TPA3002D2

SLOS402C − DECEMBER 2002 − REVISED JANUARY 2004

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22

1 nF

Ferrite

Chip Bead

OUTP

OUTN

Ferrite

Chip Bead

1 nF

Figure 34. Typical Ferrite Chip Bead Filter (Chip bead example: Fair-Rite 2512067007Y3)

VOLUME CONTROL OPERATION

Three pins labeled VOLUME, VARDIFF, and VARMAX control the class-D volume when driving speakers and

the VAROUT volume. All of these pins are controlled with a dc voltage, which should not exceed VREF.

When driving speakers in class-D mode, the VOLUME pin is the only pin that controls the gain. Table 1 lists

the gain in class-D mode as determined by the voltage on the VOLUME pin in reference to the voltage on VREF.

If using a resistor divider to fix the gain of the amplifier, the VREF terminal can be directly connected to

AVDDREF and a resistor divider can be connected across VREF and REFGND. (See Figure 29 in the

Applications Section). For fixed gain, calculate the resistor divider values necessary to center the voltage

between the two percentage points given in the first column of Table 1. For example, if a gain of 10.7 dB is

desired, the resistors in the divider network can both be 10 k

Ω. With these resistor values, a voltage of 50%

× VREF will be present at the VOLUME pin and result in a class-D gain of 10.7 dB.

If using a DAC to control the class-D gain, VREF and REFGND should be connected to the reference voltage

for the DAC and the GND terminal of the DAC, respectively. For the DAC application, AVDDREF would be left

unconnected. The reference voltage of the DAC provides the reference to the internal gain circuitry through the

VREF input and any fluctuations in the DAC output voltage will not affect the TPA3002D2 gain. The percentages

in the first column of Table 1 should be used for setting the voltages of the DAC when the voltage on the

VOLUME terminal is increased. The percentages in the second column should be used for the DAC voltages

when decreasing the voltage on the VOLUME terminal. Two lookup tables should be used in software to control

the gain based on an increase or decrease in the desired system volume. This is explained further in a section

below.

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 36. The graph focuses on three gain steps with the trip points

defined in the first and second columns of Table 1 for class-D gain. The dotted lines represent the hysteresis

about each gain step.

VARDIFF AND VARMAX OPERATION

The TPA3002D2 allows the user to specify a difference between the class-D gain and VAROUT gain. This is

desirable to avoid any listening discomfort when plugging in headphones. When interfacing with the variable

outputs, the VARDIFF and VARMAX pins control the VAROUT channel gain proportional to the gain set by the

voltage on the VOLUME pin. When VARDIFF = 0 V, the difference between the class-D gain and the VAROUT

gain is 16 dB. As the voltage on the VARDIFF terminal is increased, the VAROUT channel gain decreases.

Internal to the TPA3002D2 device, the voltage on the VARDIFF terminal is subtracted from the voltage on the

VOLUME terminal and this value is used to determine the VAROUT gain.