TPA3003D2

SLOS406A − FEBRUARY 2003 − REVISED MARCH 2003

19

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APPLICATION INFORMATION

volume control operation (continued)

If using an analog potentiometer to control the gain, it should be connected between VREF and REFGND.

VREF can be connected to AVDDREF or an external voltage source, if desired. The first and second column

in Table 1 should be used to determine the point at which the gain changes depending on the direction that the

potentiometer is turned. If the voltage on the center tap of the potentiometer is increasing, the first column in

Table 1 should be referenced to determine the trip points. If the voltage is decreasing, the trip points in the

second column should be referenced.

The trip point, where the gain actually changes, is different depending on whether the voltage on the VOLUME

terminal is increasing or decreasing as a result of hysteresis about each trip point. The hysteresis ensures that

the gain control is monotonic and does not oscillate from one gain step to another. A pictorial representation

of the volume control can be found in Figure 26. The graph focuses on three gain steps with the trip points

defined in the first and second columns of Table 1. The dotted lines represent the hysteresis about each gain

step.

The timing of the volume control circuitry is controlled by an internal 60-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 67 ms based on a 60 Hz clock) to the next step until the final desired gain is

reached. For example, if the TPA3003D2 is currently in the +0.53 dB gain step and the VOLUME pin is adjusted

for maximum gain at +36 dB, the time required for the gain to reach +36 dB is 14 steps x 67ms/step = 0.938

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

of +36 dB.

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 26. DC Volume Control Operation, VREF = 5 V