Datasheet

TMC5130A DATASHEET (Rev. 1.11 / 2015-OCT-08) 18
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3.7 High Motor Current
When operating at a high motor current, the driver power dissipation due to MOSFET switch on-
resistance significantly heats up the driver. This power dissipation will heat up the PCB cooling
infrastructure also, if operated at an increased duty cycle. This in turn leads to a further increase of
driver temperature. An increase of temperature by about 100°C increases MOSFET resistance by
roughly 50%. This is a typical behavior of MOSFET switches. Therefore, under high duty cycle, high
load conditions, thermal characteristics have to be carefully taken into account, especially when
increased environment temperatures are to be supported. Refer the thermal characteristics and the
layout hints for more information. As a thumb rule, thermal properties of the PCB design become
critical for the TQFP-48 at or above 1.2A RMS motor current for increased periods of time. Keep in
mind that resistive power dissipation raises with the square of the motor current. On the other hand,
this means that a small reduction of motor current significantly saves heat dissipation and energy.
An effect which might be perceived at medium motor velocities and motor sine wave peak currents
above roughly 1.2A peak is an increasing negative impact of increased internal diode conduction on
the duration of the fast decay cycle of the spreadCycle chopper. This is, because the current
measurement does not see the full coil current during this phase of the sine wave, because an
increasing part of the current flows directly from the power MOSFETs’ drain to GND and does not flow
through the sense resistor. This in turn under some conditions may lead to a slight sine distortion of
the current wave when using spreadCycle. This effect with most motors does not negatively influence
the smoothness of operation, as it does not impact the critical current zero transition. It does not
occur with stealthChop and with classic chopper.
3.7.1 Reduce Linear Regulator Power Dissipation
When operating at high supply voltages, as a first step the power dissipation of the integrated 5V
linear regulator can be reduced, e.g. by using an external 5V source for supply. This will reduce overall
heating. It is advised to reduce motor stand still current in order to decrease overall power
dissipation. If applicable, also use coolStep. A decreased clock frequency will reduce power dissipation
of the internal logic. Further a decreased chopper frequency also can reduce power dissipation.
3.7.2 Operation near to / above 2A Peak Current
The driver can deliver up to 2.5A motor peak current. Considering thermal characteristics, this only is
possible in duty cycle limited operation. When a peak current up to 2.5A is to be driven, the driver
chip temperature is to be kept at a maximum of 105°C. Linearly derate the design peak temperature
from 125°C to 105°C in the range 2A to 2.5A output current (see Figure 3.8). Exceeding this may lead
to triggering the short circuit detection.
Die
Temperature
Peak coil
current
105°C
125°C
2A
Opearation not recommended
for increased periods of time
2.5A1.75A
115°C
135°C
1.5A
Limit by lower limit of
overtemperature threshold
Specified operational
range for max. 125°C
Derating
for >2A
High temperature
range
Current
limitation
2.25A
Figure 3.8 Derating of maximum sine wave peak current at increased die temperature