MC33030DWG View Datasheet(PDF) - ON Semiconductor

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Description

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MC33030DWG

DC Servo Motor Controller/Driver

ON Semiconductor 

MC33030

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

Detector (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

overridden 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 mA. 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 Overcurrent Monitor is designed to distinguish

between motor startup 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 overcurrent 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

overcurrent 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.

tDLY

+

Vref CDLY

IDLY(source)

+

7.5 CDLY

5.5 μA

+

1.36

CDLY

in μF

This system allows the Power H−Switch to supply motor

startup current for a predetermined amount of time. If the

rotor is locked, the system will time−out and shutdown. 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 overcurrent 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

overcurrent latch is reset upon powerup 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 Overvoltage 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

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