TPA3003D2

SLOS406A − FEBRUARY 2003 − REVISED MARCH 2003

20

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APPLICATION INFORMATION

FADE operation

The FADE terminal is a logic input that controls the operation of the volume control circuitry during transitions

to and from the shutdown state and during power-up.

A logic low on this terminal places the amplifier in the fade mode. During power-up or recovery from the

shutdown state (a logic high is applied to the SD terminal), the volume is smoothly ramped up from the mute

state, −75 dB, to the desired volume setting determined by the voltage on the volume control terminal.

Conversely, the volume is smoothly ramped down from the current state to the mute state when a logic low is

applied to the SD terminal. 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 class-D 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 67 ms/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.

Figure 27 shows a scope capture of the differential output (measured across OUT+ and OUT−) with the amplifier

the SD terminal at the time defined in the figure. The figure depicts the outputs transitioning from one gain step

to the next lower step at approximately 67 ms/step.

A logic high on this pin disables the volume fade effect during transitions to and from the shutdown state and

during power-up. During power-up or recovery from the shutdown state (a logic high is applied to the SD

terminal), the transition from the mute state, −75 dB, to the desired volume setting is less than 1 ms. Conversely,

the volume ramps down from current state to the mute state within 1 ms when a logic low is applied to the SD

terminal.

Figure 28 shows a scope capture of the differential output with the fade effect disabled. The outputs transition

to the lowest gain state within 1ms of applying a logic low to the SD terminal.

SD = 0V

GND

Figure 27. Differential Output With FADE (Terminal 30) Held Low