Datasheet
TPA311
350-mW MONO AUDIO POWER AMPLIFIER
SLOS207C – JANUARY 1998 – REVISED MAY 2003
27
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
SE/BTL
operation
The ability of the TPA311 to easily switch between BTL and SE modes is one of its most important cost saving
features. This feature eliminates the requirement for an additional earphone amplifier in applications where
internal speakers are driven in BTL mode but external earphone or speaker must be accommodated. Internal
to the TPA311, two separate amplifiers drive V
O
+ and V
O
–. The SE/BTL input (terminal 3) controls the operation
of the follower amplifier that drives V
O
– (terminal 8). When SE/BTL is held low, the amplifier is on and the TPA311
is in the BTL mode. When SE/BTL
is held high, the V
O
– amplifier is in a high output impedance state, which
configures the TPA311 as an SE driver from V
O
+ (terminal 5). I
DD
is reduced by approximately one-half in SE
mode. Control of the SE/BTL
input can be from a logic-level TTL source or, more typically, from a resistor divider
network as shown in Figure 52.
Bias
Control
5
7
V
O
+
3
1
2
4
BYPASS
IN
SE/BTL
SHUTDOWN
V
O
– 8
GND
C
C
330
µF
1 kΩ
100 kΩ
V
DD
100 kΩ
–
+
–
+
0.1
µF
Figure 52. TPA311 Resistor Divider Network Circuit
Using a readily available 1/8-in. (3,5 mm) mono earphone jack, the control switch is closed when no plug is
inserted. When closed the 100-kΩ/1-kΩ divider pulls the SE/BTL
input low. When a plug is inserted, the 1-kΩ
resistor is disconnected and the SE/BTL
input is pulled high. When the input goes high, the V
O
– amplifier is
shutdown causing the BTL speaker to mute (virtually open-circuits the speaker). The V
O
+ amplifier then drives
through the output capacitor (C
C
) into the earphone jack.
using low-ESR capacitors
Low-ESR capacitors are recommended throughout this application. A real (as opposed to ideal) capacitor can
be modeled simply as a resistor in series with an ideal capacitor. The voltage drop across this resistor minimizes
the beneficial effects of the capacitor in the circuit. The lower the equivalent value of this resistance the more
the real capacitor behaves like an ideal capacitor.