Datasheet

TMC2660 DATASHEET (Rev. 1.05 / 2016-JUL-14) 43
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14 Layout Considerations
The PCB layout is critical to good performance, because the environment includes both high-
sensitivity analog signals and high-current motor drive signals.
14.1 Sense Resistors
The sense resistors are susceptible to ground differences and ground ripple voltage, as the microstep
current steps result in voltages down to 0.5mV. No current other than the sense resistor currents
should flow through their connections to ground. Place the sense resistors close to chip with one or
more vias to the ground plane for each sense resistor.
The sense resistor layout is also sensitive to coupling between the axes. The two sense resistors
should not share a common ground connection trace or vias, because PCB traces have some
resistance.
14.2 Power MOSFET Outputs
The OA and OB dual pin outputs on the TMC2660 are directly connected electrically and thermally to
the drain of the MOSFETs of the power stage. A symmetrical, thermally optimized layout is required to
ensure proper heat dissipation of all MOSFETs into the PCB. Use thick traces and areas for vertical heat
transfer into the GND plane and enough vias for the motor outputs.
The printed circuit board should have a solid ground plane spreading heat into the board and
providing for a stable GND reference. All signals of the TMC2660 are referenced to GND. Directly
connect all GND pins to a common ground area.
The switching motor coil outputs have a high dV/dt, so stray capacitive coupling into high-impedance
signals can occur, if the motor traces are parallel to other traces over long distances.
14.3 Power Supply Pins
Both, the VSA and VSB pins, as well as the BRA and BRB pins conduct the full motor current for a
limited amount of time during each chopper cycle. Due to the resistance of bond wires connected to
these pins, the pins heat up. Therefore it is essential for current capability above 2A RMS to use a
wide PCB trace for cooing and in order to avoid additional heat up of the pins caused by PCB trace
resistance. This is simplified by also contacting the N.C. pins located next to VSA and VSB to the
supply voltage. Failure to do so might affect reliability; despite heat-up of bond wires might not be
visible with a thermal camera.
14.4 Power Filtering
The 470nF ceramic filtering capacitor on 5VOUT should be placed as close as possible to the 5VOUT
pin, with its GND return going directly to the nearest GND pin. Use as short and as thick connections
as possible. A 100nF filtering capacitor should be placed as close as possible from the VS pin to the
ground plane. The motor supply pins, VSA and VSB, should be decoupled with an electrolytic (>47 μF
is recommended) capacitor and a ceramic capacitor, placed close to the device.