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查询UC3717A供应商
Stepper Motor Drive Circuit
FEATURES DESCRIPTION
• Full-Step, Half-Step and Micro-Step
Capability
• Bipolar Output Current up to 1A
• Wide Range of Motor Supply Voltage
10-46V
• Low Saturation Voltage with Integrated
Bootstrap
• Built-In Fast Recovery Commutating
Diodes
• Current Levels Selected in Steps or Varied
Continuously
• Thermal Protection with Soft Intervention
ABSOLUTE MAXIMUM RATINGS (Note 1)
Voltage
Logic Supply, VCC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7V
Output Supply, Vm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50V
Input Voltage
Logic Inputs (Pins 7, 8, 9) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6V
Analog Input (Pin 10). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V
Reference Input (Pin 11) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15V
Input Current
Logic Inputs (Pins 7, 8, 9) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -10mA
Analog Inputs (Pins 10, 11). . . . . . . . . . . . . . . . . . . . . . . . . . . . -10mA
Output Current (Pins 1, 15) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±1.2A
Junction Temperature, TJ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +150°C
Storage Temperature Range, TS. . . . . . . . . . . . . . . . . . -55°C to +150°C
The UC3717A is an impro ved ver sion of the UC3717, us ed to switch
drive the current in one winding of a bipolar stepper motor. The
UC3717A has been modified to supply higher winding current, more
reliable thermal protection, and improved efficiency by providing integrated bootstrap circuitry to lower recirculation saturation voltages.
The diagram shown below presents the building blocks of the
UC3717A. Includ ed are an LS-TTL compatible l ogic input, a current
sensor, a monostable, a ther mal shutd ow n netw ork, and an H-bri dge
output stage. The output stage features built-in fast recovery commutating diodes and integrated bootstrap pull up. Two UC3717As
and a few external components form a complete control and drive
unit for LS-TTL or micro-processor controlled stepper motor systems.
The UC3717A is characterized for operation over the temperature
range of 0°C to +70°C.
CC
UC3717A
Note 1: All voltages are with respect to ground, Pins 4,
5, 12, 13. Currents are positive into, negative out of the
specified terminal. Pin numbers refer to DIL-16 package.
Consult Packaging Section of Databook for thermal limitations and considerations of package.
BLOCK DIAGRAM
4/97
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CONNECTION DIAGRAMS
UC3717A
DIL-16 (TOP VIEW)
J or N Package
ELECTRICAL CHARACTERISTICS
PLCC-20 (TOP VIEW)
Q Package
(Refer to the te st c irc ui t, F ig ure 6 . Vm = 36V, VCC = 5V, VR = 5V, TA = 0°C to 70°C,
PACKAGE PIN FUNCTION
FUNCTION PIN
N/C
B
OUT
Timing
m
V
Gnd
N/C
Gnd
V
CC
I
1
Phase
N/C
I
0
Current
V
R
Gnd
N/C
Gnd
m
V
A
OUT
Emitters
unless otherwis e stat ed , TA = TJ.)
PARAMETERS TEST CONDITIONS MIN TYP MAX UNITS
Supply Voltage, Vm (Pins 3, 14) 10 46 V
Logic Supply Voltage, V
Logic Supply Current, I
(Pin 6) 4.75 5.25 V
CC
(Pin 6) IO = I1 = 0 7 15 mA
CC
Thermal Shutdown Temperature +160 +180 °C
Logic Inputs
Input Low Voltage, (Pins 7, 8, 9) 0.8 V
Input High Voltage, (Pins 7, 8, 9) 2 V
Low Voltage Input Current, (Pins 7, 8, 9) V
High Voltage Input Current, (Pins 7, 8, 9) V
= 0.4V, Pin 8 -100
I
V
= 0.4V, Pins 7 and 9 -400 mA
I
= 2.4V 10
I
CC
Comparators
Comparator Low, Thres ho ld Volt ag e (Pin 10) V
Comparator Medium, Threshold Voltage (Pin 10) V
Comparator High, Thre sh ol d Vol tage (Pin 10) V
Comparator Input, Current (Pin 10)
Cutoff Time, t
Turn Off Dela y, t
OFF
D
= 5V; IO = L; I1 = H 668090mV
R
= 5V; IO = H; I1 = L 236 250 266 mV
R
= 5V; IO = L; I1 = L 396 420 436 mV
R
20
±
RT = 56kΩ, CT = 820pF 25 35
(See Figure 5) 2
Source Diode-Transistor Pair
Saturation Voltage, V
(See Figure 5) I
Saturation Voltage, V
(See Figure 5) I
Leakage Current V
Diode Forward Voltage, V
(Pins 1, 15) Im = -0.5A, Conduction Period 1.7 2.1 V
SAT
= -0.5A, Recirculation Period 1.1 1.35 V
m
(Pins 1, 15) Im = -1A, Conduction Period 2.1 2.8 V
SAT
= -1A, Recirculation Period 1.7 2.5 V
m
= 40V 300
m
F
Im = -0.5A 1 1.25 V
I
= -1A 1.3 1.7 V
m
10
11
12
13
14
15
16
17
18
19
20
1
2
3
4
5
6
7
8
9
V
A
µ
A
µ
A
µ
s
µ
s
µ
A
µ
2
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UC3717A
ELECTRICAL
CHARACTERISTICS (cont.)
PARAMETERS TEST CONDITIONS MIN TYP MAX UNITS
Sink Diode-Transistor Pair
Saturation Voltage, V
Leakage Current V
Diode Forward Voltage, V
(Pins 1, 15) Im = 0.5A 0.8 1.1 1.35 V
SAT
F
(Refer to the te st c irc ui t, F ig ure 6 . VM = 36V, VCC = 5V, VR = 5V, TA = 0°C to 70°C, unless
otherwise stated, TA = TJ.)
I
= 1A 1.6 2.3 V
m
= 40V 300
m
Im = 0.5A 1.1 1.5 V
= 1A 1.4 2 V
I
m
µ
A
Figure 1. Typical Source Saturation Voltage
vs Output Current (Recirculation Period)
Figure 3. Typical Sink Saturation
Voltage vs Output Current
Figure 2. Typical Source Saturation Voltage
vs Output Current (Conduction Period)
Figure 4. Typical Power Dissipation
vs Output Current
Figure 5. Typical Waveforms with MA Regulating
(phase = 0)
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UC3717A
Figure 6. UC3717A Test Circuit
FUNCTIONAL DESCRIPTION
The UC3717A’s drive circuit shown in the block diagram
includes the following components.
(1) H-bridge output stage
(2) Phase polarity logic
(3) Voltage divider coupled with current sensing compa rators
(4) Two-bit D/A current level select
(5) Monostable generating fixed off-time
(6) Thermal protection
OUTPUT STAGE
The UC3717A’s output stage consists of four Darlington
power trans i s to rs an d a s s oci a te d r e c i rc ul a ti n g power diodes in a full H-bridge configuration as shown in Figure
7. Also presented, is the new added feature of inte-
grated bootstrap pull up, which improves device performance during switched mode operation. While in
switched mode, with a low level phase polarity input, Q2
is on and Q3 is being switched. At the moment Q3 turns
off, winding current begins to decay through the commutating di ode pu lling the collector of Q3 above the supply
voltage. Meanwhile, Q6 turns on pulling the base of Q2
higher than its previ ous val ue. The net effect lowers the
saturation voltage of source transistor Q2 during recirculation, thus improving efficiency by reducing power dissipation.
Note: Dashed lines indicate current decay paths.
Figure 7. Simplified Schematic of Output Stage
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FUNCTIONAL DESCRIPTION (cont.)
PHASE POLARITY INPUT
The UC3717A phase polarity input controls current direction in the motor winding. Built-in hysteresis insures immunity to noise, something frequently present in
switched drive environments. A low level phase polarity
input enables Q 2 and Q3 as shown in Figure 7. During
phase revers al, the act ive transis tors are both turned off
while winding current delays through the commutating diodes shown. As winding current decays to zero, the inactive transistors Q1 and Q4 turn on and charge the
winding with current of the reverse direction. This delay
insures n oise immunity a nd freedom from power supply
current spikes caused by overlapping drive signals.
PHASE INPUT Q1, Q4 Q2, Q3
LOW OFF ON
HIGH ON OFF
CURRENT CONTROL
The voltage div ider, comparators, monostable, and twobit D/A provide a me ans to sen se winding pe ak current,
select win di n g peak current, and disabl e the windi ng si nk
transistors.
The UC3717A switched driver accomplishes current control using an algorithm referred to as "fixed off-time."
When a vol tage is applied across the motor winding, the
current through the winding increases exponentially. The
current can be sensed across an external resistor as an
analog voltage proportional to instantaneous current.
This voltage is normally filtered with a simple R
low-
C
pass network to remove high frequency transients, and
then compared to one of the three selectable threshol ds.
The two bit D/ A input signal de termi nes wh ich on e of the
three thres holds is selected, c orresponding to a desired
winding peak current level. At the moment the sense voltage rises above the selected threshold, the UC3717A’s
monostable is triggered and disables both output sink
drivers fo r a fixed o ff-time. The w inding current then circulates th rough t he sourc e transistor and appropriate diode. The re ference termin al of the UC3717A provides a
means of conti nuously adj usting th e current threshold to
allow microstepping. Table 1 presents the relationship
between the t wo-bit D/A input signa l and selectable current level.
UC3717A
ture to a maximum of 180C by reducing the windi ng current.
PERFORMANCE CONSIDERATIONS
In order to achieve optimum performance from the
UC3717A careful atten tion s houl d be given to the following items.
External Components:
mal number of ex ternal compone nts to form a complete
control and switch drive unit. However, proper selection
of external components is necessary for optimum performance. The timing pin, (pin 2) is normally connected
to an RC network which sets the off-time for the sink
power trans istor during switc hed mode. As shown in Figure 8, prior to switched mode, the winding current increases exponentially to a peak value. Once peak
current is attained the monostable is triggered which
turns off the lo wer sink drivers for a fixed off-time. During
off-time windi ng current decays through the appropriate
diode and sou rce transistor. The moment off-time times
out, the motor current agai n rises exponentially producing the ripple waveform shown. The mag nitude of winding ripple is a direct function of off-time. For a given
off-time T
, the values of RT and CT can be calculated
OFF
from the expression:
T
with the r estrict ion that RT should be in the ra nge of 10100k. As s h ow n i n Fi gu r e 5, t he s witc h frequency F
function of T
and TON. Since TON is a function of the
OFF
reference voltage, sense resistor, motor supply, and
winding e lectrical c haracteristics, it generally v aries during different modes of operation. Thus, F
proximated nominally as:
Normally, Switch Frequency Is Selected Greater than
The UC3717A requires a mini-
0.69
=
OFF
F
1
⁄
=
S
1.5
RTC
(
T
OFF
T
may be ap-
S
).
is a
S
TABLE 1
O
I
0 0 100%
10 60%
01 19%
1 1 Current Inhibit
1
I
CURRENT LEVEL
OVERLOAD PROTECTION
The UC3717A is equipped with a new, more reliable thermal shutdown circuit which limits the junction tempera-
Figure 8. A typical winding current waveform. Winding current rises exponentially to a selected peak
value. The peak value is limited by switched mode
operation producing a ripple in winding current. A
phase polarity reversal comma nd is given and winding current decays to zero, then increases exponentially.
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FUNCTIONAL DESCRIPTION (cont.)
Low-pass filter components RC CC should be selected so
that all switching transients from the power transistors
and commutating diodes are well smoothed, but the primary signal, which can be in the range of 1/T
OFF
or
higher must be passed. Figure 5A shows the waveform
which must be smoothed, Figure 5B presents the desired
waveform that just smoothes out overshoot without radical distortion.
The sense resistor should be chosen as small as practical to allo w as much of the winding supply voltage to be
used as overd rive to the motor winding. V
, the voltage
RS
across the sense resistor, should not exceed 1.5V.
Voltage Overdrive:
In many applications, maximum
speed or step rate is a desirable performance characteristic. Maximum step rate is a direct function of the time
necessary to reverse w inding current with each step. In
response to a constant motor supply voltage, the winding
current chan ges exponentially with time, whos e shape is
determined b y the windi ng time constant and expressed
as:
m
I
=
m
R [1−EXP
V
(
T
−
R
⁄
]
)
L
as present ed in Figure 9 . Wit h rated v oltage applied, the
time required to reach rated current is excessive when
compared with the time required with over-voltage applied, even though the time constant L/R remains constant. With over-voltage however, the final value of
UC3717A
current is excessive and must be prevented. This is accomplishe d w ith swi tch driv e by repetitivel y switc hing the
sink drivers on and off, so as to maintain an average
value of cur rent equal to the rated value. This results in a
small amount of r ipple in the controlled current, but the
increase in s tep rate and pe rformance may be considerable.
Interference:
action can cause interference problems, particularly in
the vicini ty of magnetic storage media. With this in mind,
printed ci rcuit layouts, wire runs and dec oupling must be
considered. 0.01 to 0.1µF ceramic capacitors for h igh fr equency bypass located near the drive package across
V+ and ground might be very helpful. The connection
and ground leads of the current sensing components
should be kept as short as possible.
Half-Stepping:
the motor alternates between one or two phases being
energized. In a two phase motor the electrical phase shift
between the windings is 90°. The torque developed is the
vector sum of the two windings energized. Therefore
when only one winding is energized the torque of the motor is reduced by approximately 30%. This causes a
torque ripple and if it is necessary to compensate for this,
the V
input can be used to boost the current of the sin-
R
gle energized winding.
Electrical noise gener ated by the chopping
In half step seq uence the power input to
Figure 9. With rated vol tage applied, winding current does not exceed rated value, but takes L/R seconds to
reach 63% of its final value - probably too long. Increased performance requires an increase in applied voltage, of overdrive, and therefore a m eans to limit current. The UC3717A motor driver performs this task efficiently.
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MOUNTING INSTRUCTIONS
The θJA of the UC3717AN plastic package can be reduced by soldering the GND pins to a suitable copper
area of the printed circuit board or to an external heat
sink. Due to different lead frame design, θ
of the ce-
JA
ramic J package cannot be similarly reduced.
The diagram of Figure 11 shows the maximum package
power P
and the θJA as a function of the side " l " of
TOT
two equal square copper areas having a thickness of 35µ
(see Figure 10).
UC3717A
12. The input can be controlled by a microprocessor,
TTL, LS, or CMOS logic.
The timing di agram in Fig ure 13 sho ws the required signal input for a two phase, full step stepping sequence.
Figure 14 shows the required input signal for a one
phase-two phase stepping sequence called half-stepping.
The circuit of Figure 15 prov ides the signal shown i n Figure 13, and in conjunction with the circuit shown in Figure 12 will implement a pulse-to-step two phase, full
step, bi-directional motor drive.
Figure 10. Example of P.C. Board Copper
Area which is used as Heatsink.
During soldering the pins’ temperature must not exceed
260°C and t he s o l de r i ng t i me must not be l onger than 12
seconds.
The printed circuit copper area must be connected to
electrical ground.
Figure 11. Maximum Package Power and Junction
to Ambient Thermal Resistance vs Side "
l
".
APPLICATIONS
A typical chopper drive for a two phase bipolar permanent magnet or hybrid stepping motor is shown in Figure
Figure 12. Typical Chopper Drive for a Two
Phase Permanent Magnet Motor.
The schemati c of Figure 16 shows a pulse to half step
circuit generating the signal shown in Figure 14. Care
has been taken to change the phase signal the same
time the cur rent inhi bit is a pplied . This will allow the cur rent to decay faster and therefore enhance the motor
performance at high step rates.
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Figure 13. Phase Input Signal for Two Phase Full Step Drive (4 Step Sequence)
UC3717A
Figure 14. Phase and Current-Inhibit Signal for Half-Stepping (8 Step Sequence)
Figure 15. Full Step, Bi-directional Two Phase Drive Logic
UNITRODE CORPORATI ON
7 CONTINENTAL BLVD. • MERRIMACK, NH 03054
TEL. (603) 424- 24 10 • FAX (603) 424-3460
Figure 16. Half-Step, Bi-directional Drive Logic
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