Texas Instruments TPA3003D2 - Manual (Page 19)

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
Class-D Gain − dB
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