Tripath Technology, Inc. - Technical Information
In general, to enable placement as close to the TK2150, and minimize PCB parasitics, the
capacitors CFB, CB and CSW 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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To maximize the damping factor and reduce distortion and noise, the modulator
feedback connections should be routed directly to the pins of the output inductors. LO.
The output filter capacitor, CO, and zobel capacitor, CZ, should be star connected with
the load return. The output ground feedback signal should be taken from this star point.
The modulator feedback resistors, RFBA and RFBB, should all be grounded and attached
to 5V together. These connections will serve to minimize common mode noise via the
differential feedback.
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The feedback signals that come directly from the output inductors are high voltage and
high frequency in nature. If they are routed close to the input nodes, IN1 and IN2, the
high impedance inverting opamp pins will pick up noise. This coupling will result in
significant background noise, especially when the input is AC coupled to ground, or an
external source such as a CD player or signal generator is connected. Thus, care
should be taken such that the feedback lines are not routed near any of the input
section.
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To minimize the possibility of any noise pickup, the trace lengths of IN1 and IN2 should
be kept as short as possible. This is most easily accomplished by locating the input
resistors, RI and the input stage feedback resistors, RF as close to the TC2001 as
possible. In addition, the offset trim resistor, ROFB, which connects to either IN1, or IN2,
should be located close to the TC2001 input section.
TK2150 Grounding
Proper grounding techniques are required to maximize TK2150 functionality and performance.
Parametric parameters such as THD+N, Noise Floor and Crosstalk can be adversely affected if
proper grounding techniques are not implemented on the PCB layout. The following discussion
highlights some recommendations about grounding both with respect to the TK2150 as well as
general “audio system” design rules.
The TK2150 is divided into three sections: the input section, which is the TC2001, the MOSFET
driver section, which is the TP2150, and the output (high voltage) section, which is the output
MOSFETs. On the TK2150 evaluation board, the ground is also divided into distinct sections,
Analog Ground (AGND) and Power Ground (PGND). To minimize ground loops and keep the
audio noise floor as low as possible, the two grounds must be only connected at a single point.
Depending on the system design, the single point connection may be in the form of a ferrite bead
or a PCB trace.
The analog ground, must be connected to pin 20 on the TC2001 and pins 2 and 5 on the TP2150.
The ground for the V5 power supply should connect directly to pin 20 of the TC2001. Additionally,
any external input circuitry such as preamps, or active filters, should be referenced to pin 20 on
the TC2001. Special care must be used when connecting the NC pins of the TP2150 in order to
achieve the best noise performance. Pins 1, 3, 4, 8, 11, 12, 18, 19, 20, 22, 23, 24, 25, 61, 62, 63,
64 should be tied to Analog Ground. All of the other NC pins of the TP2150 should be left
floating.
For the power section, Tripath has traditionally used a “star” grounding scheme. Thus, the load
ground returns and the power supply decoupling traces are routed separately back to the power
supply. In addition, any type of shield or chassis connection would be connected directly to the
ground star located at the power supply. These precautions will both minimize audible noise and
enhance the crosstalk performance of the TK2150.
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TK2150 – Rev. 1.0/12.02
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
