TA0104A Datasheet, PDF (14/18 Pages) Tripath Technology Inc. – STEREO 500W (4Ω) CLASS-T DIGITAL AUDIO AMPLIFIER DRIVER USING DIGITAL POWER PROCESSING (DPPTM) TECHNOLOGY

Tripath Technology, Inc. - Technical Information
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 L_F = 18uH and C_F = 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
TA0104A 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 TA0104A 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 R_D = 33Ω and C_D = 0.1uF.
It is highly recommended that the design process for a TA0104A 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 TA0104A.
Circuit Board Layout
Considerable care needs to be taken in the layout of the circuit board for a TA0104A 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 TA0104A 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 TA0104A 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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TA104A – Rev. 3.1/06.00