APA3002 View Datasheet(PDF) - Anpec Electronics
Part Name
Description
Manufacturer
APA3002 Datasheet PDF : 29 Pages
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APA3002
Application Information
Class-D Operation
Output = 0V
OUT+
OUT-
OUT
(OUT+)-(OUT-)
IOUT
Output > 0V
OUT+
OUT-
OUT
(OUT+)-(OUT-)
IOUT
Output < 0V
OUT+
OUT-
(OUT+)-(OUT-)
OUT
IOUT
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 I2R loss in the load that improves the
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.
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/f2 for frequency out of audio band.
Input Resistor (Ri)
In order to achieve the 32 steps gain setting, the Ri varies
the input resistance network (Ri & Rf) of amplifier. The
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.
Input Capacitor (Ci)
In the typical application, an input capacitor, C , is required
i
to allow the amplifier to bias the input signal to the proper
DC level for optimum operation. In this case, Ci and the
minimum input impedance Ri form a high-pass filter with
the corner frequency is determined in the following
equation:
fC(highpass)
=
1
2πRiCi
(1)
The value of Ci must be considered carefully because
it directly affects the low frequency performance of the
circuit. Consider the example, where Ri is 10kΩ and
the specification calls for a flat bass response down
to 40Hz. The equation is reconfigured as below:
Ci
=
1
2πRifc
(2)
When the input resistance variation is considered, the C
i
is 0.40µF, so a value in the range of 0.47µF to 1.0µF
would be chosen. A further consideration for this ca-
pacitor is the leakage path from the input source
through the input network (Ri + Rf, Ci) to the load.
This leakage current creates a DC offset voltage at
the input to the amplifier that reduces useful headroom,
Copyright © ANPEC Electronics Corp.
19
Rev. A.6 - Sep., 2009
www.anpec.com.tw
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