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  • Controlling Relay Driven Motor using S9S12VR48AF0VLF

  • Created: Jul 23, 2015

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Summary

Interfacing a motor with a microcontroller gives us an easier way of controlling it. The programmability of a microcontroller makes it perfect for motor control applications. But one disadvantage of using a microcontroller for motor controls is that sometimes or most of the time, the high current passing through the coil of the motor is affecting the microcontroller’s performance. Also, the blowback voltage generated by the motor when it’s power supply is suddenly cut harms the microcontroller pin circuitry or sometimes blow up the entire microcontroller chip.


The circuit in this reference design shows the capability of the Freescale S9S12VR48AF0VLF microcontroller to handle inductive loads such as a relay driven motor. This reference design demonstrates basic driving of motor by using S9S12VR48AF0VLF two low side drivers and one of its high side driver to rotate the motor in forward or reverse direction. The high side driver provides signal to PP1 or PS2 pin when the forward or reverse button is pressed. Depending on which button was pressed, either of the two low side drivers will give a low output to energize one of the two twin relays coil to move the motor in forward or reverse direction. For advanced method of controlling the motor with this microcontroller, the forward/reverse button in this circuit can be replaced with a much more sophisticated digital control.


The S9S12VR48AF0VLF microcontroller can operate with a 12V DC voltage supply which is an advantage since most of the high powered motors run in 12V supply and also 12V batteries are highly available in market. The device has a built-in voltage regulator system that can supply the microcontroller internally and provide external current to the components within the control unit. Also, this microcontroller has a built-in voltage level sensor so that when the whole system is powered by a battery, it can sense that the battery is running out of power and operates in low power mode. With careful observation and proper designing, Freescale was able to produce S9S12VR48AF0VLF designed to drive inductive loads such as motors. The design of this S9S12VR48AF0VLF microcontroller is ideal for automotive & industrial relay driven motor applications.