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MC33030 датащи(PDF) 7 Page - ON Semiconductor |
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MC33030 датащи(HTML) 7 Page - ON Semiconductor |
7 / 16 page MC33030 7 MOTOROLA ANALOG IC DEVICE DATA OPERATING DESCRIPTION The MC33030 was designed to drive fractional horsepower DC motors and sense actuator position by voltage feedback. A typical servo application and representative internal block diagram are shown in Figure 17. The system operates by setting a voltage on the reference input of the Window Dectector (Pin 1) which appears on (Pin 2). A DC motor then drives a position sensor, usually a potentiometer driven by a gear box, in a corrective fashion so that a voltage proportional to position is present at Pin 3. The servo motor will continue to run until the voltage at Pin 3 falls within the dead zone, which is centered about the reference voltage. The Window Detector is composed of two comparators, A and B, each containing hysteresis. The reference input, common to both comparators, is pre–biased at 1/2 VCC for simple two position servo systems and can easily be overriden by an external voltage divider. The feedback voltage present at Pin 3 is connected to the center of two resistors that are driven by an equal magnitude current source and sink. This generates an offset voltage at the input of each comparator which is centered about Pin 3 that can float virtually from VCC to ground. The sum of the upper and lower offset voltages is defined as the window detector input dead zone range. To increase system flexibility, an on–chip Error Amp is provided. It can be used to buffer and/or gain–up the actuator position voltage which has the effect of narrowing the dead zone range. A PNP differential input stage is provided so that the input common–mode voltage range will include ground. The main design goal of the error amp output stage was to be able to drive the window detector input. It typically can source 1.8 mA and sink 250 µA. Special design considerations must be made if it is to be used for other applications. The Power H–Switch provides a direct means for motor drive and braking with a maximum source, sink, and brake current of 1.0 A continuous. Maximum package power dissipation limits must be observed. Refer to Figure 15 for thermal information. For greater drive current requirements, a method for buffering that maintains all the system features is shown in Figure 30. The Over–Current Monitor is designed to distinguish between motor start–up or locked rotor conditions that can occur when the actuator has reached its travel limit. A fraction of the Power H–Switch source current is internally fed into one of the two inverting inputs of the current comparator, while the non–inverting input is driven by a programmable current reference. This reference level is controlled by the resistance value selected for ROC, and must be greater than the required motor run–current with its mechanical load over temperature; refer to Figure 8. During an over–current condition, the comparator will turn off and allow the current source to charge the delay capacitor, CDLY. When CDLY charges to a level of 7.5 V, the set input of the over–current latch will go high, disabling the drive and brake functions of the Power H–Switch. The programmable time delay is determined by the capacitance value–selected for CDLY. t DLY + V ref C DLY I DLY(source) + 7.5 C DLY 5.5 µA + 1.36 C DLY in µF This system allows the Power H–Switch to supply motor start–up current for a predetermined amount of time. If the rotor is locked, the system will time–out and shut–down. This feature eliminates the need for servo end–of–travel or limit switches. Care must be taken so as not to select too large of a capacitance value for CDLY. An over–current condition for an excessively long time–out period can cause the integrated circuit to overheat and eventually fail. Again, the maximum package power dissipation limits must be observed. The over–current latch is reset upon power–up or by readjusting VPin 2 as to cause VPin 3 to enter or pass through the dead zone. This can be achieved by requesting the motor to reverse direction. An Over–Voltage Monitor circuit provides protection for the integrated circuit and motor by disabling the Power H–Switch functions if VCC should exceed 18 V. Resumption of normal operation will commence when VCC falls below 17.4 V. A timing diagram that depicts the operation of the Drive/Brake Logic section is shown in Figure 18. The waveforms grouped in [1] show a reference voltage that was preset, appearing on Pin 2, which corresponds to the desired actuator position. The true actuator position is represented by the voltage on Pin 3. The points V1 through V4 represent the input voltage thresholds of comparators A and B that cause a change in their respective output state. They are defined as follows: V1 = Comparator B turn–off threshold V2 = Comparator A turn–on threshold V3 = Comparator A turn–off threshold V4 = Comparator B turn–on threshold V1–V4 = Comparator B input hysteresis voltage V2–V3 = Comparator A input hysteresis voltage V2–V4 = Window detector input dead zone range |(V2–VPin2) – (VPin2 – V4)| = Window detector input voltage It must be remembered that points V1 through V4 always try to follow and center about the reference voltage setting if it is within the input common–mode voltage range of Pin 3; Figures 4 and 5. Initially consider that the feedback input voltage level is somewhere on the dashed line between V2 and V4 in [1]. This is within the dead zone range as defined above and the motor will be off. Now if the reference voltage is raised so that VPin 3 is less than V4, comparator B will turn–on [3] enabling Q Drive, causing Drive Output A to sink and B to source motor current [8]. The actuator will move in Direction B until VPin 3 becomes greater than V1. Comparator B will turn–off, activating the brake enable [4] and Q Brake [6] causing Drive Output A to go high and B to go into a high impedance state. The inertia of the mechanical system will drive the motor as a generator creating a positive voltage on Pin 10 with respect to Pin 14. The servo system can be stopped quickly, so as not to over–shoot through the dead zone range, by braking. This is accomplished by shorting the motor/generator terminals together. Brake current will flow into the diode at Drive Output B, through the internal VCC rail, and out the emitter of the sourcing transistor at Drive Output A. The end of the solid line and beginning of the dashed for VPin 3 [1] indicates the possible resting position of the actuator after braking. |
Аналогичный номер детали - MC33030 |
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Аналогичное описание - MC33030 |
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