APA0710/0711
Application Descriptions
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.
BTL Operation
V o+
Single-Ended Operation
O P 1
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).
R L
Vo-
Vbias
O P 2
Figure1:
APA0710/1 power amplifier internal configuration
The power amplifier OP1 gain is setting by external
gain setting, while the second amplifier OP2 is
internally fixedinaunity-gain,invertingconfiguration.
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 2X (Gain of SE
mode).
The rules described still hold with the addition of the
following relationship :
1
1
1
£
<<
(1)
Cbypass´ 80kO (RI +RF)´ CI
RLCC
Output SE/BTL Operation (for APA0710 only)
The ability of the APA0710 to easily switch between
BTL and SE modes is one of its most important costs
savingfeatures.Thisfeatureeliminatestherequirement
for an additional headphone amplifier in applications
where internal speakers are driven in BTL mode but
By driving the load differentially through outputs Vo+
andVo-, an amplifier configuration commonly referred
to asbridged mode isestablished. BTLmodeoperation
isdifferent from the classical single-ended SE amplifier
configuration where one side of its load is connected
to ground.
externalheadphoneorspeakersmustbeaccommodated.
Internal to theAPA0710, two separateamplifiersdrive
Vo+ and Vo- (see Figure 2). The SE/BTLinput controls
the operation of the follower amplifier that drivesVo-.
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 APA0710 is in the BTL mode.
· When SE/BTL is held high, the OP2 is in a high
output impedance state, which configures the
APA0710 as SE driver from Vo+. IDD is reduced by
Four times the output power is possible as compared
to a SE amplifier under the same conditions. A BTL
configuration, such as the one used in APA0710, also
createsa second advantage over SE amplifiers. Since
the differential outputs, Vo+, Vo- are biased at half-
approximately one-half in SE mode.
Control of the SE/BTL input can be a logic-level TTL
Copyright ã ANPEC Electronics Corp.
Rev. A.5 - Oct., 2005
20
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ANPEC [ ANPEC ELECTRONICS COROPRATION ]
