apa4838 Anpec Electronics Corporation, apa4838 Datasheet - Page 19

• Manufacturer Part Number: apa4838
• Description: Stereo 2.8w Audio Power Amplifier With Dc Volume Control And Selectable Gain
• Manufacturer: Anpec Electronics Corporation

APA4838
Application Descriptions (Cont.)
Docking Output Signal (Cont.)
Typical values for the output coupling capacitors are
0.33µF to 1.0µF. If polarized coupling capacitors are
used, connect their ’+’ terminals to the respective
output pin.
The Right Dock and Left Dock channel outputs sig-
nal are also used to driving internal volume control
amplifier.
Input Capacitor, Ci
In the typical application an input capacitor, Ci, is re-
quired 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 determined
in the follow equation:
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 100k
specification calls for a flat bass response down to
40Hz. Equation is reconfigured as follow:
Consider to input resistance variation, the Ci is 0.04 F
so one would likely choose a value in the range of
0.1 F to 1.0 F.
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.
Copyright
Rev. A.1 - Apr., 2003
F
Ci=
C
(highpass)=
2 Rif
1
C
ANPEC Electronics Corp.
2 RiCi
1
and the
(4)
(3)
19
Input Capacitor, Ci (Cont.)
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 capaci-
tors are used, the positive side of the capacitor should
face the amplifier input in most applications as the
DC level there is held at V
that the source DC level. Please note that it is impor-
tant to confirm the capacitor polarity in the application.
Effective Bypass Capacitor, Cbypass
As other power amplifiers, proper supply bypassing
is critical for low noise performance and high power
supply rejection.
The capacitors located on the bypass and power
supply pins should be as close to the device as
possible. The effect of a larger half supply bypass
capacitor will improve PSRR due to increased half-
supply stability. Typical application employ a 5V regu-
lator with 1.0 F and a 0.1 F bypass as supply filtering.
This does not eliminate the need for bypassing the
supply nodes of the APA4838. The selection of by-
pass capacitors, especially Cbypass, is thus depen-
dent upon desired PSRR requirements, click and pop
performance.
To avoid start-up pop noise occurred, the bypass
voltage should rise slower than the input bias voltage
and the relationship shown in equation (5) should be
maintained.
Cbypass x 125k
1
<<
RiCi
DD
1
/2, which is likely higher
www.anpec.com.tw
(5)