APA2069 查看數據表（PDF） - Anpec Electronics
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APA2069 Datasheet PDF : 26 Pages
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APA2069
Application Descriptions (Cont.)
Power Supply Decoupling, Cs
The APA2069 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
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 0.1µF placed as
close as possible to the device V lead works best.
DD
For filtering lower-frequency noise signals, a large
aluminum electrolytic capacitor of 10µF or greater
placed near the audio power amplifier is recommended.
size of Cbypass and the turn-on time. In a SE
configuration, the output coupling capacitor, CC, is of
particular concern.
This capacitor discharges through the internal 10kΩ
resistors. Depending on the size of C , the time
C
constant can be relatively large. To reduce transients
in SE mode, an external 1kΩ resistor can be placed in
parallel with the internal 10kΩ resistor. The tradeoff
for using this resistor is an increase in quiescent current.
In the most cases, choosing a small value of Ci in the
range of 0.33µF to 1µF, Cb being equal to 4.7µF and
an external 1kΩ resistor should be placed in parallel
with the internal 10kΩ resistor 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. So it
is advantageous to use low-gain configurations.
Optimizing Depop Circuitry
Shutdown Function
Circuitry has been included in the APA2069 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.
In order to reduce power consumption while not in use,
the APA2069 contains a shutdown pin to externally
turn off the amplifier bias circuitry. This shutdown
feature turns the amplifier off when a logic low is placed
on the SHUTDOWN pin. The trigger point between a
logic high and logic low level is typically 2.0V. It is
best to switch between ground and the supply VDD to
provide maximum device performance.
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
By switching the SHUTDOWN pin to low, the amplifier
enters a low-current state, IDD<1µA. APA2069 is in
shutdown mode. On normal operating, SHUTDOWN
pin pull to high level to keeping the IC out of the
shutdown mode. The SHUTDOWN pin should be tied
to a definite voltage to av oid unwanted state
changes.
BTL Amplifier Efficiency
An easy-to-use equation to calculate efficiency starts
out as being equal to the ratio of power from the power
Copyright © ANPEC Electronics Corp.
21
Rev. A.1 - Aug., 2005
www.anpec.com.tw
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