apa4838 Anpec Electronics Corporation, apa4838 Datasheet - Page 20

• 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.)
Effective Bypass Capacitor, Cbypass (Cont.)
The bypass capacitor is fed from a 125k
inside the amplifier. Bypass capacitor, Cbypass, val-
ues of 3.3 F to 10 F ceramic or tantalum low-ESR
capacitors are recommended for the best THD and
noise performance.
The bypass capacitance also effects to the start up
time. It is determined in the following equation:
Output Coupling Capacitor, Cc
In the typical single-supply (SE) configuration, an
output coupling capacitor (Cc) is required to block
the DC bias at the output of the amplifier thus pre-
venting 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 gov-
erned by equation.
For example, a 330 F capacitor with an 8 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
low frequencies into the load.
Copyright
Rev. A.1 - Apr., 2003
F
Tstart up = 5 x (Cbypass x 125k )
C
(highpass)=
ANPEC Electronics Corp.
2 R
1
L
C
C
C
are required to pass
resistor
(7)
(6)
20
Power Supply Decoupling, Cs
The APA4838 is a high-performance CMOS audio
amplifier that requires adequate power supply
decoupling to ensure the output total harmonic dis-
tortion (THD) is as low as possible. Power supply
decoupling also prevents the oscillations causing by
long lead length between the amplifier and the
speaker. The optimum decoupling is achieved by
using two different type capacitors that target on dif-
ferent type 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 0.1 F placed as
close as possible to the device V
For filtering lower-frequency noise signals, a large
aluminum electrolytic capacitor of 10 F or greater
p l a c e d n e a r t h e a u d i o p o w e r a m p l i f i e r i s
recommended.
Optimizing Depop Circuitry
Circuitry has been included in the APA4838 to mini-
mize the amount of popping noise at power-up and
when coming out of shutdown mode. Popping oc-
curs whenever a voltage step is applied to the
speaker. In order to eliminate clicks and pops, all
capacitors must be fully discharged before turn-on.
Rapid on/off switching of the device or the shutdown
function will cause the click and pop circuitry. The
value of Ci will also affect turn-on pops. (Refer to
Effective Bypass Capacitance) The bypass voltage
rise up should be slower than input bias voltage.
DD
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lead works best.