apa2071 Anpec Electronics Corporation, apa2071 Datasheet - Page 15

• Manufacturer Part Number: apa2071
• Description: Stereo 3.1w Non-inverting Audio Power Amplifier With Dc Volume Control
• Manufacturer: Anpec Electronics Corporation

APA2071
The power amplifier’ s (OP1) gain is set by internal unity
gain and input audio signal comes from internal volume
control amplifier while the second amplifier (OP2) is in-
ternally 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 signals of with
both amplifiers with identical in magnitude but out of phase
180°. Consequently, the differential gain for each chan-
nel is 2 x (Gain of SE mode).
By driving the load differentially through outputs OUTP
and OUTN, an amplifier configuration is commonly re-
ferred to as bridged mode is established. BTL mode op-
eration is different from the classical single-ended (SE)
amplifier configuration where one side of its load is con-
nected to ground.
A BTL amplifier design has a few distinct advantages over
the SE configuration, as it provides differential drive to the
load, thus doubles the output swing for a specified sup-
ply voltage.
Four times the output power is possible as compared
with a SE amplifier under the same conditions. A BTL
configuration, such as the one used in APA2071, also
creates a second advantage over SE amplifiers. Since
the differential outputs, ROUTP, ROUTN, LOUTP, and
LOUTN, are biased at half-supply, DC voltage doesn’ t
have to exist across the load. This eliminates the need
for an output coupling capacitor which is required in a
single supply, SE configuration.
Copyright
Rev. A.1 - Aug., 2008
Bridge-Tied Load (BTL) Operation
The APA2071’ s output stage of each channel, which con-
sists of one pair of operational amplifiers, provides op-
tion for BTL operation shown as figure 1.
Function Description
Volume Control
amplifier output
signal
Figure 1: APA2071 Internal Configuration
Bias Voltage
Generator
ANPEC Electronics Corp.
(each channel)
OP1
OP2
OUTN
OUTP
R
L
15
To consider the single-supply SE configuration shown in
Typical Application Circuit, a coupling capacitor is required
to block the DC offset voltage from reaching the load.
These capacitors can be quite large (approximately 33 F
to 1000 F) so they tend to be 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:
Easy switch between BTL and SE modes is one of its
most important costs saving features for the APA2071.
This feature eliminates the requirement for an additional
headphone amplifier in applications where internal ste-
reo speakers are driven in BTL mode but external head-
phone or speakers must be accommodated.
Inside of the APA2071, two separated amplifiers drive
OUTP and OUTN (See Figure 1). The SE/BTL input con-
trols the operation of the follower amplifier that drives
LOUTP and ROUTN.
Control of the SE/BTL input can be a logic-level TTL source
or a resistor divider network or the stereo headphone
jack with switch pin as shown in Typical Application Circuit.
Single-Ended (SE) Operation
SE/BTL Mode Selection Function
Figure 2: SE/BTL Input Selection by Phonejack Plug
APA2071 is in the BTL mode.
impedance state, which configures the APA2071 as
SE driver from OUTP. I
one-half in SE mode.
When SE/BTL keeps low, the OP2 turns on and the
When SE/BTL keeps high, the OP2 is in a high output
SE/BTL
C
bypass
100k
x 130k
1
V
DD
DD
is reduced by approximately
2R
1k
1
i
C
i
Control
www.anpec.com.tw
Pin
2R
Headphone Jack
1
L
C
C
Tip
Ring
Sleeve
(1)