T E C H N I C A L I N F O R M A T I O N
the processor via FBKOUT1. Additional feedback information to account for ground bounce is
supplied via FBKGND1.
The MOSFET drivers in the TA3020 are operated from voltages obtained from VN10 and LO1COM
for the low-side driver, and VBOOT1 and HO1COM for the high-side driver. VN10 must be a
regulated 10V above VNN.
N-Channel MOSFETs are used for both the top and bottom of the half bridge. The gate resistors, RG,
are used to control MOSFET slew rate and thereby minimize voltage overshoots.
Circuit Board Layout
The TA3020 is a power (high current) amplifier that operates at relatively high switching frequencies.
The output of the amplifier switches between VPP and VNN at high speeds while driving large
currents. This high-frequency digital signal is passed through an LC low-pass filter to recover the
amplified audio signal. Since the amplifier must drive the inductive LC output filter and speaker
loads, the amplifier outputs can be pulled above the supply voltage and below ground by the energy
in the output inductance. To avoid subjecting the TA3020 to potentially damaging voltage stress, it
is critical to have a good printed circuit board layout. It is recommended that Tripath’s layout and
application circuit be used for all applications and only be deviated from after careful analysis of the
effects of any changes. Please refer to the TA3020 evaluation board document, EB-TA3020,
available on the Tripath website, at www.tripath.com.
The following components are important to place near their associated TA3020 pins and are ranked
in order of layout importance, either for proper device operation or performance considerations.
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-
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The capacitors CHBR provide high frequency bypassing of the amplifier power supplies and
will serve to reduce spikes across the supply rails. Please note that both mosfet half-
bridges must be decoupled separately. In addition, the voltage rating for CHBR should be
at least 150V as this capacitor is exposed to the full supply range, VPP-VNN.
CFB removes very high frequency components from the amplifier feedback signals and
lowers the output switching frequency by delaying the feedback signals. In addition, the
value of CFB is different for channel 1 and channel 2 to keep the average switching
frequency difference greater than 40kHz. This minimizes in-band audio noise.
To minimize noise pickup and minimize THD+N, RFBC should be located as close to the
TA3020 as possible. Make sure that the routing of the high voltage feedback lines is kept
far away from the input op amps or significant noise coupling may occur. It is best to
shield the high voltage feedback lines by using a ground plane around these traces as well
as the input section.
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CB, CSW provides high frequency bypassing for the VN10 and bootstrap supplies. Very
high currents are present on these supplies.
In general, to enable placement as close to the TA3020, and minimize PCB parasitics, the
capacitors listed above should be surface mount types, located on the “solder” side of the board.
Some components are not sensitive to location but are very sensitive to layout and trace routing.
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TA3020, Rev 2.1, 01.01
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
