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APA2177 Datasheet(PDF) 14 Page - Anpec Electronics Coropration

No. de Pieza. APA2177
Descripción  25mW Stereo Cap-Free Headphone Driver
Descarga  22 Pages
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Fabricante  ANPEC [Anpec Electronics Coropration]
Página de inicio  http://www.anpec.com.tw
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APA2177 Datasheet(HTML) 14 Page - Anpec Electronics Coropration

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Copyright
© ANPEC Electronics Corp.
Rev. A.3 - Nov., 2017
APA2177
www.anpec.com.tw
14
Application Information
Input Capacitor, C
i
In the typical application, an input capacitor, C
i, is required
to allow the amplifier to bias the input signal to the proper
DC level for optimum operation. In this case, C
i and the
minimum input impedance Ri from a high-pass filter with
the corner frequency are determined in the following
equation:
The value of C
i is important to consider as it directly af-
fects the low frequency performance of the circuit. Ri is
the internal input resistance that typical value is 13.2K
at 6dB and the specification calls for a flat bass response
down to 20Hz. Equation is reconfigured as below:
Power Supply Decoupling (C
s)
The APA2177 is a high-performance CMOS audio ampli-
fier that requires adequate power supply decoupling to
ensure the output total harmonic distortion (THD+N) is
as low as possible. Power supply decoupling also pre-
vents the oscillations causing by long lead length be-
tween the amplifier and the speaker.
Charge pump flying capacitor, C
CPF
The flying capacitor affects the load transient of the charge
pump. If the capacitor
’s value is too small, then that will
degrade the charge pump
’s current driver capability and
the performance of headphone drive amplifier.
Increasing the flying capacitor
’s value will improve the
load transient of charge pump. It is recommend using
t h e l o w ES R c e r a m ic c a p a c i to r s ( X7 R t y pe is
recommended) above 1
µF.
(1)
Ci
i
)
C(highpass
f
R
2
1
f
π
=
Consider to input resistance variation, the C
i is 0.6µF so
one would likely choose a value in the range of 0.6
µF to
1
µF. A further consideration for this capacitor is the leak-
age path from the input source through the input network
(R
i + Rf, Ci) to the load.
This leakage current creates a DC offset voltage at the
input to the amplifier that reduces useful headroom, es-
pecially in high gain applications. For this reason, a low
leakage tantalum or ceramic capacitor is the best choice.
When polarized capacitors are used, the negative side of
the capacitor should face the amplifier input in most ap-
plications as the DC level there is held at GND, which is
likely lower than the source DC level. Please note that it
is important to confirm the capacitor polarity in the
application.
C
i
i
f
R
2
1
C
π
=
(2)
The optimum decoupling is achieved by using two differ-
ent types of capacitor that target 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 0.1
µF, is placed as close as possible to the de-
vice VDD lead for the best performance. For filtering lower
frequency noise signals, a large aluminum electrolytic
capacitor of 1
µF or greater placed near the audio power
amplifier is recommended.
Charge pump output capacitor, C
CPO
The output capacitor
’s value affects the power ripple di-
rectly at HPVSS. Increasing the value of output capacitor
reduce the power ripple. The ESR of output capacitor
affects the load transient of HPVSS. Lower ESR and
greater than 1
µF ceramic capacitor is recommendation.


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