Tripath Technology, Inc. - Technical Information
A P P L I C A T I O N I N F O R M A T I O N
T K2019 Basic Amp lifier Op eratio n
The TC2001 is a 5V CMOS signal processor that amplifies the audio input signal and converts the
audio signal to a switching pattern. This switching pattern is spread spectrum with a typical idle
switching frequency of about 700kHz. The switching patterns for the two channels are not
synchronized and the idle switching frequencies should differ by at least 40kHz to avoid increasing
the audio band noise floor. The idle frequency difference can be accomplished by offsetting the value
of CFB for each channel. Typical values of CFB are 390pF for channel 1 and 560pF for channel 2.
The TPS1035 is a MOSFET output stage that level-shifts the signal processor’s 5V switching patterns
to the power supply voltages and drives the power MOSFETs. The power MOSFETs are N-channel
devices configured in half-bridges and are used to supply power to the output load. The outputs of
the power MOSFETs must be low pass filtered to remove the high frequency switching pattern. A
residual voltage from the switching pattern will remain on the speaker outputs when the
recommended output LC filter is used, but this signal is outside of the audio band and will not affect
audio performance.
C i r cu i t B o ard L ayo u t
The TK2019 is a power (high current) amplifier that operates at relatively high switching frequencies.
The output of the amplifier switches between VDD and GND 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 inductanor. To avoid subjecting the TK2019 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.
The following components are important to place near their associated TC2001/TPS1035 pins and
are ranked in order of layout importance, either for proper device operation or performance
considerations.
-
The capacitors CHBR provide high frequency bypassing of the amplifier power supplies and
will serve to reduce spikes across the supply rails. CHBR should be kept within 1/8” (3mm)
of the VCC pins. Please note that the four VDD pins must be decoupled separately. In
addition, the voltage rating for CHBR should be 35V as this capacitor is exposed to the full
supply range.
-
-
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
TC2001 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.
In general, to enable placement as close to the TC2001/TPS1035, and minimize PCB parasitics, the
capacitors listed above (with the exception of the bulk capacitors) should be surface mount types.
11
TK2019 – MC/2.1/10-03
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
