tk2070 Tripath Technology Inc., tk2070 Datasheet - Page 12

• Manufacturer Part Number: tk2070
• Description: Stereo 70w 4ohm Class-t Digital Audio Amplifier Driver Using Digital Power Processing Dpp Technology
• Manufacturer: Tripath Technology Inc.

A P P L I C A T I O N I N F O R M A T I O N
T K 2 0 7 0 B a s i c A m p l i f i e r O p e r a t i o 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 650kHz.
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 C
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 c u i t B o a r d L a y o u t
The TK2070 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 TK2070 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.
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.
12
FB
-
-
-
for each channel. Typical values of C
The capacitors C
will serve to reduce spikes across the supply rails. C
of the VDD pins. Please note that the four VDD pins must be decoupled separately. In
addition, the voltage rating for C
supply range.
C
lowers the output switching frequency by delaying the feedback signals. In addition, the
value of C
frequency difference greater than 40kHz. This minimizes in-band audio noise.
To minimize noise pickup and minimize THD+N, R
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.
FB
removes very high frequency components from the amplifier feedback signals and
FB
is different for channel 1 and channel 2 to keep the average switching
HBR
provide high frequency bypassing of the amplifier power supplies and
HBR
The switching patterns for the two channels are not
FB
are 390pF for channel 1 and 560pF for channel 2.
should be 50V as this capacitor is exposed to the full
T r i p a t h T e c h n o l o g y , I n c . - T e c h n i c a l I n f o r m a t i o n
FBC
HBR
should be located as close to the
should be kept within 1/8” (3mm)
TK2070 – MC/2.1/10-03