TPA3003D2

SLOS406A − FEBRUARY 2003 − REVISED MARCH 2003

18

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APPLICATION INFORMATION

when to use an output filter (continued)

0.1

µF

0.1

µF

0.47

µF

33

µH

33

µH

OUTP

OUTN

L1

L2

C1

C2

C3

Figure 24. Typical LC Output Filter, Cutoff Frequency of 41 kHz, Speaker Impedance = 8

Ω

1 nF

Ferrite

Chip Bead

OUTP

OUTN

Ferrite

Chip Bead

1 nF

Figure 25. Typical Ferrite Chip Bead Filter (Chip bead example: Fair-Rite 2512067007Y3)

volume control operation

The VOLUME terminal controls the internal amplifier gain. This pin is controlled with a dc voltage, which should

not exceed VREF. Table 1 lists the gain 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 21 in the

Application Information 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 TPA3003D2 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.