APA2068 Anpec Electronics Coropration, APA2068 Datasheet - Page 17

• Manufacturer Part Number: APA2068
• Description: Stereo 2.6W Audio Power Amplifier (with DC_Volume Control)
• Manufacturer: Anpec Electronics Coropration

APA2068
BTL Operation
The APA2068 output stage (power amplifier) has two
pairs of operational amplifiers internally, allowed for
different amplifier configurations.
The power amplifier’ s OP1 gain is setting by internal
unity-gain and input audio signal is come from internal
volume control amplifier, while the second amplifier OP2
is internally fixed in a unity-gain, inverting configuration.
Figure 1 shows that the output of OP1 is connected
to the input to OP2, which results in the output signals
of with both amplifiers with identical in magnitude, but
out of phase 180°. Consequently, the differential gain
for each channel is 2 x (Gain of SE mode).
By driving the load differentially through outputs OUT+
and OUT-, an amplifier configuration commonly referred
to as bridged mode is established. BTL mode operation
is different from the classical single-ended SE amplifier
configuration where one side of its load is connected
to ground.
A BTL amplifier design has a few distinct advantages
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
Copyright
Rev. A.2 - Jul., 2005
Application Descriptions
Volume Control
amplifier output
signal
Figure 1: APA2068 internal configuration
ANPEC Electronics Corp.
(each channel)
Circuit
Vbias
OP1
OP2
OUT+
OUT-
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toa SE amplifier under the same conditions. A BTL
configuration, such as the one used in APA2068, 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
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
33 F to 1000 F) 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:
Output SE/BTL Operation
The ability of the APA2068 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 APA2068, two separate amplifiers drive
OUT+ and OUT- (see Figure 1). The SE/BTL input
controls the operation of the follower amplifier that drives
LOUT- and ROUT-.
the APA2068 is in the BTL mode.
When SE/BTL is held low, the OP2 is turn on and
When SE/BTL is held high, the OP2 is in a high
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