apa3012 Anpec Electronics Corporation, apa3012 Datasheet - Page 14

• Manufacturer Part Number: apa3012
• Description: 3w Mono Low-voltage Audio Power Amplifier
• Manufacturer: Anpec Electronics Corporation

BTL Operation
The APA3012 output stage (power amplifier) has two pairs
of operational amplifiers internally, allowed for different
amplifier configurations.
Figure 1. APA3012 Internal Power Amplifier Configura-
tion
The power amplifier’ s OP1 gain is setting by R
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
ide ntic al in m agnitu de bu t out of ph ase 18 0°.
Consequently, the differential gain for each channel is 2
x (Gain of SE mode).
By driving the load differentially through outputs OUTP
and OUTN, an amplifier configuration commonly referred
to 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
the 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 sup-
ply voltage.
When under the same conditions, a BTL amplifier has
four times the output power of a SE amplifier. A BTL
configuration, such as the one used in APA3012, also
creates a second advantage over SE amplifiers. Since
the differential outputs, OUTP and OUTN are biased at
half-supply, and it is not necessary for DC voltage to be
across the load. This eliminates the need for an output
coupling capacitor which is required in a single supply,
SE configuration.
Copyright
Rev. A.2 - Dec., 2008
Application Information
APA3012
R
i
ANPEC Electronics Corp.
Circuit
Vbias
OP1
R
f
OP2
OUTP
OUTN
RL
i
and R
f
14
Input Resistance, R
The gain for audio input of the APA3012 is set by the
external resistors (R
BTL mode operation brings the factor of 2 in the gain
equation due to the inverting amplifier mirroring the volt-
age swing across the load. The input resistance will af-
fect the low frequency performance of audio signal.
Input Capacitor, C
In the typical application, an input capacitor, C
to allow the amplifier to bias the input signal to the proper
DC level for optimum operation. In this case, C
input impedance R
the corner frequency determined in the following equa-
tion :
The value of C
fects the low frequency performance of the circuit. Con-
sider the example where R
calls for a flat bass response down to 50Hz. Equation is
reconfigured as below :
When input resistance is considered, the C
a value in the range of 0.22 F to 1.0 F would be chosen.
A further consideration for this capacitor is the leakage
path from the input source through the input network
(R
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 ca-
pacitor is the best choice. When polarized capacitors are
used, the positive side of the capacitor should face the
amplifier input in most applications as the DC level there
is held at V
level. Please note that it is important to confirm the ca-
pacitor polarity in the application.
i
+R
BTL Gain = -2 x
f
C
C
f
(highpass)=
i
, C
=
i
) to the load. This leakage current creates a DC
2 x20k xf
DD
/2, which is likely higher than the source DC
i
is important to consider as it directly af-
1
i
i
2 x20k xC
i
i
(20k ) form a high-pass filter with
C
and R
R
R
f
i
1
i
f
is 20k
).
i
and the specification
www.anpec.com.tw
i
is 0.16 F, so
i
, is required
i
and the
(1)
(2)
(3)