AN2433 Freescale Semiconductor / Motorola, AN2433 Datasheet - Page 17

• Manufacturer Part Number: AN2433
• Description: 5V to 3V Design Considerations
• Manufacturer: Freescale Semiconductor / Motorola

Interfacing to Motor Control Parts
Analogue Signals
MOTOROLA
Sensed
Sensed
Voltage
Voltage
A motor drive system, controlled by an MCU, includes the power supply stage,
the power transistors and their gate drivers, and the motor.
The AC input line is rectified in the input power supply stage and it provides the
DC voltage for switching the power transistors that deliver the power to the
motor.
The transition from 5V to 3.3V for motor control applications needs to be
considered both for the analogue and digital signals.
In motor control applications, the feedback signals are typically analogue in
nature. Most motor control applications utilize voltage and current feedback for
control algorithms and safe operation. The auxiliary feedback signals, like
temperature sensing, depend on the requirements of the actual application.
A voltage measurement (e.g. back EMF) is commonly used as an indication of
motor speed. This signal is digitised by the MCU’s on-board A/D converter.
Resistor dividers are used to ensure that the voltage at the input of the A/D
converter (MCU pins) does not exceed the maximum rated voltage (
The two (and sometimes three) resistors R1 and R2 are normally used for high
motor voltage. It is necessitated because of the maximum voltage rating of the
resistors. For lower voltage motor control applications, even a single resistor is
usually sufficient. Moving to a lower MCU operating voltage will not have any
impact on 3.3 V MCU applications.
Freescale Semiconductor, Inc.
R1
R1
For More Information On This Product,
5V to 3V Design Considerations
Figure 15. Voltage Sensor
Go to: www.freescale.com
R2
R2
R3
R3
Vss
Vss
Interfacing to Motor Control Parts
Input
Input
A/D
A/D
MCU
MCU
Figure 15
AN2433/D
17
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