apa4838 Anpec Electronics Corporation, apa4838 Datasheet - Page 18

• 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.)
Output SE/BTL Operation
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.
the APA4838 is in the BTL mode.
output impedance state, which configures the
APA4838 as SE driver from -Out. I
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.
Figure 2: HP Sense input selection by phonejack
plug
Copyright
Rev. A.1 - Apr., 2003
When HP Sense is held high, the OP2 is in a high
When HP Sense is held low, the OP2 is turn on and
HP sense
100k
ANPEC Electronics Corp.
VDD
1k
Control
DD
Pin
Headphone Jack
is reduced by
Tip
Ring
Sleeve
18
Output SE/BTL Operation (Cont.)
In Figure 2, input HP Sense operates as follows:
When the phonejack plug is inserted, the 1k 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 (C
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 100k and 1k . Resistor 1k 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.
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 >1k
and output coupling capacitor is required when using
these outputs.
A
V
= -
R
Ri
F
with rail-to-rail output
www.anpec.com.tw
(2)
C
)