APA4801JI-TR ANPEC [Anpec Electronics Coropration], APA4801JI-TR Datasheet - Page 10

• Manufacturer Part Number: APA4801JI-TR
• Description: Stereo 280mW 8 OHM Speaker Driver with Mute
• Manufacturer: ANPEC [Anpec Electronics Coropration]

APA4801
Application Note
Input Capacitor, Ci
In the typical application an input capacitor , Ci , is
required to allow the amplifier to bias the input signal
to the proper DC level for optimum operation . In this
case , the external capacitor Ci and the internal re-
sistance Ri form a high-pass filter with the corner fre-
quency 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 APA4801 where Ri is 130k
fixed . Equation is reconfigured as follow :
And the ceramic capacitor is recommanded
Bias Capacitor, Cb
As with any power amplifier , proper supply bypass-
ing is critical for low noise performance and high
power supply rejection . 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 bias capacitor is improved PSRR due to
increased half-supply stability . Typical applications
employ a 5V regulator with 10 F and a 0.1 F bias
capacitors which aid in supply filtering . This does
not eliminate the need for bypassing the supply nodes
of the APA4801 . The selection of bias capacitors ,
especially Cb , is thus dependent upon desired PSRR
requirements , click and pop performance . The ca-
pacitor is fed from a 50k source inside the amplifier.
To keep the start-up pop as low as possible , the
relationship shown in equation should be maintained.
As an example , consider a circuit where Cb is
4.
values into the equation we get 4.26 7.69 which
satisfies the rule . Bias capacitor , Cb , values of
2.2 F to 10 F ceramic or tantalum low-ESR capaci-
tors are recommended for the best THD and noise
performance.
Copyright
Rev. A.5 - Apr., 2001
F , Ci is 1 F and Ri is 130k
fc (highpass)= 1/ (2 RiCi)
Ci= 1/(2 *130k *fc)
1/(Cb*50k ) 1/{Ci*Ri}
ANPEC Electronics Corp.
. Inserting these
internal
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10
Output Coupling Capacitor, Cc
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 .
For example , a 220 F capacitor with an 32 speaker
would attenuate low frequencies below 22Hz . 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 Cc are required to pass
low frequencies into the load .
Optimizing Depop Circuitry
When the amplifier is in mute mode , both of the out-
put stage and input bypass continues to be biased .
And no pop noise will be heard during the transition
out of mute mode .
Power Supply Decoupling , Cs
APA4801 is a high-performance CMOS audio ampli-
fier 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 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 tran-
sients , spikes , or digital hash on the line , a good
low equivalent-series-resistance (ESR) ceramic ca-
pacitor , typically 0.1 F placed as close as possible
to the device V
frequency noise signals , a large aluminum electro-
lytic capacitor of 10 F or greater placed near the audio
power amplifier is recommended .
fc(highpass)= 1/(2 R
DD
lead works best . For filtering lower-
L
Cc)
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