7/95 half-step and full-step capability bipolar constant current motor drive built-in fast recovery schottky commutating diodes wide range of current control 5-1000ma wide voltage range 10-45v designed for unregulated motor supply voltage current levels can be selected in steps or varied continuously thermal overload protection stepper motor drive circuit the uc3717 h as been designed to control and drive the current in one winding of a bipolar stepper motor. the circuit consists of an ls- ttl-compatible logic input, a current sensor, a monostable and an output stage with built-in protection diodes. two uc3717s and a few external components fo rm a complete control and drive unit for ls- ttl or micro-processor controlled stepper motor systems. the uc1717 is characterized for operation over the full military tem - perature range of -55c to +125c, the uc2717 is characterized for -25c to +85c, and the uc3717 is characterized for 0c to +70c. uc1717 uc2717 uc3717 block diagram features description voltage logic supply, v cc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7v output supply, v m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45v input voltage logic inputs (pins 7, 8, 9). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6v analog input (pin 10) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vcc 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) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1a junction temperature, t j . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +150c storage temperature range, t s . . . . . . . . . . . . . . . . . . -55c to +150c absolute maximum ratings (note 1) note 1: all voltages are with respect to ground, pins 4,5, 12, 13. pin numbers refer to dil-16 package. cur- rents are positive into, negative out of the specified ter- minal. note 2: consult packaging section of databook for in- formation on thermal limitations and considerations of package.
uc1717 uc2717 uc3717 package pin function function pin n/c 1 b out 2 timing 3 v m 4 gnd 5 n/c 6 gnd 7 v cc 8 i 1 9 phase 10 n/c 11 i 0 12 current 13 v r 14 gnd 15 n/c 16 gnd 17 v m 18 a out 19 emitters 20 dil-16 (top view) j or n package connection diagrams electrical characteristics unless otherwise specified, these specifications apply for v cc = 5v, t a = t j . parameter min typ max units supply voltage, v cc 4.75 5 5.25 v supply voltage, v m 10 40 v output current. i m 20 800 ma rise time logic inputs, t r 2 m s fall time logic inputs, t f 2 m s ambient temperature, t a uc1717 -55 125 c uc2717 -25 85 c uc3717 0 70 c recommended operating conditions parameter test conditions min typ max units supply current, i cc 25 ma high-level input voltage, pins 7, 8, 9 2.0 v low-level input voltage, pins 7, 8, 9 0.8 v high-level input current, pins 7, 8, 9 v i = 2.4v 20 m a low level input current, pins 7, 8, 9 v i = 0.4v -0.4 ma comparator threshold voltage i o = 0, i 1 = 0, v r = 5.0v 390 420 440 mv i o = 1, i 1 = 0, v r = 5.0v 230 250 270 mv i o = 0, i 1 = 1, v r = 5.0v 65 80 90 mv comparator input current -20 20 m a output leakage current i o = 1, i 1 = 1, t a = +25c 100 m a total saturation voltage drop i m = 500ma 4.0 v total power dissipation i m = 500ma, f s = 30khz 1.4 2.1 w i m = 800ma, f s = 30khz 2.9 3.1 w cut off time, t off v m = 10v, t on 3 5 m s (see figure 5 and 6) 25 30 35 m s turn off delay, t d t a = +25c; dvc/dt 3 50mv/ m s (see figure 5 and 6) 1.6 2.0 m s thermal shutdown junction temperature +160 +180 c plcc-20 (top view) q package 2
figure 1 figure 3: typical sink saturation voltage vs output current figure 2: typical source saturation voltage vs output current figure 4: typical power losses vs output current uc1717 uc2717 uc3717 figure 5: connections and component values as in figure 6. the uc3717 drive circuit shown in the block diagram in- cludes the following functions: (1) phase logic and h-bridge output stage (2) voltage divider with three comparators for current control (3) two logic inputs for digital current level select (4) monostable for off time generation input logic: if any of the logic inputs are left open, the circuit will treat it as a high level input. phase input: the phase input terminal, pin 18, controls the direction of the current through the motor winding. the schmidt-trigger input coupled with a fixed time de- lay assures noise immunity and eliminates cross conduc- tion in the output stage during phase changes. a low level on the phase input will turn q2 on and enable q3 while a high level will turn q1 on and enable q4. (see figure 7). output stage: the output stage consists of four dar- lington transistors and associated diodes connected in an h-bridge configuration. the diodes are needed to pro- vide a current path when the transistors are being switched. for fast recovery, schottky diodes are used functional description across the source transistors. the schottky diodes allow the current to circulate through the winding while the sink transistors are being switched off. the diodes across the sink transistors in conjunction with the schottkys provide the path for the decaying current during phase reversal. (see figure 7). phase input q1, q4 q2, q3 low off on high on off 3
i 0 i 1 current level 0 0 100% 1 0 60% 0 1 19% 1 1 current inhibit current control: the voltage divider, comparators and monostable provide a means for current sensing and control. the two bit input (i 0 , i 1 ) logic selects the desired comparator. the monostable controls the off time and therefore the magnitude of the current decrease. the time duration is determined by r t and c t connected to the timing terminal (pin 2). the reference terminal (pin 11) provides a means of continuously varying the cur- rent for situations requiring half-stepping and micro- stepping. the relationship between the logic input signals at pin 7 and 9 in reference to the current level is shown in table 1. the values of the different current lev- els are determined by the reference voltage together with the value of the external sense resistor r s (pin 16). single-pulse generator: the pulse generator is a monostable triggered on the positive going edge of the comparator. its output is high during the pulse time and this pulse switches off the power feed to the motor wind- ing causing the current to decay. the time is determined by the external timing components r t and c t as: t off = 0.69 r t c t if a new trigger signal should occur during t off , it is ig- nored. figure 6 figure 7: simplified schematic of output stage uc1717 uc2717 uc3717 note: dashed lines indicate current decay paths. 4
overload protection: the circuit is equipped with a thermal shutdown function, which will limit the junction temperature by reducing the output current. it should be noted however, that a short circuit of the output is not permitted. operation: when the voltage is applied across the motor winding the current rises linearly and appears across the external sense resistor as an analog voltage. this volt- age is fed through a low pass filter r c , c c to the voltage comparator (pin 10). at the moment the voltage rises be- yond the comparator threshold voltage the monostable is triggered and its output turns off the sink transistors. the current then circulates through the source transistor and the appropriate schottky diode. after the one shot has timed out, the sink transistsor is turned on again and the procedure repeated until a current reverse command is given. by reversing the logic level of the phase input (pin 8), both active transistors are being turned off and the opposite pair turned on. when this happens the current must first decay to zero before it can reverse. the cur- rent path then provided is through the two diodes and the power-supply. refer to figure 7. it should be noted at this time that the slope of the current decay is steeper, and this is due to the higher voltage build up across the winding. for better speed performance of the stepping motor at half step mode, the phase logic level should be changed at the same time the current inhibit is applied. a typical current wave form is shown in figure 8. applications a typical chopper drive for a two phase bipolar perma- nent magnet or hybrid stepping motor is shown in figure 9. the input can be controlled by a microprocessor, ttl, ls or cmos logic. the timing diagram in figure 10 shows the required sig- nal input for a two phase, full step, stepping sequence. figure 11 shows a one phase, full step, stepping se- quence, commonly referred to as wave drive. figure 12 shows the required input signal for a one phase-two phase stepping sequence called half-stepping. the circuit of figure 13 provides the signal shown in fig- ure 10, and in conjunction with the circuit shown in fig- ure 9, will implement a pulse-to-step two phase, full step, bidirectional motor drive. the schematic of figure 14 shows a pulse to half step circuit generating the signal shown in figure 12. care has been taken to change the phase signal the same time the current inhibit is applied. this will allow the cur- rent to decay faster and therefore enhance the motor performance at higher step rates. using the uc3717 to drive the l298 provides a uniquely packaged state-of-the-art high power stepper motor con- trol and drive. see figure 15. figure 8 functional description (cont.) figure 9 uc1717 uc2717 uc3717 5
functional description (cont.) figure 10: phase input signal for two phase full step drive (4 step sequence) figure 11: phase and current-inhibit signal for wave drive (4 step sequence) uc1717 uc2717 uc3717 figure 12: phase and current-inhibit signal for half stepping (8 step sequence) figure 13: full step bidirectional two phase drive logic 6
uc1717 uc2717 uc3717 figure 14: half-step, bidirectional drive logic half-stepping: in the half step sequence the power in- put to the motor alternates between one or two phases being energized. in a two phase motor the electrical phase shift between the windings is 90 degrees. 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 r input can be used to boost the current of the single energized winding. ramping: every drive system has inertia and must be considered in the drive scheme. the rotor and load iner- tia plays a big role at higher speeds. unlike the dc motor the stepping motor is a synchronous motor and does not change its speed due to load variations. examining typi- cal stepping motors, torque vs. speed curves indicates a sharp torque drop off for the start-stop without error curve, even with a constant current drive. the reason for this is that the torque requirements increase by the square of the speed change, and the power need in- creases by the cube of the speed change. as it can be seen, for good motor performance controlled accelera- tion and deceleration should be considered. iron core lo sses: some motors, especially the tin-can type, exhibit high iron losses mostly due to eddy currents which rise in an exponential manner as the frequency or step rate is increased. the power losses can not be cal- culated by i 2 r where i is the chopping current level and r the dc resistance of the coil. actual measurements in- dicate the effective resistance may be many times larger. therefore, for 100% duty cycle the current must be lim- ited to a value which will not overheat the motor. this may not be necessary for lower duty cycle operation. interference: electrical noise generated by the chopping action can cause interference problems, particularly in the vicinity of magnetic storage media. with this in mind, printed circuit layouts, wire runs and decoupling must be considered. 0.01 to 0.1 m f ceramic capacitors for high fre- quency 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. ordering information unitrode type number uc3717n - 16 pin dual-in-line (dil) "bat wing" package uc1717j - 16 pin dual-in-line ceramic package uc1717sp - 16 pin dual-in-line hermetic power package consideration 7
unitrode integrated circuits 7 continental blvd. merrimack, nh 03054 tel. (603) 424-2410 fax (603)424-3460 uc1717 uc2717 uc3717 figure 15: uc3717 with l298 power amplifier 8
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