Abstract:
A method and apparatus of interfacing a Hall sensor to a commutation circuit comprises receiving output signals from the Hall sensor; detecting when the Hall sensor output signals are within a predetermined range; generating commutation output signals when the Hall sensor output signals are in a predetermined state for a predetermined period of time; and locking out a change in the commutation output signals for a second predetermined period of time.

Description:
FIELD OF THE INVENTION 
     The invention pertains to a motor control circuits, in general, and to Hall effect sensor circuit utilized with a brushless direct current motor, in particular. 
     BACKGROUND OF THE INVENTION 
     It is common to utilize Hall sensors to determine motor rotor position. Unbuffered Hall sensors generate low amplitude signals that are directly proportional to the motor magnetic field. These signals are sinusoidal and typically in a range of 100 millivolts peak-to-peak. The Hall sensors are typically disposed within the motor housing, increasing the likelihood that the output signal will have electrical noise superimposed thereon. 
     The effect of noise on the smaller signals produced by Hall sensors can result in drive circuitry producing unwanted multiple drive pulses as the sensor output voltage approaches and crosses zero. One result of multiple pulses as the sensor voltage goes through zero is rattling of the motor stator and output switch overstress as the outputs repetitively switch back and forth between phases during commutation. 
     SUMMARY OF THE INVENTION 
     In accordance with the principles of the invention, a circuit for use with an unbuffered Hall sensor is provided. The circuit comprises a first circuit coupleable to the Hall sensor to provide first output signals when the magnitude of signals from the Hall sensor within a first predetermined voltage magnitude range. A first time dependent circuit is coupled to the zero crossing detector circuit. The first time dependent circuit generates second output signals if the first output signals have a predetermined relationship for a first predetermined time period. A lockout timer circuit is coupled to the first time dependent circuit. 
     In the illustrative embodiment of the invention, a motor driver circuit is controlled by the second output signals. 
     In accordance with one aspect of the invention an integrated circuit has the first circuit, the time dependent circuit, the lockout timer and the motor driver circuit formed thereron. 
     A commutation circuit in accordance with the principles of the invention comprises a pair of terminals coupleable to a Hall sensor; zero crossing detection circuitry coupled to the pair of terminals; a timer coupled to the zero crossing detection circuitry; a commutation latch coupled to the zero crossing detection circuitry via the timer; a lockout timer coupled to the commutation latch and the timer; and motor driver circuitry coupled to the commutation latch. 
     Further in accordance with the principles of the invention, the commutation circuit comprises an integrated circuit having the zero crossing detection circuitry, the timer, the commutation latch, the lockout timer and the motor drive circuitry formed thereon. 
     A method of interfacing a Hall sensor to a commutation circuit comprises receiving output signals from the Hall sensor; detecting when the Hall sensor output signals are within a predetermined range; generating commutation output signals when the Hall sensor output signals are in a predetermined state for a predetermined period of time; and locking out a change in the commutation output signals for a second predetermined period of time. 
     In the illustrative embodiment of the invention the predetermined range is a zero crossing voltage range. 
     Further in accordance with the principles of the invention, the second predetermined period of time is selected to prevent noise signals superimposed on the Hall sensor output signals from affecting the generating of the commutation output signals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention will be better understood from a reading of the following detailed description of the drawing in which like reference designators are used to identify like elements in the various drawing figures, and in which; 
         FIG. 1  is a block diagram of a motor control circuit to which the present invention is particularly well suited; 
         FIG. 2  is a more detailed diagram of the motor control circuit of  FIG. 1  connected to a cooling fan; 
         FIG. 3  is a table that defines the function of each terminal of the motor control circuit of  FIG. 2 ; 
         FIGS. 4 and 5  are graphs showing motor speed as a function of the input voltage to the motor control circuit of  FIG. 1 ; 
         FIG. 6  illustrates the motor speed as a function of control voltage in table form; 
         FIG. 7  illustrates a circuit in accordance with the principles of the invention; and 
         FIG. 8  shows waveforms at points in the circuit of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     A motor controller  100  of the illustrative embodiment is a full featured two phase half wave variable speed brushless motor controller having complete functionality for a fan control system. Motor controller  100  provides a selectable slope pulse width modulator (PWM) with double pulse suppression for efficient speed control that is compatible with an analog voltage or varying duty cycle digital pulse train, a programmable minimum speed set input, an uncommitted op amp with a reference for speed control signal scaling, a Hall sensor amplifier with noise immunity circuitry for proper drive sequencing, adaptive non-overlapping commutation logic for reduced supply current spiking, on-chip 1.0 Ω power MOSFETs for direct coil drive. Protective and diagnostic features provided by motor controller  100  include an internal fault timer with auto start retry, motor kick start timer to insure proper start up, programmable cycle-by-cycle current limiting, power supply under voltage lockout, and over temperature thermal shutdown, and a combined frequency generator/rotor lock output for status reporting. 
     Motor controller  100  may be used in thermal open or closed loop systems. Motor controller  100  can be controlled by simple NTC or PTC thermistors, Simistor™ silicon temperature sensors, and complex digital or microcontroller temperature monitors. 
     Turning now to  FIG. 1 , controller  100  for speed control of motor  200  includes a pulse width modulator logic or PWM circuit  101 , commutation logic for proper drive sequencing  103 , direct motor drive  105 , current limiter  107 , and a programmable fault timer  109  with time power down and kick start features. Controller  100 , fully integrated on a single chip  102  contains all required functions for implementing fan speed control. 
     A more detailed block diagram of motor controller  100  shown in  FIG. 2 . A brief description of the pin functions is provided in  FIG. 3 . 
     Motor  200  includes rotor  201  and stator windings  203 ,  205 . A rotator position sensor  207  is provided with motor  200 . In a typical motor fan arrangement, a Hall effect device sensor is utilized as sensor  207 . Motor  200  includes connections Ø 1 , Ø 2 , a sensor outputs H+ and H− and power connections. 
     Motor controller  100  efficiently controls motor speed of a motor  200  by the use of pulse width modulation. Motor  200  includes two windings  203 ,  205 . The voltage applied to the speed control input, pin  10 , provides control of the motor speed by varying the drive percent on-time or conduction time of the phase  1  and phase  2  outputs φ 1 , φ 2  during the commutation cycle. The control signal at speed control input pin  10  can be in the form of an analog voltage ranging from 1.0 V to 3.0 V, or a variable duty cycle digital pulse train having a low state maximum of 0.98 V and a high state minimum of 3.02 V. The control signal transfer slope, speed control voltage to percent on-time, can be programmed via a slope select input at pin  11 . When pin  11  is connected to ground, an increase in control voltage or a digital high state results in an increase in motor drive on-time. When pin  11  is unconnected, an increase in control voltage or a digital high state results in a decrease in drive on-time. 
     A second control input is made available at pin  6  for setting a minimum motor speed. It has a control transfer that is similar to that of pin  10  and is designed be programmed from an analog voltage that ranges from 1.0 V to 3.0 V, which can be derived from the reference. The minimum speed programmed at this input will take control if it is greater than the speed indicated at pin  10 . 
       FIG. 4  shows the motor drives percent on-time versus the speed control input voltage with pin  11  connected to ground for positive slope control. Notice that there are two defined outcomes when the speed control input voltage falls below that of the minimum speed set. The first is that the motor remains at the programmed minimum speed setting and this is selected by loading the reference with 2.0 mA or more to disable auto power down. The second outcome is that the motor turns off after 1.0 second and this is selected by loading the reference with 1.0 mA or less to enable auto power down. 
       FIG. 5  shows the motor drives percent on-time versus the speed control input voltage with pin  11  unconnected for negative slope control. The minimum speed operating characteristics are selected in the same manner as above but with the defined outcomes now occurring when the speed control input voltage rises above that of the minimum speed set. 
     The programmed minimum motor speed can be disabled by connecting pin  6  to ground if pin  11  is also at ground, or by connecting pin  6  to the reference if pin  11  is unconnected. When controlling the motor speed from a variable duty cycle digital pulse train, the minimum speed set feature is not available and pin  6  must be connected to V DD , pin  4 .  FIG. 6  shows the speed control operation in table form. 
     For applications that do not require speed control, the device can easily be programmed for maximum motor speed without requiring any additional components. This is accomplished by connecting pins  6  and  10  to the reference output when pin  11  is at ground, or by connecting pins  6  and  10  to ground when pin  11  is open. 
     Rotor position of motor  200  is detected by a single Hall sensor  207  to enable proper motor drive commutation. The H+ and H− inputs to controller  100  are designed to interface with a wide variety of economical  4  pin unbuffered ‘naked’ or  3  pin buffered ‘digital’ type Hall sensors. The unbuffered types provide a low level output signal that is directly proportional to the applied magnetic field. These sensors connect directly to inputs H+ and H−. The inputs have a differential sensitivity of 20 mV with a common mode voltage range that extends from ground to V DD -1.5 V. By extending the input range to include ground, the need of a series ground lead resistor for offsetting the Hall output is eliminated. 
     Controller  100  provides enhanced noise rejection by combining a small level of input hysteresis with a zero crossing detector and a timed lockout. 
     Buffered Hall sensors provide a high level output signal that changes state in direct response the rotor magnetic pole transitions. This output signal is single ended and can be applied to either the H+ or H− input while biasing the unused input to a level that is half the sensors output voltage swing. Economical buffered Hall sensors typically have an open collector NPN output which requires a pull up resistor to the motor supply voltage V M . 
     Turning now to  FIG. 7  a circuit providing enhanced noise immunity for unbuffered Hall sensors is shown. Hall sensor  207  outputs H+ and H− are coupled to a first circuit coupleable to said Hall sensor providing first output signals when the magnitude of signals from said Hall sensor is within a first predetermined voltage magnitude range. In this embodiment, the first circuit comprises a pair of zero crossing detectors  701 ,  703 . In other embodiments the predetermined voltage magnitude range may be at some voltage range offset from zero. Hall sensor outputs H+ and H− are coupled to the inputs of a pair of zero crossing detectors  701 ,  703 . Each zero crossing detector  701 ,  703  provides a low level output when the input is less than, or more than a predetermined voltage, respectively. In the illustrative embodiment, that predetermined voltage is 10 millivolts.  FIG. 8  illustrates Hall sensor output at node A and the outputs of zero crossing detector  701  at node B and zero crossing detector  703  at node C. A next state latch  705  has its set S and reset R inputs coupled to zero crossing detectors  701 ,  703  respectfully. The Q′ and Q outputs of latch  705  are coupled to AND gates  709 ,  711 , respectively. The waveforms at points D and E, corresponding to latch outputs Q′ and Q are shown in HG.  8 . The outputs of zero crossing detectors  701 ,  703  are also coupled to the inputs of a zero detector  707 . Zero detector  707  comprises a NOR gate. The output waveform at the output F of zero detector  707  is shown in  FIG. 8 . The output of zero detector  707  is also coupled to inputs of AND gates  709 ,  711 . The outputs of gates  709 ,  711  are coupled to inputs of a shift register timer and decoder circuit  713 . The outputs of shift register timer and decoder circuit  713  are coupled to a commutation latch  715 . One output Q′ of commutation latch  715  is coupled to an edge detector  717  which is used to trigger a lockout timer  719 . Lockout timer  719  provides a control input to shift register timer and decoder circuit  713 . The waveform G at the output Q′ of commutation latch and the output waveforms H and I of edge detector  717  and lockout timer  719 , respectively, are shown in  FIG. 8 . 
     During zero crossing detector  707  outputs high state as shown in waveform F, the data from the next state latch  705  must be constant for a first predetermined time before the commutation latch  715  is updated. Once updated, the commutation latch  715  data cannot change during the lockout time period t established by lockout timer  719 . Noise present at the Hall sensor outputs H+, H− cannot change the commutation latch  715  state during the lockout timer  719  lockout time period t. 
     The outputs Q and Q′ of commutation latch  715  are combined with the PWM speed signal generated within controller  100  by gates  721  and  723  to provide motor commutation and PWM speed signals to drivers  315 ,  313 , respectively. 
     Controller  100  utilizes pulse width modulation to provide an energy efficient means for controlling the motor speed of fan motor  200  by varying the average applied voltage to each stator winding  203 ,  205  during the commutation sequence. 
     Direct motor drive is accomplished by providing two on-chip open drain N-channel MOSFETs  313 ,  315 , each having a high breakdown voltage. The respective MOSFET  313 ,  315  drains are pinned out to output terminals φ 1 , φ 2  for direct connection to motor windings  203 ,  205 . Zener and series diodes  314 ,  314   a  are connected from each respective MOSFET drain to gate to protect the MOSFETs  313 ,  315  from excessive inductive voltage spikes. 
     The invention has been described in conjunction with a specific illustrative embodiment. It will be understood by those skilled in the art that various changes, substitutions and modifications may be made without departing from the spirit or scope of the invention. It is intended that all such changes, substitutions and modifications be included in the scope of the invention. It is not intended that the invention be limited to the illustrative embodiment shown and described herein. It is intended that the invention be limited only by the claims appended hereto, giving the claims the broadest possible scope and coverage permitted under the law.