mlx90401 Melexis Company, mlx90401 Datasheet - Page 8

• Manufacturer Part Number: mlx90401
• Description: Brushless Dc Motor Controller Not For New Designs!
• Manufacturer: Melexis Company

7.6 Pulse width modulation
The use of pulse width modulation (PWM) provides an energy efficient method of controlling the motor
speed by varying the average voltage applied to each stator winding during the commutation sequence. As
C
comparator terminates the bottom drive output conduction when the positive-going ramp of C
greater than the Speed Adjust Input. In order to minimize dissipation in the internal diodes of the external
top switch transistors, due to free-wheeling currents, the PWM acts also on the top FET, by turning it on
when the corresponding bottom FET is off. The pulse width modulator timing diagram is shown below.
(Braking of the motor does not depend on the PWM setting. It is always done at 100%.)
7.7 Drive outputs
The bottom drivers consist of a push-pull driver between the 12V reference voltage and ground.
The top drivers use an improved push-pull architecture to guarantee proper drive of the top FETs. Because
the top driver utilizes a bootstrap/charge pump combination, use of only N-channel power FETs for the
three-phase bridge is possible. This leads to a reduced system cost.
Internal charge pumps precharge the boost capacitors to ensure full drive of upper power FETs at start-up.
During normal operation, boost is maintained with an external diode and capacitor. The charge pumps
compensate for potential leakage currents, in order to ensure that the upper power FETs are driven
properly at all time.
3901090401
Rev 005
OSC
discharges, the oscillator allows conduction of the top and bottom drive outputs. The PWM
Bottom Drive
V
Note 1. Top and Bottom Drive Output Diagrams assume
commutation logic gives 1 for bottom switch and 0 for top
switch. In case the commutation logic gives 0 for bottom
switch and 1 for top switch, the PWM does not act on them.
Top Drive
Speed
RC Input
Output
Output
Osc
PWM Timing Diagram (note 1)
Input
Figure 3: PWM timing diagram
Page 8 of 13
Brushless DC Motor Controller
MLX90401
OSC
Data sheet
becomes
Oct/05