
is 10k
i
, is required
i
and the
i
varies
and
i