TMC5041 DATASHEET (Rev. 1.13 / 2017-MAY-16)
13
3.3 External 5V Power Supply
When an external 5V power supply is available, the power dissipation caused by the internal linear
regulator can be eliminated. This especially is beneficial in high voltage applications, and when
thermal conditions are critical. There are two options for using this external 5V source: either the
external 5V source is used to support the digital supply of the driver by supplying the VCC pin, or the
complete internal voltage regulator becomes bridged and is replaced by the external supply voltage.
3.3.1 Support for the VCC Supply
This scheme uses an external supply for all digital circuitry within the driver (Figure 3.3). As the digital
circuitry makes up for most of the power dissipation, this way the internal 5V regulator sees only low
remaining load. The precisely regulated voltage of the internal regulator is still used as the reference
for the motor current regulation as well as for supplying internal analog circuitry.
When cutting pin VCC from 5VOUT, make sure that the VCC supply comes up before or synchronously
with the 5VOUT supply to ensure a correct power up reset of the internal logic. A simple schematic
uses two diodes forming an OR of the internal and the external power supplies for VCC. In order to
prevent the chip from drawing part of the power from its internal regulator, a low drop 1A Schottky
diode is used for the external 5V supply path, while a silicon diode is used for the 5VOUT path. An
enhanced solution uses a dual PNP transistor as an active switch. It minimizes voltage drop and thus
gives best performance.
In certain setups, switching of VCC voltage can be eliminated. A third variant uses the VCC_IO supply
to ensure power-on reset. This is possible, if VCC_IO comes up synchronously with or delayed to VCC.
Use a linear regulator to generate a 3.3V VCC_IO from the external 5V VCC source. This 3.3V regulator
will cause a certain voltage drop. A voltage drop in the regulator of 0.9V or more (e.g. LD1117-3.3)
ensures that the 5V supply already has exceeded the lower limit of about 3.0V once the reset
conditions ends. The reset condition ends earliest, when VCC_IO exceeds the undervoltage limit of
minimum 2.1V. Make sure that the power-down sequence also is safe. Undefined states can result
when VCC drops well below 4V without safely triggering a reset condition. Triggering a reset upon
power-down can be ensured when VSA goes down synchronously with or before VCC.
+VM
+VM
VSA
VSA
5V Voltage
regulator
5V Voltage
regulator
5VOUT
5VOUT
100n
100n
4.7µ
4.7µ
LL4448
+5V
+5V
VCC
VCC
MSS1P3
VCC_IO
3.3V
regulator
470n
470n
100n
3.3V
VCC supplied from external 5V. 5V or 3.3V IO voltage.
VCC supplied from external 5V. 3.3V IO voltage generated from same source.
+VM
VSA
5V Voltage
regulator
5VOUT
100n
4.7µ
BAT54
+5V
10k
VCC
2x BC857 or
1x BC857BS
470n
4k7
VCC supplied from external 5V using active switch. 5V or 3.3V IO voltage.
Figure 3.3 Using an external 5V supply for digital circuitry of driver (different options)
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