TA3020 Ver la hoja de datos (PDF) - Tripath Technology Inc.

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Fabricante

TA3020

Stereo 300W (4Ω) Class-T Digital Audio Amplifier Driver using Digital Power Processing™ Technology

Tripath Technology Inc. 

TECHNICAL INFORMATION

INPUT

RF

CI

RI

OAOUT1

TA3020

V5

INV1

BIASCAP

20k

INV2

20k

OAOUT2

AGND

V5

+

-

AGND

Figure 6: Input Stage Setup for Bridging

The switching outputs, OUT1 and OUT2, are not synchronized, so a common inductor may not be

used with a bridged TA3020. For this same reason, individual zobel networks must be applied to

each output to load each output and lower the Q of each common mode differential LC filter.

Low-frequency Power Supply Pumping

A potentially troublesome phenomenon in single-ended switching amplifiers is power supply

pumping. This phenomenon is caused by current from the output filter inductor flowing into the

power supply output filter capacitors in the opposite direction as a DC load would drain current from

them. Under certain conditions (usually low-frequency input signals), this current can cause the

supply voltage to “pump” (increase in magnitude) and eventually cause over-voltage/under-voltage

shut down. Moreover, since over/under-voltage are not “latched” shutdowns, the effect would be an

amplifier that oscillates between on and off states. If a DC offset on the order of 0.3V is allowed to

develop on the output of the amplifier (see “DC Offset Adjust”), the supplies can be boosted to the

point where the amplifier’s over-voltage protection triggers.

One solution to the pumping issue it to use large power supply capacitors to absorb the pumped

supply current without significant voltage boost. The low-frequency pole used at the input to the

amplifier determines the value of the capacitor required. This works for AC signals only.

A no-cost solution to the pumping problem uses the fact that music has low frequency information

that is correlated in both channels (it is in phase). This information can be used to eliminate boost by

putting the two channels of a TA3020 amplifier out of phase with each other. This works because

each channel is pumping out of phase with the other, and the net effect is a cancellation of pumping

currents in the power supply. The phase of the audio signals needs to be corrected by connecting

one of the speakers in the opposite polarity as the other channel.

26

TA3020, Rev 2.1, 01.01

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