APA4838RI Ver la hoja de datos (PDF) - Anpec Electronics

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APA4838RI

Stereo 2.8W Audio Power Amplifier with DC Volume Control and Selectable Gain

Anpec Electronics 

APA4838

Application Descriptions (Cont.)

Optimizing Depop Circuitry (Cont.)

Shutdown and Mute Function (Cont.)

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,

CC, is of particular concern. This capacitor discharges

through the internal 10kΩ resistors. Depending on

the size of CC, the time constant can be relatively

large. To reduce transients in SE mode, an external

1kΩ resistor can be placed in parallel with the inter-

nal 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, Cbypass being equal to 4.

7µF and an external 1kΩ resistor should be placed in

parallel with the internal 10kΩ resistor should pro-

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.

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 VDD to provide maxi-

mum device performance.

By switching the Shutdown pin to high level, the am-

plifier enters a low-current state, IDD<1µA. APA4838

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 VDD is applied to the Mute pin. Even while

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 VDD or

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 , the PCBEEP mode is active.

DD

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 200kΩ devices

in Application Circuit. Use higher value resistors to

reduce the gain applied to the beep signal.

Copyright  ANPEC Electronics Corp.

21

Rev. A.1 - Apr., 2003

www.anpec.com.tw

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