TPA3002D2

SLOS402C − DECEMBER 2002 − REVISED JANUARY 2004

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Some audio systems require that the gain be limited in the VAROUT mode to a level that is comfortable for

headphone listening. The VARMAX terminal controls the maximum gain for the VAROUT channels.

The functionality of the VARDIFF and VARMAX pin are combined to fix the VAROUT channel gain. A block

diagram of the combined functionality is shown in Figure 35. The value obtained from the block diagram for

VAROUT_VOLUME is a DC voltage that can be used in conjunction with Table 2 to determine the VAROUT

channel gain. Table 2 lists the gain in VAROUT mode as determined by the VAROUT_VOLUME voltage in

reference to the voltage on VREF.

The timing of the volume control circuitry is controlled by an internal 30 Hz clock. This clock determines the rate

at which the gain changes when adjusting the voltage on the external volume control pins. The gain updates

every 4 clock cycles (nominally 133 ms based on a 30Hz clock) to the next step until the final desired gain is

reached. For example, if the TPA3002D2 is currently in the +0.53 db class-D gain step and the VOLUME pin

is adjusted for maximum gain at +36 dB, the time required for the gain to reach 36dB is 14 steps x 133 ms/step

= 1.862 seconds. Referencing Table 1, there are 14 steps between the +0.53 dB gain step and the maximum

gain step of +36 dB.

VARMAX (V)

VOLUME−VARDIFF

VARDIFF (V)

−

+

VOLUME (V)

NO

YES

VAROUT_VOLUME (V) = VOLUME (V) − VARDIFF (V)

VAROUT_VOLUME (V) = VARMAX (V)

Is VARMAX>

(VOLUME−VARDIFF)

?

Figure 35. Block Diagram of VAROUT Volume Control

0.5

3.1

5.6

2.10

2.00

2.11

2.21

Voltage on VOLUME Pin − V

Decreasing Voltage on VOLUME Terminal

Increasing Voltage on VOLUME Terminal

(40.1%*VREF)

(44.1%*VREF)

(42.3%*VREF)

(41.9%*VREF)

Figure 36. DC Volume Control Operation, VREF = 5 V