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MC33033P Scheda tecnica(PDF) 9 Page - ON Semiconductor |
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MC33033P Scheda tecnica(HTML) 9 Page - ON Semiconductor |
9 / 24 page MC33033 9 MOTOROLA ANALOG IC DEVICE DATA INTRODUCTION The MC33033 is one of a series of high performance monolithic dc brushless motor controllers produced by Motorola. It contains all of the functions required to implement a limited–feature, open loop, three or four phase motor control system. Constructed with Bipolar Analog technology, it offers a high degree of performance and ruggedness in hostile industrial environments.The MC33033 contains a rotor position decoder for proper commutation sequencing, a temperature compensated reference capable of supplying sensor power, a frequency programmable sawtooth oscillator, a fully accessible error amplifier, a pulse width modulator comparator, three open collector top drive outputs, and three high current totem pole bottom driver outputs ideally suited for driving power MOSFETs. Included in the MC33033 are protective features consisting of undervoltage lockout, cycle–by–cycle current limiting with a latched shutdown mode, and internal thermal shutdown. Typical motor control functions include open loop speed control, forward or reverse rotation, and run enable. In addition, the MC33033 has a 60 °/120° select pin which configures the rotor position decoder for either 60 ° or 120° sensor electrical phasing inputs. FUNCTIONAL DESCRIPTION A representative internal block diagram is shown in Figure 18, with various applications shown in Figures 34, 36, 37, 41, 43, and 44. A discussion of the features and function of each of the internal blocks given below and referenced to Figures 18 and 36. Rotor Position Decoder An internal rotor position decoder monitors the three sensor inputs (Pins 4, 5, 6) to provide the proper sequencing of the top and bottom drive outputs. The Sensor Inputs are designed to interface directly with open collector type Hall Effect switches or opto slotted couplers. Internal pull–up resistors are included to minimize the required number of external components. The inputs are TTL compatible, with their thresholds typically at 2.2 V. The MC33033 series is designed to control three phase motors and operate with four of the most common conventions of sensor phasing. A 60 °/120° Select (Pin 18) is conveniently provided which affords the MC33033 to configure itself to control motors having either 60 °, 120°, 240° or 300° electrical sensor phasing. With three Sensor Inputs there are eight possible input code combinations, six of which are valid rotor positions. The remaining two codes are invalid and are usually caused by an open or shorted sensor line. With six valid input codes, the decoder can resolve the motor rotor position to within a window of 60 electrical degrees. The Forward/Reverse input (Pin 3) is used to change the direction of motor rotation by reversing the voltage across the stator winding. When the input changes state, from high to low with a given sensor input code (for example 100), the enabled top and bottom drive outputs with the same alpha designation are exchanged (AT to AB, BT to BB, CT to CB). In effect the commutation sequence is reversed and the motor changes directional rotation. Motor on/off control is accomplished by the Output Enable (Pin19). When left disconnected, an internal pull–up resistor to a positive source enables sequencing of the top and bottom drive outputs. When grounded, the Top Drive Outputs turn off and the bottom drives are forced low, causing the motor to coast. The commutation logic truth table is shown in Figure 19. In half wave motor drive applications, the Top Drive Outputs are not required and are typically left disconnected. Error Amplifier A high performance, fully compensated Error Amplifier with access to both inputs and output (Pins 9, 10, 11) is provided to facilitate the implementation of closed loop motor speed control. The amplifier features a typical dc voltage gain of 80 dB, 0.6 MHz gain bandwidth, and a wide input common mode voltage range that extends from ground to Vref. In most open loop speed control applications, the amplifier is configured as a unity gain voltage follower with the Noninverting Input connected to the speed set voltage source. Additional configurations are shown in Figures 29 through 33. Oscillator The frequency of the internal ramp oscillator is programmed by the values selected for timing components RT and CT. Capacitor CT is charged from the Reference Output (Pin 7) through resistor RT and discharged by an internal discharge transistor. The ramp peak and valley voltages are typically 4.1 V and 1.5 V 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. Refer to Figure 1 for component selection. Pulse Width Modulator The use of pulse width modulation 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 CT discharges, the oscillator sets both latches, allowing conduction of the Top and Bottom Drive Outputs. The PWM comparator resets the upper latch, terminating the Bottom Drive Output conduction when the positive–going ramp of CT becomes greater than the Error Amplifier output. The pulse width modulator timing diagram is shown in Figure 20. Pulse width modulation for speed control appears only at the Bottom Drive Outputs. Current Limit Continuous operation of a motor that is severely over–loaded results in overheating and eventual failure. This destructive condition can best be prevented with the use of cycle–by–cycle current limiting. That is, each on–cycle is treated as a separate event. Cycle–by–cycle current limiting is accomplished by monitoring the stator current build–up each time an output switch conducts, and upon sensing an over current condition, immediately turning off the switch and holding it off for the remaining duration of |
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