TA0104A Datasheet, PDF (16/18 Pages) Tripath Technology Inc. – STEREO 500W (4Ω) CLASS-T DIGITAL AUDIO AMPLIFIER DRIVER USING DIGITAL POWER PROCESSING (DPPTM) TECHNOLOGY

Tripath Technology, Inc. - Technical Information
Efficiency Of A TA0104A Amplifier
The efficiency, η, of an amplifier is:
η = P_OUT/P_IN
The power dissipation of a TA0104A amplifier is primarily determined by the on resistance, R_ON, of
the output transistors used, and the switching losses of these transistors, P_SW. For a TA0104A
amplifier, P_IN (per channel) is approximated by:
P_IN = P_DRIVER + P_SW + P_OUT ((R_S + R_ON + R_COIL + R_L)/R_L)²
where:
P_DRIVER = Power dissipated in the TA0104A = 1.6W/channel
P_SW = 2 x (0.015) x Q_g (Q_g is the gate charge of M, in nano-coulombs)
R_COIL = Resistance of the output filter inductor (typically around 50mΩ)
For an 400W RMS per channel, 8Ω load amplifier using STW38NB20 MOSFETs, and an R_S of
50mΩ,
P_IN = P_DRIVER + P_SW + P_OUT ((R_S + R_ON + R_COIL + R_L)/R_L)²
= 1.6 + 2 x (0.015) x (95) + 400 x ((0.025 + 0.11 + 0.05 + 8)/8)²
= 1.6 + 2.85 + 419
= 423W
In the above calculation the R_{DS (ON)} of 0.065Ω was multiplied by a factor of 1.7 to obtain R_ON in order
to account for some temperature rise of the MOSFETs. (R_{DS (ON)} typically increases by a factor of 1.7
as for a typical MOSFET as temperature increases from 25ºC to 170ºC.)
So,
η = P_OUT/P_IN = 400/423 = 94%
This compares to the 90% measured efficiency (see Typical Performance graphs).
Technical Documentation
Please refer to the Tripath “Application Notes” section on our web page
(http://www.tripath.com/html/tech.htm#appnotes) for more information regarding evaluation, test and
design of Class-T amplifiers.
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TA104A – Rev. 3.1/06.00