TA0103A View Datasheet(PDF) - Tripath Technology Inc.

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TA0103A

Stereo 250W (4Ω) Class-T Digital Audio Amplifier Driver using Digital Power Processing (DPP™) Technology

Tripath Technology Inc. 

Tripath Technology, Inc. - Technical Information

Turn-on & Turn-off Noise

If turn-on or turn-off noise is present in a TA0103A amplifier, the cause is frequently due to other

circuitry external to the TA0103A. While the TA0103A has circuitry to suppress turn-on and turn-off

transients, the combination of the power supply and other audio circuitry with the TA0103A in a

particular application may exhibit audible transients. One solution that will completely eliminate turn-

on and turn-off pops and clicks is to use a relay to connect/disconnect the amplifier from the

speakers with the appropriate timing at power on/off. The relay can also be used to protect the

speakers from a component failure (e.g. shorted output MOSFET), which is a protection mechanism

that some amplifiers have. Circuitry external to the TA0103A would need to be implemented to

detect these failures.

Output Filter Design

One advantage of Tripath amplifiers over PWM solutions is the ability to use higher-cutoff-frequency

filters. This means any load-dependent peaking/droop in the 20kHz audio band potentially caused

by the filter can be made negligible. This is especially important for applications where the user may

select a 4-Ohm or 8-Ohm speaker. Furthermore, speakers are not purely resistive loads and the

impedance they present changes over frequency and from speaker model to speaker model.

Tripath recommends designing the filter as a 2nd order, 80kHz LC filter. Tripath has obtained good

results with LF = 18uH and CF = 0.22uF for a nominal impedance of 8 .

The core material of the output filter inductor has an effect on the distortion levels produced by a

TA0103A amplifier. Tripath recommends low-mu type-2 iron powder cores because of their low loss

and high linearity.

Tripath also recommends that an RC damper be used after the LC low-pass filter. No-load operation

of a TA0103A amplifier can create significant peaking in the LC filter, which produces strong

resonant currents that can overheat the output MOSFETs and/or other components. The RC

dampens the peaking and prevents problems. Tripath has obtained good results with RD = 33Ω and

CD = 0.1uF.

It is highly recommended that the design process for a TA0103A amplifier include an analysis of the

interaction of intended speaker(s) with the LC filter and RC damper to ensure the desired frequency

response is attained. Component values for the LC filter and RC damper may need to be altered

from the Tripath suggestions to achieve the required response.

Grounding

Tripath recommends not connecting analog ground (AGND) to power ground (PGND) externally, as

this connection is already made internal to the TA0103A.

Circuit Board Layout

Considerable care needs to be taken in the layout of the circuit board for a TA0103A amplifier. The

high currents flowing through PCB traces and the inductive effects due to the switching frequencies

involved can cause large overshoot and undershoot voltages if care is not taken. A general rule to

follow is to keep the PCB trace of each signal path to/from each lead of each output MOSFET as

short as physically possible.

Certain circuit functions in a TA0103A amplifier cannot share PCB return paths with other functions

because of the resistive and inductive effects of the switching currents and frequencies used. These

so-called ‘Kelvin’ paths must each have a dedicated PCB trace from the TA0103A to their

destination. The following signals should be treated as Kelvin paths: OCS1H+, OCS1H-, OCS1L+,

OCS1L-, OCS2H+, OCS2H-, OCS2L+, OCS2L-, FDBKN1, FDBKN2, GNDKELVIN1 and

GNDKELVIN2.

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TA0103 – Rev 3.3/06.00

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