apa4838 Anpec Electronics Corporation, apa4838 Datasheet - Page 21

• Manufacturer Part Number: apa4838
• Description: Stereo 2.8w Audio Power Amplifier With Dc Volume Control And Selectable Gain
• Manufacturer: Anpec Electronics Corporation

APA4838
Application Descriptions (Cont.)
Optimizing Depop Circuitry
Although the bypass pin current source cannot be
modified, the size of Cbypass can be changed to al-
ter 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
through the internal 10k
the size of C
large. To reduce transients in SE mode, an external
1k resistor can be placed in parallel with the inter-
nal 10k 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 0.33 F to 1 F, Cbypass being equal to 4.
7 F and an external 1k resistor should be placed in
parallel with the internal 10k
duce 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.
Shutdown and Mute Function
In order to reduce power consumption while not in
use, the APA4838 contains a Shutdown pin to exter-
nally turn off the amplifier bias circuitry. This shut-
down feature turns the amplifier off when a logic high
is placed on the Shutdown pin.
Copyright
Rev. A.1 - Apr., 2003
C
, is of particular concern. This capacitor discharges
ANPEC Electronics Corp.
C
, the time constant can be relatively
resistors. Depending on
(Cont.)
resistor should pro-
21
Shutdown and Mute Function (Cont.)
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 voltage V
mum device performance.
By switching the Shutdown pin to high level, the am-
plifier enters a low-current state, I
is in shutdown mode. On normal operating, Shut-
down pin pull to low level to keeping the IC out of the
shutdown mode. The Shutdown pin should be tied
to a definite voltage to avoid unwanted state changes.
The APA4838 mutes the amplifier and DOCK out-
puts when V
muted, the APA4838 will amplify a system alert (beep)
signal whose magnitude satisfies the PCBEEP de-
tect circuitry. Applying 0V to the Mute pin returns the
APA4838 to normal operation. Prevent unanticipated
mute behavior by connecting the Mute pin to V
ground. Do not let the Mute pin float.
PCBEEP Detect Circuitry
APA4838 integrates a PCBEEP detect circuit for note-
book and computer used. When Beep In signal is
greater than 1/2V
APA4838 will force to BTL mode and the internal fixed
gain mode. The Beep In signal becomes the ampli-
fier input signal and plays on the system speaker with-
out coupling capacitor. Use input resistor between
stereo input pin and Beep In to attenuate Beep In
signal. These resistors are shown as 200k devices
in Application Circuit. Use higher value resistors to
reduce the gain applied to the beep signal.
DD
is applied to the Mute pin. Even while
DD
, the PCBEEP mode is active.
DD
DD
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to provide maxi-
<1 A. APA4838
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