Datasheet


     
SLOS230D − NOVEMBER 1998 − REVISED OCTOBER 2002
23
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
application schematic
Figure 51 is a schematic diagram of a typical handheld audio application circuit, configured for a gain of
−10 V/V.
Audio
Input
Bias
Control
V
DD
6
5
7
V
O
+
V
DD
3
1
2
4
BYPASS
IN
SE/BTL
V
DD
/2
C
I
0.47 µF
R
I
10 kΩ
C
S
1 µF
C
B
2.2 µF
RF
50 kΩ
SHUTDOWN
V
O
−8
GND
From System Control
C
F
5 pF
CC
330 µF
1 kΩ
100 kΩ
V
DD
100 kΩ
−
+
−
+
0.1 µF
Figure 51. TPA711 Application Circuit
The following sections discuss the selection of the components used in Figure 51.
component selection
gain setting resistors, R
F
and R
I
The gain for each audio input of the TPA711 is set by resistors R
F
and R
I
according to equation 5 for BTL mode.
(5)
BTL gain +*2
ǒ
R
F
R
I
Ǔ
BTL mode operation brings about the factor 2 in the gain equation due to the inverting amplifier mirroring the
voltage swing across the load. Given that the TPA711 is a MOS amplifier, the input impedance is very high;
consequently input leakage currents are not generally a concern, although noise in the circuit increases as the
value of R
F
increases. In addition, a certain range of R
F
values is required for proper start-up operation of the
amplifier. Taken together it is recommended that the effective impedance seen by the inverting node of the
amplifier be set between 5 kΩ and 20 kΩ. The effective impedance is calculated in equation 6.
(6)
Effective impedance +
R
F
R
I
R
F
) R
I