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EVB90401
MLX90401 Demo Board Introduction
The MLX90401 Demo Board described in this document is designed to show the operation and performance of the Brushless DC Motor Controller and to simplify the design of new applications. The Demo Board provides the necessary external components to facilitate evaluation of the MLX90401 without having to design and construct external circuitry. Several control switches and a potentiometer are available on the Board. A regulated DC power supply is the only input signal. A brushless DC motor with Hall effect sensors is NOT included with the Demo Board, but any can be used.
Ordering Information
Part No. EVB90401A EVB90401B Power supply range of target application 12V to 24V 20V to 40V
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Application Note 15-Jul-05
EVB90401
MLX90401 Demo Board 1 Demo Board description
1.1 Schematic
SW1 ON/OFF
R1 (see text)
V+ 0 Vref HA HB HC 0
IC1 MLX90401 1 Supply Voltage VREF Out Hall "A" Input Hall "B" Input Hall "C" Input Fwd/Rev Input Speed Adjust Input / Disable Oscillator R/C /Brake Input Analog Ground 60/120 Select Input Power Ground Cap Boost "A" Gate Top "A" Feedback "A" Cap Boost "B" Gate Top "B" Feedback "B" Cap Boost "C" Gate Top "C" Feedback "C" Gate Bottom "A" Gate Bottom "B" Gate Bottom "C" 24
R2 1k5
DZ1 15V
C1 330u/ 63V
C2 100n
D3 VREF C4 22u/ 25V P1 100k Speed R4 1k C5 100n
2 3 4 5 6 7 8 9 10
TP2
D2 LED
23
R5
22 21
C7 10n
Q1
D4
20
D6
R6 ROSC 10k
19 18
C8 10n
Q2
M1 M2 M3
D7
D5
17
R7 COSC 5nF
16 15
C9 10n
Q3
R8
14
Q4 Q5 R5 ... R10 = 22R Q1 ... Q6 = IRF530 D3 ... D5 = 1N4148 D6 ... D8 = 1N4007 Q6
D8
11
Disable Fw/Rev Brake 60/120
R9
13
12
TP1
R10
1.2 Board layout
The following diagram shows a schematic overview of the most important parts of the Demo Board:
MLX90401 Demo Board OFF ON
V+
Speed adjust
M1 M2 M3 Disable
0 Vref HA HB HC
MLX 90401
pin1
0
Brake
60/120
Fw/Rev
Disable
Brake
390119040101 Rev 002
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Application Note 15-Jul-05
EVB90401
MLX90401 Demo Board
1.3 Functional Description
The Demo Board mainly consists of the following blocks: * 15V regulator with an On/Off switch and a power-on indication LED * Connectors for power supply, Hall effect sensors and brushless DC motor * Three push button switches for controlling the motor: Brake, Forward/Reverse (Fw/Rev) and Disable * One push button switch for setting 60 or 120 sensor electrical phasing of the motor (60/120) * A potentiometer to control motor speed (Speed adjust) * 1 on-board MLX90401 Brushless DC Motor Controller * External components for oscillator, charge boost and protection. The main purpose of the board is to demonstrate the functionality and capabilities of the MLX90401. With a power supply and a brushless DC motor connected, the buttons and potentiometer can be used to fully control the motor. An on-board zener diode regulator provides a voltage of 15V for the chip. That way the external power supply - which is also supplied to the motor - can be as high as 40V. R1 (and if necessary also the zener diode) can be optimized for a specific power supply voltage (see Remarks below). Two versions of the Demo Board can be ordered, each for a specific power supply voltage range. (See Order Information for more details.) The Vref pin (output of the MLX90401) serves as a 12V supply for the Hall effect sensors. The Disable input can be used for protection purposes. Pulling the Disable input low turns off all drivers. When the motor is disabled in such a way, it will come to a standstill due to friction. No active braking is applied. Any sort of switch can be used to pull the Disable input low. An option is the use of a thermal switch. This thermal switch can be used to monitor the temperature of the drivers MOSFETs. If the MOSFETs get too hot, the thermal switch will pull the Disable input low.
R3 10k P1 100k R4 1k
6 7 Fwd/Rev Input Speed Adjust Input / Disable Oscillator R/C /Brake Input Analog Ground 60/120 Select Input Power Ground Feedback "B" Cap Boost "C" Gate Top "C" Feedback "C" Gate Bottom "A" Gate Bottom "B" Gate Bottom "C" 19 18 17
Speed C3 4n7 C6 100n
8 9 10 11
Q3
16 15
Q4
14
Fw/Rev Brake 60/120
Q5
13
12
Q6
T Disable
Thermally linked
Another possibility is the use of a Hall effect switch. When the current through the driver MOSFETs reaches a certain threshold, the magnetic field induced in the sense coil will exceed the Hall effect switch threshold. The Hall effect switch should then switch to the "ON" state, and in that way pull the Disable input low. This in turn switches off all drivers.
390119040101 Rev 002
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Application Note 15-Jul-05
EVB90401
MLX90401 Demo Board
R3 10k P1 100k Speed C3 4n7 C6 100n R4 1k
6 7 8 9 10 11 Fwd/Rev Input Speed Adjust Input / Disable Oscillator R/C /Brake Input Analog Ground 60/120 Select Input Power Ground Feedback "B" Cap Boost "C" Gate Top "C" Feedback "C" Gate Bottom "A" Gate Bottom "B" Gate Bottom "C" 19 18 17
Q3
16 15
Q4
14
Fw/Rev Brake 60/120
Q5
13
12
Q6
Disable Hall switch e.g. US5881
L1
Also, a sense resistor can be used to measure the current through the motor. The current will produce a voltage drop across the sense resistor. This voltage, amplified and filtered, can be compared with a reference voltage. If the voltage (proportional to the current) exceeds the reference voltage, the Disable pin is pulled low and drivers are switched off.
ROSC 10k P1 100k Speed C6 100n COSC 5nF R4 1k
6 7 8 9 10 11 Fwd/Rev Input Speed Adjust Input / Disable Oscillator R/C /Brake Input Analog Ground 60/120 Select Input Power Ground Feedback "B" Cap Boost "C" Gate Top "C" Feedback "C" Gate Bottom "A" Gate Bottom "B" Gate Bottom "C" 19 18 17
Q3
16 15
Q4
14
Fw/Rev Brake 60/120
Q5
13
12
Q6
+ COMP -
FILTER
A
RSENSE
VREF
A Test Pin is available on the Demo Board as a connection point for the Disable signal. A Test Pin is also available on the Brake signal.
1.4 Bill of Materials for the Demo
* * * * A Demo Board with on-board MLX90401 A regulated power supply (laboratory power supply, battery etc.) A brushless DC motor (Oscilloscope)
390119040101 Rev 002
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Application Note 15-Jul-05
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
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Application Note 15-Jul-05
EVB90401
MLX90401 Demo Board
2.3 Optimum value of R1
The minimum value of resistor R1 is determined by the minimum power supply voltage available for the chip. VCHIP,MIN should be at least 8V (undervoltage VUV) for the drivers to work. VCHIP,MIN = VSUPPLY,MIN - R1 x ICHIP For example: VCHIP,MIN = 24V - 220R x 35mA = 16.3V The maximum value of the resistor determines the power dissipation of the resistor: PR1 = (VSUPPLY - VCHIP) x ICHIP For example: PR1 = (24V - 15V) x 35mA = 315mW For instance, if a standard 12V battery is used, make R1=100R. VCHIP = 12V - 100R x 35mA = 8.5V > VUV = 8V PR1 = (12V - 8.5V) x 35mA = 122.5mW VSUPPLY VCHIP R1 PR1 (V) (V) (Ohm) (W) > 23.0 15 220 > 0.37 16.0 8.3 220 0.27 12.0 8.5 100 0.13 8.0 8.0 0 0.00 Table 1: Recommended value of R1 in function of supply voltage (with DZ1 = 15V zener diode)
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Phone: +32 1367 0495 E-mail: sales_europe@melexis.com
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390119040101 Rev 002
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Application Note 15-Jul-05

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