APA4838 Ver la hoja de datos (PDF) - Anpec Electronics

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Fabricante

APA4838

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

Anpec Electronics 

APA4838

Application Descriptions (Cont.)

Output SE/BTL Operation

Output SE/BTL Operation (Cont.)

The ability of the APA4838 to easily switch between

BTL and SE modes is one of its most important costs

saving features. This feature eliminates the require-

ment for an additional headphone amplifier in appli-

cations where internal stereo speakers are driven in

BTL mode but external headphone or speakers must

be accommodated.

Internal to the APA4838, two separate amplifiers drive

–Out and +Out for each channel (see Figure 1). The

HP Sense input controls the operation of the follower

amplifier that drives +Left Out and +Right Out.

• When HP Sense is held low, the OP2 is turn on and

the APA4838 is in the BTL mode.

•When HP Sense is held high, the OP2 is in a high

output impedance state, which configures the

APA4838 as SE driver from -Out. I is reduced by

DD

approximately one-half in SE mode.

Control of the HP Sense input can be a logic-level

TTL source or a resistor divider network or the ste-

reo headphone jack with switch pin as shown in Ap-

plication Circuit.

In Figure 2, input HP Sense operates as follows:

When the phonejack plug is inserted, the 1kΩ resis-

tor is disconnected and the HP Sense input is pulled

high and enables the SE mode.

When this input goes high level, the +Out amplifier is

shutdown causing the speaker to mute. The -Out

amplifier then drives through the output capacitor (CC)

into the headphone jack.

When there is no headphone plugged into the system,

the contact pin of the headphone jack is connected

from the signal pin, the voltage divider set up by re-

sistors 100kΩ and 1kΩ. Resistor 1kΩ then pulls low

the HP Sense pin, enabling the BTL function.

Docking Output Signal

APA4835 internal first amplifier is used as audio sig-

nal pre-amplfier and feedback resistor is connected

between Dock output pin and audio input pin.

However, the internal first amplifier’s closed-loop gain

can be adjusted using external resistors. Use Equa-

tion 2 to determine the input and feedback resistor

values for a desired gain.

VDD

100kΩ

HP sense

1kΩ

Control

Pin

Ring

Sleeve

Tip

Headphone Jack

Figure 2: HP Sense input selection by phonejack

plug

AV

=

-

RF

Ri

(2)

The Dock output signal provides low distortion audio

quality for light driving output. ex. active speaker,

monitors or audio/visual equipment. These two out-

puts can driving load of >1kΩ with rail-to-rail output

and output coupling capacitor is required when using

these outputs.

Copyright  ANPEC Electronics Corp.

18

Rev. A.1 - Apr., 2003

www.anpec.com.tw

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