TA0104A Datasheet, PDF (10/18 Pages) Tripath Technology Inc. – STEREO 500W (4Ω) CLASS-T DIGITAL AUDIO AMPLIFIER DRIVER USING DIGITAL POWER PROCESSING (DPPTM) TECHNOLOGY

Tripath Technology, Inc. - Technical Information
Supply Voltage and Output Power
The relationship between the bipolar power supply voltage needed, V_S, for a given RMS output
power, P_OUT, into a given load, R_L, at a given level of THD (total harmonic distortion) is approximated
by:
V_S = (2 x R_L x P_OUT) ^0.5/(K x R_L/(R_L + R_ON + R_S + R_COIL))
where:
R_ON = The at-temperature R_DSON of the output transistors, M.
R_COIL = Resistance of the output filter inductor.
R_S = Sense Resistor
K = THD Factor, a number fixed by the algorithms in the TA0104A’s signal processor that
provides the relationship between THD at full output power of the amplifier and V_S. K
corresponds to THD at full output power as follows:
THD
K
0.1%
0.83
1%
0.95
10%
1.09
Typical measurement graphs of P_OUT versus supply voltage for various levels of THD are also
included in this data sheet to help determine the supply voltage.
Bridged Operation
Note that the two channels of a TA0104A amplifier can be used to provide a single, bridged amplifier
of almost four times the output power of one of the single-ended amplifier channels. To configure a
bridged amplifier, the input to one TA0104A channel must be the inverted signal of the input to the
other channel.
Low-frequency Power Supply Pumping
A potentially troublesome phenomenon in single-ended switching amplifiers is power supply pumping.
This 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) 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 is 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
driver determines the value of the supply capacitor required.
Another solution to the supply 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 TA0104A 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. The phase of the audio signals needs to be corrected by
connecting one of the speakers in the opposite polarity as the other channel.
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TA104A – Rev. 3.1/06.00