APA2068 Anpec Electronics Coropration, APA2068 Datasheet - Page 20

• Manufacturer Part Number: APA2068
• Description: Stereo 2.6W Audio Power Amplifier (with DC_Volume Control)
• Manufacturer: Anpec Electronics Coropration

APA2068
Effective Bypass Capacitor, Cbypass (Cont.)
maintained.
The bypass capacitor is fed thru from a 125k resistor
inside the amplifier and the 100k is maximum input
resistance of (Ri+ Rf). Bypass capacitor, Cb, values 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 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 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
frequencies into the load.
Power Supply Decoupling, Cs
The APA2068 is a high-performance CMOS audio
amplifier that requires adequate power supply
decoupling to ensure the output total harmonic
distortion (THD) is as low as possible. Power supply
decoupling also prevents the oscillations causing by
Copyright
Rev. A.2 - Jul., 2005
Application Descriptions (Cont.)
F
Cbypass x 125k
Tstart up = 5 x (Cbypass x 125K )
C
(highpass)=
ANPEC Electronics Corp.
1
2 R
1
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C
C
100k x Ci
C
are required to pass low
1
(8)
(6)
(7)
20
long lead length between the amplifier and the speaker.
The optimum decoupling is achieved by using two
different type capacitors that target on different 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
placed near the audio power amplifier is recommended.
Optimizing Depop Circuitry
Circuitry has been included in the APA2068 to minimize
the amount of popping noise at power-up and when
coming out of shutdown mode. Popping occurs
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
ramp up should be slower than input bias voltage.
Although the bypass pin current source cannot be
modified, the size of Cbypass can be changed to alter
the device turn-on time and the amount of clicks and
pops. By increasing the value of Cbypass, turn-on pop
can be reduced. However, the tradeoff for using a larger
bypass capacitor is to increase the turn-on time for
this device. There is a linear relationship between the
size of Cbypass and the turn-on time. In a SE
configuration, the output coupling capacitor, C
particular concern.
This capacitor discharges through the internal 10k
resistors. Depending on the size of C
DD
www.anpec.com.tw
lead works best.
C
, the time
C
, is of