MLX90401
Brushless DC Motor Controller
7.3 Commutation decoding and output control logic
An internal digital circuit converts the signals from the Hall-effect position sensors into the proper
sequencing of top and bottom drive outputs.
60° or 120° sensor electrical phasing can be selected by an external pin (60°/120° Select, pin 11).
The Forward/Reverse input (pin 6) is used to change the direction of motor rotation.
If the /Brake input (pin 9) is pulled low, bottom drivers are turned on, while top drivers are turned off, thus
braking the motor.
These six inputs all have internal pull-up resistors (3.3kΩ to 5V).
Inputs 60°/120° Select, Fwd/Rev and /Brake are debounced to make sure that the device doesn’t enter the
wrong state, due to noise and/or spikes.
The fact that these signals are debounced, also means that there is a delay in these signals. Whenever one
of the external signals that are debounced is changed, it takes time till the outputs change accordingly (ca.
25ms for the 60°/120° Select and Fwd/Rev inputs, ca. 3ms for /Brake).
After start-up, the outputs are disabled for a given time, in order to provide for the time necessary for the
debouncing circuits on 60°/120° Select and Fwd/Rev to settle and output the correct signal.
(/Brake is debounced with a shorter time so settles a lot sooner.)
7.4 Oscillator
The frequency of the internal sawtooth oscillator is set by the values selected for timing components R
OSC
and C
OSC
(see Figure 4 : Typical application). Capacitor C
OSC
is charged from the Reference Output (Pin 2)
through Resistor R
OSC
and discharged by an internal discharge transistor. The ratio of the ramp peak and
valley voltages referred to the Reference Output voltage are typically 0.65V and 0.3V respectively. To
provide a good compromise between audible noise and output switching efficiency, an oscillator frequency
in the range of 20 to 30 kHz is recommended.
7.5 Disable
Pin 7, Speed Adjust Input/Disable, is to be connected to an external potentiometer, used to set motor
speed.
The input can also be used as a Disable input, turning off all output drivers. This Disable input can be used
in many ways. A thermal switch could be used to provide thermal protection. Or a Hall switch could be used
to provide protection against overcurrent, etc.
Disable has a higher priority than /Brake. If for instance Disable is active, braking will not have any effect. If
/Brake is active at the moment that Disable is made active, all braking will be stopped.
3901090401
Rev 005
Page 7 of 13
Data sheet
Oct/05
MELEXIS [ Melexis Microelectronic Systems ]
