APA2069 Datasheet, PDF (18/26 Pages) Anpec Electronics Coropration – Stereo 2.6W Audio Power Amplifier (with DC_Volume Control)

APA2069
Application Descriptions (Cont.)
BTL Operation (Cont.)
over the SE configuration, as it provides differentialdrive
to the load, thus doubling the output swing for
aspecified supply voltage.
Four times the output power is possible as compared
toa SE amplifier under the same conditions. A BTL
configuration, such as the one used in APA2069, also
creates a second advantage over SE amplifiers. Since
the differential outputs, ROUT+, ROUT-, LOUT+, and
LOUT-, are biased at half-supply, no need DC voltage
exists across the load. This eliminates the need for an
output coupling capacitor which is required in a single
supply, SE configuration.
Single-Ended Operation
controls the operation of the follower amplifier that drives
LOUT- and ROUT-.
• When SE/BTL is held low, the OP2 is turn on and
the APA2069 is in the BTL mode.
• When SE/BTL is held high, the OP2 is in a high
output impedance state, which configures the
APA2069 as SE driver from OUT+. I_DD is reduced by
approximately one-half in SE mode.
Control of the SE/BTL input can be a logic-level TTL
source or a resistor divider network or the stereo
headphone jack with switch pin as shown in Application
Circuit.
Consider the single-supply SE configuration shown
Application Circuit. A coupling capacitor is required to
block the DC offset voltage from reaching the load.
These capacitors can be quite large (approximately
33µF to 1000µF) so they tend to be expensive, occupy
valuable PCB area, and have the additional drawback
of limiting low-frequency performance of the system
(refer to the Output Coupling Capacitor).The rules
described still hold with the addition of the following
relationship:
1
Cbypass x 125kΩ
≤
1
RiCi
<<
1
RLCC
(1)
Output SE/BTL Operation
The ability of the APA2069 to easily switch between
BTL and SE modes is one of its most important costs
saving features. This feature eliminates the requirement
for an additional headphone amplifier in applications
where internal stereo speakers are driven in BTL mode
but external headphone or speakers must be
accommodated.
Internal to the APA2069, two separate amplifiers drive
OUT+ and OUT- (see Figure 1). The SE/BTL input
VDD
100kΩ
SE/BTL
1kΩ
Control
Pin
Ring
Sleeve
Tip
Headphone Jack
Figure 2: SE/BTL input selection by phonejack plug
In Figure 2, input SE/BTL operates as follows :
When the phonejack plug is inserted, the 1kΩ resistor
is disconnected and the SE/BTL input is pulled high
and enables the SE mode. When the input goes high,
the OUT- amplifier is shutdown causing the speaker to
mute. The OUT+ amplifier then drives through the
output capacitor (C_O) into the headphone jack. When
there is no headphone plugged into the system, the
contact pin of the headphone jack is connnected from
the signal pin, the voltage divider set up by resistors
100kΩ and 1kΩ.Resistor 1kΩ then pulls low the
SE/BTL pin, enabling the BTL function.
Copyright © ANPEC Electronics Corp.
18
Rev. A.1 - Aug., 2005
www.anpec.com.tw