APA2030/2031
Application Descriptions
To avoid start-up pop noise occurred, the bypass volt-
age should be rise slower then the input bias voltage
and the relationship shown in equation should be
maintained.
1
fC (highpass)=
(2)
2πRimin×Ci
The value of Ci is important to consider as it directly
affects the low frequency performance of the circuit.
Consider the example where Ri is 90kΩ when 6dB
gain is setting and the specification calls for a flat
bass response down to 40Hz . Equation is reconfigured
as follow:
1
1
(4)
<<
Cbypass ×125kȍ
Ci×180kȍ
The capacitor is fed from a 125kΩ source inside the
amplifier. Bypass capacitor, Cb, values of 3.3µF to
10µF ceramic or tantalum low-ESR capacitors are
recommendedforthebestTHDandnoiseperformance.
1
Ci=
(3)
2πRifc
Consider to input resistance variation, the Ci is 0.04µF
so one would likely choose a value in the range of
0.1µF to 1.0µF.
The bypass capacitance also effect to the start up
time. It is determined in the follow equation:
Tstart up =5x(Cbypassx125kΩ)
(5)
A further consideration for this capacitor is the leak-
age path from the input source through the input net-
work (Ri+Rf, Ci) to the load. This leakage current
creates a DC offset voltage at the input to the ampli-
fier that reduces useful headroom, especially in high
gain applications. For this reason a low-leakage tan-
talum 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 as the DC level there is held at VDD/2,
which is likely higher that the source DC level. Please
note that it is important to confirm the capacitor po-
larity in the application.
Output Coupling Capacitor, Cc (for APA2030
only)
In the typical single-supply SE configuration, an out-
put coupling capacitor (Cc) is required to block the
DC bias at the output of the amplifier thus preventing
DC currents in the load. As with the input coupling
capacitor, the output coupling capacitor and imped-
ance of the load form a high-pass filter governed by
equation.
1
fc(highpass)=
(6)
Effective Bypass Capacitor, Cbypass
π
L
C
2 R C
As with any power amplifier, proper supply bypass-
ing is critical for low noise performance and high
power supply rejection.
For example, a 330µF capacitor with an 8Ω speaker
would attenuate low frequencies below 60.6Hz. The
main disadvantage, from a performance standpoint,
is the load impedance is typically small, which drives
the low-frequency corner higher degrading the bass
response. Large values of C are required to pass
low frequencies into the load.C
The capacitor location on both the bypass and power
supply pins should be as close to the device as
possible. The effect of a larger half supply bypass
capacitor is improved PSRR due to increased half-
supply stability. Typical applications employ a 5V regu-
lator with 1.0µF and a 0.1µF bypass capacitors which Power Supply Decoupling, Cs
aid in supply filtering. This does not eliminate the need
The APA2030/1 is a high-performance CMOS audio
for bypassing the supply nodes of the APA2030/1.
The selection of bypass capacitors, especially Cb, is
thus dependent upon desired PSRR requirements,
click and pop performance.
amplifier that requires adequate power supply
decoupling to ensure the output total harmonic distor-
tion (THD) is as low as possible.
Copyright ANPEC Electronics Corp.
20
www.anpec.com.tw
Rev. A.2 - Apr., 2004
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
