APA3002 View Datasheet(PDF) - Anpec Electronics
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APA3002 Datasheet PDF : 29 Pages
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APA3002
Application Information (Cont.)
Input Capacitor (Ci) (Cont.)
especially in high gain applications. For this reason, a
low-leakage tantalum or ceramic capacitor is the best
choice. When polarized capacitors are used, the positive
side of the capacitor should face the amplifier input in most
applications because the DC level of the amplifiers’inputs
is held at 2.5VREF. Please note that it is important to
confirm the capacitor polarity in the application.
COSC & ROSC
The Class-D amplifier’s switching frequency is deter-
mined by the component that connected to ROSC (pin)
and COSC (pin). The frequency can be calculated by the
following equation:
fosc
=
6.6
RoscCosc
(3)
BS+ &BS- Capacitor (CBS)
Since the Full-bridge output stages are only using the N-
channel power MOSFET, the high-side MOSFET’s driver
needs bootstrap circuit to turn on the high side power
MOSFET correctly. A 10nF/35V ceramic capacitor is
recommended.
The bootstrap capacitors are like floating power supply
for high side N-channel power MOSFET gate driver. The
bootstrap capacitors hold the gate-to-source voltage high
enough to keep the high-side N-channel power MOSFET
turn-on at high side switching cycle. At the high-side turn-
on cycle, the voltage of bootstrap capacitors will decrease
through the leakage path. The bootstrap voltage can de-
crease below the minimum Vgs that required to keep the
high-side N-channel power MOSFET turn-on, if driving
into heavy clipping with a less than 50Hz sine wave. When
this occurs, the output power MOSFET becomes source-
follower and the output drops from VDD to approximately
Vclamp.
Driving a square wave at low frequencies is not a design
consideration for majority application, so the 10nf boot-
strap capacitor is recommended. If the low frequency is a
concern, please increase the bootstrap capacitor value to
hold the gate voltage for a longer period and the voltage
drop will not occur.
CLAMP Capacitor (C )
CLAMP
These capacitors are regulated the clamp voltage of N-
channel power MOSFET’s gate voltage, ensuring the
maximum gate-to-source voltage of the MOSFET not to
exceed. 1µF/25V capacitors are recommended.
Power Supply Decoupling (Cs)
The APA3002 is a high-performance CMOS audio amplifier
that requires adequate power supply decoupling to en-
sure the output total harmonic distortion (THD+N) is
as low as possible. Power supply decoupling also pre-
vents the oscillations being caused by long lead
length between the amplifier and the speaker.
The optimum decoupling is achieved by using two dif-
ferent types of capacitors that target on different types of
noise on the power supply leads. For higher frequency
transients, spikes, or digital hash on the line, a good low
equivalent-series-resistance (ESR) ceramic capacitor,
typically is 0.1µF which is placed as close as possible
to the device VDD lead to achieve the best performance.
For filtering lower frequency noise signals, a large alu-
minum electrolytic capacitor of 10µF or greater placed near
the audio power amplifier is recommended.
Ferrite Bead Selection
If the traces from the APA3002 to speaker are short, the
ferrite bead filters can reduce the high frequency radiated
to meet the FCC & CE’s requirements.
A ferrite that has very low impedance at low frequencies
and high impedance at high frequencies (above 1 MHz)
is recommended.
Output LC Filter
If the traces from the APA3002 to speaker are short, it
doesn’t require output filter for FCC & CE standard. Fig-
ure 2 is an example for adding the LC filter, it’s recom-
mended for the situation that the trace from amplifier to
speaker is too long, and needed to eliminate the radiated
emission or EMI.
Copyright © ANPEC Electronics Corp.
20
Rev. A.6 - Sep., 2009
www.anpec.com.tw
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