EVB90401 Datasheet, PDF (5/6 Pages) Melexis Microelectronic Systems – MLX90401 Demo Board

EVB90401
MLX90401 Demo Board
1.5 Operation
To operate the Demo Board the following steps are necessary:
• Connect the motor windings and Hall effect sensors.
• Select 60° or 120° sensor electrical phasing depending on the motor used, with the push button
switch 60/120.
• Connect the power supply.
• Use the push button switches and potentiometer to control the motor.
2 Remarks
2.1 Using standard power supplies
When using normal power supplies that are normally found in laboratories, there is one thing to keep in
mind. Most of these power supplies cannot sink current. When an electrical motor is braked it acts as a
generator. This causes reverse currents to flow out of the motor. This energy cannot be absorbed by the
power supply, and the supply voltage can be raised by a large degree. The supply voltage may even go
higher than the breakdown voltage of certain components, including the MLX90401, and by doing
so destroy the circuit.
The solution for this issue is the following:
• Connect a high-power zener diode (5 Watt) across the power supply, with a zener voltage of a
few volts above the normal operating supply voltage.
• This zener diode will start to conduct if the supply voltage is raised above its zener voltage by the
motor. That way a path is created for the excessive current to flow.
• The supply voltage will also be limited to the zener voltage.
When a battery (e.g. a 12V car battery) is used, this problem does not occur, since the battery can absorb
the fly back energy from the motor with significantly raising the battery voltage.
2.2 Power off
When the board is powered off (e.g. using the On/Off switch) the MLX90401 is no longer powered.
However as in many applications the motor is still rotating after power off the motor generates a voltage
that is not clamped or limited. If this voltage exceeds the maximum voltage rating the MLX90401
could be destroyed.
The solution is either:
• To disable or brake the motor until standstill before powering off the board or application.
• Or to solder a power zener diode behind the switch between supply and ground that can drain the
motor fly back power after opening the switch. Mind that zener diode DZ1 is not suitable to drain
the motor power.
390119040101
Rev 002
Page 5 of 6
Application Note
15-Jul-05