Tripath Technology, Inc. - Preliminary Information
Break-Before-Make (BBM) Timing Control
The complementary half-bridge power MOSFETs require a deadtime between when one transistor is
turned off and the other is turned on (break-before-make) in order to minimize shoot through currents.
The TDA1400 has an analog input pin that controls the break-before-make timing of the output
transistors. Connecting RBBM from the BBMSET pin (pin 10) to analog ground creates a current that
defines the BBM setting by the following equation.
BBM (nsec) = 2 X RBBM + 7
where RBBMSET is in kΩ’s and 5kΩ < RBBM* < 100kΩ
* A RBBMSET of 0Ω will yield a BBM setting of 0nsec.
There is tradeoff involved in making this setting. As the delay is reduced, distortion levels improve but
shoot-through and power dissipation increase. 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.
Recommended MOSFETs
The following devices are capable of achieving full performance, both in terms of distortion and efficiency,
for the specified load impedance and voltage range.
Device Information – Recommended MOSFETs
Part Number
FQP19N10
FQP22P20
Manufacturer
Fairchild Semiconductor
Fairchild Semiconductor
BVDSS (V)
100
-100
ID (A)
19
-22
Qg (nC)
25
50
Package
TO220
TO220
RDS(on) (Ω)
0.078
0.096
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 6-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, 102kHz 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
TDA1400 amplifier. Tripath recommends low-mu type-2 iron powder cores because of their low loss and
high linearity (available from Micrometals, www.micrometals.com).
Tripath also recommends that an RC damper be used after the LC low-pass filter. No-load operation of a
TDA1400 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 RZ = 10Ω and CZ = 0.22uF.
Performance Measurements of a TDA1400 Amplifier
Tripath amplifiers operate by modulating the input signal with a high-frequency switching pattern. This
signal is sent through a low-pass filter (external to the TDA1400) that demodulates it to recover an
amplified version of the audio input. The frequency of the switching pattern is spread spectrum and
typically varies between 200kHz and 1.5MHz, which is well above the 20Hz – 22kHz audio band. The
pattern itself does not alter or distort the audio input signal but it does introduce some inaudible noise
components.
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TDA1400 – Rev. 0.65/KLi/02.06
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
