APA2065
Application Descriptions
BTL Operation
Four times the output power same conditions. ABTL
configuration, such as the one used in APA2065, also
createsa second advantage over SE amplifiers. Since
the differential outputs, ROUT+, ROUT-, LOUT+, and
LOUT-, are biased at half-supply, no needDC voltage
exists acrossthe load. This eliminates the need for an
output coupling capacitor which is required in a single
supply, SE configuration.
The APA2065 output stage (power amplifier) has two
pairs of operational amplifiers internally, allowed for
different amplifier configurations.
OUT+
Volume Control
amplifier output
signal
OP1
Single-Ended Operation
RL
OUT-
Consider the single-supply SE configuration shown
Application Circuit. Acoupling capacitor is required to
block the DC offset voltage from reaching the load.
These capacitors can be quite large (approximately
33mF to 1000mF) so they tend tobe 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:
OP2
Vbias
Circuit
Figure 1: APA2065 internal configuration
(each channel)
The power amplifier’s OP1 gain is setting by internal
unity-gain and input audiosignal is comefrom 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).
1
RiCi
1
1
RLCC
(1)
<<
£
Cbypass x 125kW
Output SE/BTL Operation
The ability of the APA2065 to easily switch between
BTL and SE modes is one of its most important costs
savingfeatures.Thisfeatureeliminatestherequirement
for an additional headphone amplifier in applications
whereinternal stereospeakersare driven inBTLmode
but external headphone or speakers must be
accommodated.
Bydrivingthe loaddifferentiallythroughoutputsOUT+
andOUT-,anamplifierconfigurationcommonlyreferred
to asbridged mode isestablished. BTLmodeoperation
isdifferent from the classical single-ended SE amplifier
configuration where one side of its load is connected
Internal to theAPA2065, two separateamplifiersdrive
OUT+ and OUT- (see Figure 1). The SE/BTL input
controlstheoperationofthefolloweramplifierthatdrives
LOUT-andROUT-.
to ground.
A BTL amplifier design has a few distinct advantages
over the SE configuration, as it provides differential
drive to the load, thus doubling the output swing for a
specified supply voltage.
· When SE/BTL is held low, the OP2 is turn on and
the APA2065 is in the BTL mode.
Copyright ã ANPEC Electronics Corp.
15
www.anpec.com.tw
Rev. A.4 - Aug., 2005
ANPEC [ ANPEC ELECTRONICS COROPRATION ]
