TMC5161 DATASHEET (Rev. 1.01 / 2018-NOV-20)
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29 Layout Considerations
29.1 Exposed Die Pads
The TMC5161 uses an exposed pad for each die to dissipate heat from the MOSFETs and the central
control chip to the board. For best electrical and thermal performance, use wide traces on more than
one PCB layer for all power signals, and interconnect them with a reasonable amount of solid,
thermally conducting vias between each die attach pad and the supply plane, resp. the output traces.
The OAx and OBx outputs are directly connected electrically and thermally to the drain of the low side
MOSFETs of the power stage in order to dissipate heat. 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 provide enough vias for vertical heat transfer near the
outputs. All high side MOSFETs are connected and cooled via the VM bar. Provide a solid, thermally
conductive connection to the supply plane and additional areas and vias for cooling.
The printed circuit board should have a solid ground plane spreading heat horizontally into the board
and providing for a stable GND reference. All signals of the TMC5161 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.
29.2 Power Supply Pins
Both, the VM pins and Oxx motor outputs, as well as the RSA and RSB 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 to use a wide PCB trace for
cooling and in order to avoid additional heat up of the pins caused by PCB trace resistance. Failure to
do so might affect reliability; despite heat-up of bond wires might not be visible with a thermal
camera.
29.3 Wiring GND
All signals of the TMC5161 are referenced to their respective GND. Directly connect all GND pins under
the device to a common ground area (GND, GNDP, GNDA and die attach pad). The GND plane right
below the die attach pad should be treated as a virtual star point. For thermal reasons, the PCB top
layer shall be connected to a large PCB GND plane spreading heat within the PCB.
Attention
Place the sense resistors and their GND connection near to the TMC5161 using a common GND plane
in order to avoid ringing leading to GND differences and to dangerous inductive peak voltages.
29.4 Supply Filtering
The 5VOUT output voltage ceramic filtering capacitor (2.2 to 4.7 µF recommended) should be placed as
close as possible to the 5VOUT pin, with its GND return going directly to the GNDA pin. This ground
connection shall not be shared with other loads or additional vias to the GND plane. Use as short and
as thick connections as possible. For best microstepping performance and lowest chopper noise an
additional filtering capacitor should be used for the VCC pin to GND, to avoid digital part ripple
influencing motor current regulation. Therefore, place a ceramic filtering capacitor (470nF
recommended) as close as possible (1-2mm distance) to the VCC pin with GND return going to the
ground plane. VCC can be coupled to 5VOUT using a 2.2 Ω or 3.3 Ω resistor in order to supply the
digital logic from 5VOUT while keeping ripple away from this pin. A 100 nF filtering capacitor should
be placed as close as possible to the VSA pin to ground plane. Make sure, that VS does not see
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