APA0713 Ver la hoja de datos (PDF) - Anpec Electronics
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APA0713 Datasheet PDF : 19 Pages
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APA0713
Application Information (Cont.)
Effective Bypass Capacitor, Cbypass (Cont.)
PSRR due to increased half-supply stability. Typical ap-
plication employs a 5V regulator with 1.0µF and a 0.1µF
bypass as supply filtering. This does not eliminate the
need for bypassing the supply nodes of the APA0713.
The selection of bypass capacitors, especially Cbypass, thus
depends upon desired PSRR requirements, click- and-
pop performance.
To avoid start-up pop noise occurred, the bypass volt-
age should rise slower than the input bias voltage and
the relationship shown in equation (4) should be
maintained.
1
<<
1
(3)
Cbypass × 80KΩ
(RI + RF)× CI
The bypass capacitor is fed from a 80KΩ resistor inside
the amplifier. Bypass capacitor, Cbypass, values of 0.1µF
to 2.2µF ceramic or tantalum low-ESR capacitors
are recommended for the best THD+N and noise
performance.
The bypass capacitance also effects to the start up time. It
is determined in the following equation :
Tstartup = 5 × (Cbypass × 80KΩ)
(4)
Power Supply Decoupling, CS
The APA0713 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. The optimum
decoupling is achieved by using two different types of
capacitors 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 0.1µF,
is placed as close as possible to the device’s VDD lead,
which is for the best performance. For filtering lower-fre-
quency noise signals, a large aluminum electrolytic ca-
pacitor of 10µF or greater placed near the audio power
amplifier is recommended.
Optimizing Depop Circuitry
Circuitry has been included in the APA0713 to mini-
mize the amount of popping noise at power-up and when
coming out of shutdown mode. Popping occurs when-
ever a voltage step is applied to the speaker. In order to
eliminate click-and-pop, all capacitors must be fully dis-
charged before turn-on. Rapid on/off switching of the de-
vice or the shutdown function will cause the click-and-
pop circuitry. The value of C will also affect turn-on pops
I
(refer to Effective Bypass Capacitance). The bypass volt-
age rise up should be slower than input bias voltage.
Although the bypass pin current source cannot be
modified, the size of C can be changed to alter the
bypass
device turn-on time and the amount of click-and-pop. 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 C and the turn-
bypass
on time.
In the most cases, choosing a small value of CI in the
range
of
0.33µF
to
1µF,
C
bypass
being
equal
to
1µF
should
produce a virtually clickless and popless turn-on.
A high gain amplifier intensifies the problem as the small
delta in voltage is multiplied by the gain. Hence, it is ad-
vantageous to use low-gain configurations.
Shutdown Function
In order to reduce power consumption while not in using,
the APA0713 contains a shutdown function to externally
turn off the amplifier bias circuitry. This shutdown feature
turns the amplifier off when a logic low on the Shutdown
pin for APA0713.
The trigger point between a logic high and logic low level
is typically 0.4VDD. It’s better to switch between ground
and the supply voltage VDD to provide maximum device
performance.
By switching the Shutdown pin to high level, the amplifier
enters a low-current state, I for APA0713. APA0713 is
DD
in shutdown mode. In normal operation, APA0713’s
Shutdown pin should be pulled to low level to keep the IC
Copyright © ANPEC Electronics Corp.
11
Rev. A.2 - Apr., 2012
www.anpec.com.tw
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