Tripath Technology, Inc. - Technical Information
Note that the two channels of a TA0103A 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 TA0103A channel must be the inverted signal of the input to the
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 in magnitude) 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. This works for AC signals only.
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 TA0103A 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.
VN12 is an additional supply voltage required by the TA0103A. VN12 must be 12 volts more
positive than the nominal VSNEG. VN12 must track VSNEG, so if an unregulated supply is used for
VSNEG, the design of the supply for VN12 must behave accordingly. Generating the VN12 supply
requires some care.
The proper way to generate the voltage for VN12 is to use a 12V-supply voltage referenced to
the VSNEG supply rather than to ground (PGND). Figure 4 shows the correct way to power the
One method to generate the VN12 supply voltage is to use a positive 12V IC regulator to drop
PGND down to 12V (relative to VSNEG). Care must be exercised with this method because some
IC regulators such as the LM340 series will not function properly with a large voltage drop across
the regulator, resulting in damage to the TA0103A.
TA0103 – Rev 3.3/06.00