MC33030P データシートの表示（PDF） - Motorola => Freescale
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MC33030P Datasheet PDF : 16 Pages
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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
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.
+ + + tDLY
Vref CDLY
IDLY(source)
7.5 CDLY
5.5 µA
1.36 CDLY in µF
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.
This system allows the Power H–Switch to supply motor
start–up current for a predetermined amount of time. If the
MOTOROLA ANALOG IC DEVICE DATA
7
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