apa0712 Anpec Electronics Corporation, apa0712 Datasheet - Page 13

• Manufacturer Part Number: apa0712
• Description: 1.4w Mono Audio Low-voltage Audio Power Amplifier
• Manufacturer: Anpec Electronics Corporation

Application Descriptions
Figure1: APA0712 power amplifier internal configuration
The power amplifier OP1 gain is set by external gain
setting, while the second amplifier OP2 is inter-
nally fixed in a unity-gain, inverting configuration. Fig-
ure 1 shows that the output of OP1 is connected to
the input to OP2, which results in the output sig-
nals 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).
By driving the load differentially through outputs V
and V
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 differential
drive to the load, thus doubling the output swing for a
specified supply voltage. 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 APA0712,
also creates a second advantage over SE amplifiers.
Since the differential outputs, V
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.
BTL Operation
Copyright
Rev. A.2 - Aug., 2007
APA0712
INPUT
ON,
an amplifier configuration commonly referred
ANPEC Electronics Corp.
R
i
V
bias
R
-
+
OP1
f
-
+
OP2
OP
, V
ON
BTL_CONFIG
V
V
are biased at
ON
OP
OP
13
Input Resistance, R
The gain of the APA0712 is set by the external resis-
tors (R
BTL mode operation brings the factor of 2 in the gain
equation due to the inverting amplifier mirroring the
voltage swing across the load. The input resistance
will affect the low frequency performance of audio
signal.
Input Capacitor, C
In the typical application an input capacitor, C
required to allow the amplifier to bias the input signal
to the proper DC level for optimum operation. In this
case, C
high-pass filter with the corner frequency determined
in the follow equation:
The value of C
affects the low frequency performance of the circuit.
Consider the example where R
specification calls for a flat bass response down to
40Hz. Equation is reconfigured as follow:
Consider to input resistance variation, the C
so one would likely choose a value in the range of 0.22 F
to 1.0 F.A further consideration for this capacitor is the
leakage path from the input source through the input
network (R
This leakage current creates a DC offset voltage at the
input to the amplifier that reduces useful headroom,
especially in high gain applications. For this reason a
low-leakage tantalum or ceramic capacitor is the best
choice. When polarized capacitors are used, the posi-
tive side of the capacitor should face the amplifier in-
put in most applications as the DC level there is held
BTL
F
C
C(highpass
i
i
and R
i
and the minimum input impedance R
Gain
2
i
R
1
+ R
)
i
f
F
).
i
c
f
2
is important to consider as it directly
, C
2
R
1
i
) to the load.
i
i
C
R
R
i
i
f
i
i
www.anpec.com.tw
is 20k
i
and the
is 0.2 F
i
(1)
from a
(2)
(3)
i
, is