TA0105A Datasheet, PDF (14/29 Pages) Tripath Technology Inc. – STEREO CLASS-T DIGITAL AUDIO AMPLIFIER DRIVER USING DIGITAL POWER PROCESSING (DPPTM ) TECHNOLOGY

Tripath Technology, Inc. - Technical Information
The MOSFET drivers in the TA0105A are operated from voltages obtained from VN12 and LO1COM for
the low-side driver, and bootstrap voltage (internally generated) and HO1COM for the high-side driver.
VN12 must be a regulated 12V above VNN.
N-Channel MOSFETs are used for both the top and bottom of the half bridge. The gate resistors, R_G, are
used to control MOSFET slew rate and thereby minimize voltage overshoots. Though not shown, the
gate diodes, D_G, reduce the MOSFET turn-off time, thus resucing cross conduction and idle supply
current.
CIRCUIT BOARD LAYOUT
The TA0105A 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 TA0105A and external mosfets 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 TA0105A evaluation board document, RB-TA0105A, available on the Tripath website,
at www.tripath.com.
The following components are important to place near either their associated TA0105A or output
MOSFET pins. The recommendations are ranked in order of layout importance, either for proper device
operation or performance considerations.
- The impedance of the output node (the connection between the top side MOSFET source to
bottom side MOSFET drain) must be minimized. Reducing the parasitic trace inductance is the
most effective way of limiting output node ringing. A flat, bar conductor, in parallel with the PCB
output node trace, is quite effective at minimizing the inductance thereby reducing output
transients due to the switching architecture.
- The capacitors, C_HBR, provide high frequency bypassing of the amplifier power supplies and will
serve to reduce spikes and modulation of the power supply rails. Please note that both mosfet
half-bridges must be decoupled separately. In addition, the voltage rating for C_HBR should be at
least 400V as this capacitor is exposed to the full supply range, VPP-VNN.
- The output diodes, D_O, are used to minimize overshoots/undershoots on the output node.
Please note that the proper connection of these is “Drain to Drain” and “Source to Source” as
shown in the Application/Test Circuit. Improper routing of these diodes will render them
useless due to PCB trace inductance.
- The gate resistors, R_G, should be located as close to the output MOSFET gates leads as
possible. In addition, the trace length from the pins LOx/HOx to the gate resistor should be
minimized. To reduce the loop area, a parallel trace from LOxCOM/HOxCOM should be routed
directly to the respective MOSFET source lead.
- C_FB 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 C_FB 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 TA0105A pin as possible.
Some components are not sensitive to location but are very sensitive to layout and trace routing.
- The routing of the sense resistors, R_S, must be Kelvin connected. This implies a direct trace
from the respective TA0105A pin to the sense resistor lead without interruption. If additional
14
TA0105A – RW/ Rev. 2.2/05.05