TMC260 and TMC261 DATASHEET (Rev. 2.05 / 2012-NOV-05)
49
17.3 Thermal Characteristics
Parameter
Symbol Conditions
Typ
Unit
Thermal resistance bridge
transistor junction to ambient,
one bridge chopping, fixed
polarity
RTHA12 soldered to 2 layer
PCB
88
°K/W
Thermal resistance bridge
transistor junctions to
ambient, two bridges
chopping, fixed polarity
Thermal resistance bridge
transistor junction to ambient,
one bridge chopping, fixed
polarity
Thermal resistance bridge
transistor junctions to
ambient, two bridges
chopping, fixed polarity
RTHA22 soldered to 2 layer
PCB
68
84
51
°K/W
°K/W
°K/W
RTHA14 soldered to 4 layer
PCB (pessimistic)
RTHA24 soldered to 4 layer
PCB (pessimistic)
If the device is to be operated near its maximum thermal limits, care has to be taken to provide a
good thermal design of the PCB layout in order to avoid overheating of the power MOSFETs
integrated into the TMC260 and TMC261. As the TMC26x use discrete MOSFETs, power dissipation in
each MOSFET needs to be looked over carefully.
Worst case power dissipation for the individual MOSFET is in standstill, with one coil operating at the
maximum current, because one full bridge in this case takes over the full current. This scenario can be
avoided with power down current reduction. As the single MOSFET temperatures cannot be
monitored, it is a good practice to react to the temperature pre-warning by reducing motor current,
rather than relying on the overtemperature switch off.
Note
Check MOSFET temperature under worst case conditions not to exceed 150°C, especially for TMC260
and TMC261 in design using a thermal camera to validate your layout.
Figure 17.1 One TMC260 operating at 1.4A RMS (2A peak), other TMC260 devices at 1.1A RMS
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