TA0105A View Datasheet(PDF) - Tripath Technology Inc.

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TA0105A

STEREO CLASS-T DIGITAL AUDIO AMPLIFIER DRIVER USING DIGITAL POWER PROCESSING (DPP™) TECHNOLOGY

Tripath Technology Inc. 

Tripath Technology, Inc. - Technical Information

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 TA0105A 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.

PERFORMANCE MEASUREMENTS OF A TA0105A AMPLIFIER

Tripath amplifiers operate by modulating the input signal with a high-frequency switching pattern. This

signal is sent through a low-pass filter (external to the TA0105A) that demodulates it to recover an

amplified version of the audio input. The frequency of the switching pattern is spread spectrum and

typically varies between 200kHz and 1.5MHz, which is well above the 20Hz – 22kHz audio band. The

pattern itself does not alter or distort the audio input signal but it does introduce some inaudible noise

components.

The measurements of certain performance parameters, particularly those that have anything to do with

noise, like THD+N, are significantly affected by the design of the low-pass filter used on the output of the

TA0105A and also the bandwidth setting of the measurement instrument used. Unless the filter has a

very sharp roll-off just past the audio band or the bandwidth of the measurement instrument ends there,

some of the inaudible noise components introduced by the Tripath amplifier switching pattern will get

integrated into the measurement, degrading it.

Tripath amplifiers do not require large multi-pole filters to achieve excellent performance in listening tests,

usually a more critical factor than performance measurements. Though using a multi-pole filter may

remove high-frequency noise and improve THD+N type measurements (when they are made with wide-

bandwidth measuring equipment), these same filters can increase distortion due to inductor non-linearity.

Multi-pole filters require relatively large inductors, and inductor non-linearity increases with inductor value.

EMULATING A TA0104A USING A TA0105A MODULE

This following information is provided as a legacy set of instructions. Tripath has recently

released a product named the TDA2500. The over-current circuit in the TDA2500 is much closer to

that in the TA0104A, as compared to the TA0105A. Thus, for new designs, when trying to replace

a TA0104A (or TA0102A or TA0103A), please use the TDA2500. A data sheet for the TDA2500 is

available at www.tripath.com.

The TA0105A and TA0104A are structurally very similar employing the same block diagram. The

TA0105A gain and Overvoltage/Undervoltage range is roughly double that of the TA0104A. The voltage

rating on the TA0105A hybrid components are 200V, thus operating at lower voltages does not cause any

problem assuming that the external, user selectable, components are properly chosen.

For ease of use, the “voltage shifting” components are external to theTA0105A, allowing the user to

choose the voltage range, depending on the specific application. A common application is emulating a

TA0104A with its associated gain and voltage range. Below is a list of instructions along with diagrams of

the modifications needed to implement a “TA0104A” design. It should be noted that if some intermediate

range is needed, that the feedback and overvoltage/undervoltage resistors can be adjusted based on the

equations given in previous sections of the Application Information.

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TA0105A – RW/ Rev. 2.2/05.05

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