3 differential input – Texas Instruments TPA0242 User Manual
Page 22
The TPA0242 Audio Power Amplifier Evaluation Module
3-6
Details
Potentiometer R2 adjusts the gain of the internal preamp stage of the TPA0242
amplifier by adjusting the control voltage applied to the VOLUME terminal (pin
3) of the IC. Rotating the potentiometer slider clockwise decreases the applied
control voltage, resulting in a higher volume. Table 3–1 shows the relationship
between the control voltage applied to the VOLUME terminal and the effective
amplifier gain. Headphone gain is reduced by 6 dB.
Table 3–1. TPA0242 EVM BTL Volume Settings
VOLUME (Pin 3)
BTL
VOLUME (Pin 3)
BTL
VOLUME (Pin 3)
BTL
FROM
(V)
TO
(V)
BTL
GAIN
(dB)
FROM
(V)
TO
(V)
BTL
GAIN
(dB)
FROM
(V)
TO
(V)
BTL
GAIN
(dB)
0
0.15
20
1.28
1.39
–2
2.52
2.63
–24
0.15
0.28
18
1.39
1.5
–4
2.63
2.74
–26
0.28
0.39
16
1.5
1.62
–6
2.74
2.86
–28
0.39
0.5
14
1.62
1.73
–8
2.86
2.97
–30
0.5
0.61
12
1.73
1.84
–10
2.97
3.08
–32
0.61
0.73
10
1.84
1.95
–12
3.08
3.2
–34
0.73
0.84
8
1.95
2.07
–14
3.2
3.31
–36
0.84
0.95
6
2.07
2.18
–16
3.31
3.42
–38
0.95
1.06
4
2.18
2.29
–18
3.42
3.54
–40
1.06
1.17
2
2.29
2.41
–20
3.54
5
–85
1.17
1.28
0
2.41
2.52
–22
Since the overall gain of the amplifier is set by the internal preamp stage and
not by the power amplifier stage, the TPA0242 maintains the same total
harmonic distortion (THD) at even the highest gain settings.
3.2.3
Differential Input
The TPA0242 line inputs allow the use of a single-ended or differential audio
source. The differential input stage of the amplifier cancels any noise that
appears on both input lines of a channel. To use the TPA0242 EVM with a
differential source, connect the positive lead of the audio source to the R LINE–
(L LINE–) input and the negative lead from the audio source to the R IN+
(L IN+) input. To use the TPA0242 with a single-ended source, ac-ground the
R IN+ and L IN+ inputs and apply the audio signal to the R LINE– and L LINE–
inputs. Line and headphone inputs share common positive inputs. If using
separate line and headphone inputs, R IN+ and L IN+ should be ac-grounded.
If using differential inputs, line and headphone inputs must be the same. In a
single-ended input application, the R IN+ and L IN+ inputs should be ac
grounded at the audio source instead of at the device inputs for best noise
performance.