T E C H N I C A L I N F O R M A T I O N
BBM1
BBM0
Delay
120 ns
80 ns
40 ns
0 ns
0
0
1
1
0
1
0
1
Table 1: BBM Delay
The tradeoff involved in making this setting is that as the delay is reduced, distortion levels improve
but shoot-through and power dissipation increase. Both the 40nS and 0nS settings are NOT
recommended due the high level of shoot-thru current that will result. Thus, BBM1 should be
grounded in most applications. All typical curves and performance information was done with using
the 80ns or 120ns BBM setting. The actual amount of BBM required is dependent upon other
component values and circuit board layout, the value selected should be verified in the actual
application circuit/board. It should also be verified under maximum temperature and power
conditions since shoot-through in the output MOSFETs can increase under these conditions,
possibly requiring a higher BBM setting than at room temperature.
Output Filter Design
One advantage of Tripath amplifiers over PWM solutions is the ability to use higher-cutoff-frequency
filters. This means 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, 100kHz LC filter. Tripath has obtained good
results with LF = 11uH and CF = 0.22uF.
The core material of the output filter inductor has an effect on the distortion levels produced by a
TA3020 amplifier. Tripath recommends low-mu type-2 iron powder cores because of their low loss
and high linearity (available from Micrometals, www.micrometals.com). The specific core used on
the EB-TA3020 was a T106-2 wound with 29 turns of 16AWG wire.
Tripath also recommends that an RC damper be used after the LC low-pass filter. No-load operation
of a TA3020 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 = 20Ω and CD = 0.22uF.
Bridging the TA3020
The TA3020 can be bridged by returning the signal from OAOUT1 to the input resistor at INV2.
OUT1 will then be a gained version of OAOUT1, and OUT2 will be a gained and inverted version of
OAOUT1 (see Figure 6). When the two amplifier outputs are bridged, the apparent load impedance
seen by each output is halved, so the minimum recommended impedance for bridged operation is 8
ohms.
TA3020, Rev 2.1, 01.01
25
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
