APA2030_13 Datasheet, PDF (18/30 Pages) Anpec Electronics Coropration – Stereo 2.6W Audio Amplifier (With Gain Control)

APA2030/2031
Application Information (Cont.)
Input Capacitor, C_i (Cont.)
A further consideration for this capacitor is the leakage
path from the input source through the input network
(R_i+R_f, C_i) to the load. This leakage current creates a DC
offset voltage at the input to the amplifier that reduces
useful headroom, especially in high gain applications.
For this reason, a low-leakage tantalum or ceramic ca-
pacitor is the best choice. When polarized capacitors are
used, the positive side of the capacitor should face the
amplifiers’ input in most applications becasue the DC
level of the amplifiers’inputs is held at V_DD/2. Please note
that it is important to confirm the capacitor polarity in the
application.
Effective Bypass Capacitor, C_bypass
As to any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection.
The capacitor located on both the bypass and power sup-
ply pins should be as close to the device as possible.
The effect of a larger half supply bypass capacitor im-
proves PSRR due to increased half-supply stability. Typi-
cal applications employ a 5V regulator with 1.0µF and a
0.1µF bypass capacitors which aid in supply filtering. This
does not eliminate the need for bypassing the supply
nodes of the APA2030/1. The selection of bypass
capacitors, especially C , is thus dependent upon de-
B
sired PSRR requirements, click and pop performance.
To avoid the start-up pop noise occurred, the bypass volt-
age should rise slower than the input bias voltage and
the relationship shown in equation should be maintained.
1
<<
1 _{........................(4)}
Cbypass× 250kΩ Ci ×180kΩ
The capacitor is fed from a 250kΩ source inside the
amplifier.
Bypass
capacitor,
C,
B
values
of
3.3µF
to
10µF
ceramic or tantalum low-ESR capacitors are recom-
mended for the best THD+N and noise performance.
The bypass capacitance also affects the start-up time. It
is determined in the following equation:
TStartup = 5 × (Cbypass × 250kΩ)...........................(5)
Output Coupling Capacitor, C_c (for APA2030 only)
In the typical single-supply SE configuration, an output
coupling capacitor (C ) is required to block the DC bias at
c
the output of the amplifier thus preventing DC currents in
the load. As with the input coupling capacitor, the output
coupling capacitor and impedance of the load form a high-
pass filter governed by the following equation.
fc(highpass ) = ¹ ...........................................(6)
2πRLCc
For example, a 330µF capacitor with an 8Ω speaker
would attenuate low frequencies below 60.6Hz. Large
values of C_C are required to pass low frequencies into
the load.
Power Supply Decoupling, C
S
The APA2030/1 is a high-performance CMOS audio am-
plifier that requires adequate power supply decoupling
to ensure the output total harmonic distortion (THD+N) is
as low as possible.
Power supply decoupling also prevents the oscillations
being caused by long lead length between the amplifier
and the speaker.
The optimum decoupling is achieved by using two differ-
ent types of capacitors that targets 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 0.1µF placed as close as possible to the device
VDD lead works best. For filtering lower-frequency noise
signals, a large aluminum electrolytic capacitor of 10µF
or greater placed near the audio power amplifier is
recommended.
Shutdown Function
In order to reduce power consumption when not in use,
the APA2030/1 contains a shutdown pin to externally
turn off the amplifier bias circuitry. This shutdown feature
turns the amplifier off when a logic low is placed on the
SHUTDOWN pin. The trigger point between a logic high
and logic low level is typically 2.0V. It is better to switch
between the ground and the supply V to provide maxi-
DD
mum device performance.
Copyright © ANPEC Electronics Corp.
18
Rev. A.10 - Aug., 2013
www.anpec.com.tw