Tripath Technology, Inc. - Technical Information
The MOSFET drivers in the TP2150 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 TK2150 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 TK2150 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 TK2150
evaluation board document, RB-TK2150, available on the Tripath website, at www.tripath.com.
The trace that connects the source of the top side output MOSFET to the drain of the bottom side
output MOSFET is very important. This connection should be as wide as possible and as short
as possible. Also a jumper wire of 16 gauge or more can by used in parallel with the trace to
reduce any trace resistance or inductance. Any resistance or inductance on this trace can cause
the switching output to over/undershoot potentially causing damage to both the TP2150 and the
output MOSFETs.
The following components are important to place near either their associated TK2150 or output
MOSFET pins. The recommendations are ranked in order of layout importance, either for proper
device operation or performance considerations.
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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. Locate
these capacitors as close to their respective TC2001 pin as possible.
-
DD and DS should be placed as close to the drain and source of the output MOSFETs
as possible. DD should be connected directly from the drain of the top side MOSFET to
the drain of the bottom side MOSFET. DS should be connected directly from the source
of the top side MOSFET to the source of the bottom side MOSFET. DD protects the
bottom side output MOSFET from output over/undershoots. DS protects the top side
output MOSFET from output over/undershoots. The over/undershoots are very high
speed transients, if DD and DS are placed too far away from the MOSFETs they will be
ineffective.
-
-
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. The feedback and feedback ground traces should be
routed together in parallel.
CB, CSW provides high frequency bypassing for the VN10 and bootstrap supplies. Very
high currents are present on these supplies.
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TK2150 – Rev. 1.0/12.02
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
