Datasheet
SLOS230D − NOVEMBER 1998 − REVISED OCTOBER 2002
27
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
SE/BTL
operation
The ability of the TPA711 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 TPA711, 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 TPA711
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 TPA711 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
1 kΩ
100 kΩ
V
DD
100 kΩ
−
+
−
+
0.1 µF
Figure 52. TPA711 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 shut
down 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 applications section. 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.