apa3010 Anpec Electronics Corporation, apa3010 Datasheet - Page 10

• Manufacturer Part Number: apa3010
• Description: 3w Mono Low-voltage Audio Power Amplifier
• Manufacturer: Anpec Electronics Corporation

BTL Operation
The APA3010/1 output stage (power amplifier) has two
pairs of operational amplifiers internally, allowed for dif-
ferent amplifier configurations.
The power amplifier’ s OP1 gain is setting by Ri and Rf
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 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 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 placed 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 APA3010/1, also
creates a second advantage over SE amplifiers. Since
the differential outputs, OUTP and OUTN, are biased at
half-supply, 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.6 - Jun., 2009
Application Information
APA3010/1
Figure 1. APA3010/1 Internal Configuration
Circuit
ANPEC Electronics Corp.
Vbias
OP1
OP2
OUTP
OUTN
R
L
10
Input Resistance, R
The gain for audio input of the APA3010/1 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
directly affects the low frequency performance of the circuit.
Consider the example where R
cation calls for a flat bass response down to 50Hz. Equa-
tion 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
This leakage current creates a DC offset voltage at the
input to the amplifier that reduces useful headroom, es-
pecially in high gain applications. For this reason, a low-
leakage tantalum or ceramic capacitor is the best choice.
When polarized capacitors are used, the positive side of
the capacitor should face the amplifier input in most appli-
cations as the DC level of the amplifier input is held at
V
pacitor polarity in the application
DD
i
+R
/2. Please note that it is important to confirm the ca-
f
BTL Gain = -2 x
C
C
(highpass)=
f
i
=
, C
i
2 x20k xf
) to the load.
i
1
must be considered carefully because it
i
2 x20k xC
i
i
i
(20k ) form a high-pass filter with
C
R
R
and R
f
i
1
f
).
i
i
is 10k
.
www.anpec.com.tw
(1)
(2)
(3)
and the specifi-
i
is 0.16 F, so
i
, is required
i
and the