Texas Instruments manual ±1. TPA0242 EVM BTL Volume Settings, Differential Input

The TPA0242 Audio Power Amplifier Evaluation Module

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	TO	GAIN	FROM	TO	GAIN	FROM	TO	GAIN
(V)	(V)	(dB)	(V)	(V)	(dB)	(V)	(V)	(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.

3.2.3Differential 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.

3-6 Details