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| NJM37717 STEPPER MOTOR DRIVER s GENERAL DESCRIPTION NJM37717 is a stepper motor diver, which consists of a LS-TTL compatible logic input stage, a current sensor, a monostable multivibrator and a high power H-bridge output stage with built-in protection diodes. NJM37717 is a high voltage version and pin compatible with NJM3717. The output current is up to 1200mA. Two NJM37717 and a small number of external components from a complete control and drive unit for stepper moter system. s PACKAGE OUTLINE s FEATURES * Half-step and full-step modes * Switched mode bipolar constant current drive * Wide range of current control * Wide voltage range 10 - 60 V * Thermal overload protection * Packages DIP16 5 - 1200 mA s BLOCK DIAGRAM Figure 1. Block diagram NJM37717 s PIN CONFIGURATIONS Figure 2. Pin configurations s PIN DESCRIPTION DIP Symbol Description 1 2 3,14 4,5 12,13 6 7 8 9 10 11 15 16 MB T VMM GND Motor output B, Motor current flows from MA to MB when Phase is high. Clock oscillator. Timing pin connect a 56 k resistor and a 820 pF in parallel between T and Ground. Motor supply voltage, 10 to 56 V. VMM pins should be wired together on PCB. Ground and negative supply. Note these pins are used for heatsinking. Make sure that all ground pins are soldered onto a suitable large copper ground plane for efficient heat sinking. Logic voltage supply normally +5 V. Logic input, it controls, together with the I0 input, the current level in the output stage. The controllable levels are fixed to 100, 60, 20, 0%. Controls the direction of the motor current of MA and MB outputs. Motor current flows from MA to MB when the phase input is high. Logic input, it controls, together with the I1 input, the current level in the output stage. The controlable levels are fixed to 100, 60, 20, 0%. Comparator input. This input senses the instantaneous voltage across the sensing resistor, filtered through a RC Network. Reference voltage. Controls the threshold voltage of the comparator and hence the output current. Input resistance: typically 6.8k 20%. Motor output A, Motor current flows from MA to MB when Phase is high. Common emitter. Connect the sense resistor between this pin and ground. VCC I1 Phase I0 C VR MA E NJM37717 Figure 3. Definition of terms s FUNCTIONAL DESCRIPTION The NJM37717 is intended to drive a bipolar constant current through one motor winding of a 2-phase stepper motor. Current control is achieved through switched-mode regulation, see figure 4 and 5. Three different current levels and zero current can be selected by the input logic. The circuit contains the following functional blocks: * Input logic * Current sense * Single-pulse generator * Output stage Input logic Phase input. The phase input determines the direction of the current in the motor winding. High input forces the current from terminal MA to MB and low input from terminal MB to MA. A Schmitt trigger provides noise immunity and a delay circuit eliminates the risk of cross conduction in the output stage during a phase shift. Half- and full-step operation is possible. Current level selection. The status of I0 and I 1 inputs determines the current level in the motor winding. Three fixed current levels can be selected according to the table below. Motor current I0 I1 High level 100% L L Medium level 60% H L Low level 20% L H Zero current 0% H H The specific values of the different current levels are determined by the reference voltage VR together with the value of the sensing resistor RS. The peak motor current can be calculated as follows: im = (V R * 0.083) / RS [A], at 100% level im = (V R * 0.050) / RS [A], at 60% level im = (V R * 0.016) / RS [A], at 20% level The motor current can also be continuously varied by modulating the voltage reference input. NJM37717 Current sensor The current sensor contains a reference voltage divider and three comparators for measuring each of the selectable current levels. The motor current is sensed as a voltage drop across the current sensing resistor, RS, and compared with one of the voltage references from the divider. When the two voltages are equal, the comparator triggers the single-pulse generator. Only one comparator at a time is activated by the input logic. Single-pulse generator The pulse generator is a monostable multivibrator triggered on the positive edge of the comparator output. The multivibrator output is high during the pulse time, toff , which is determined by the timing components RT and CT. toff = 0.69 * RT * CT The single pulse switches off the power feed to the motor winding, causing the winding to decrease during toff.If a new trigger signal should occur during toff , it is ignored. Output stage The output stage contains four transistors and four diodes, connected in an H-bridge. The two sinking transistors are used to switch the power supplied to the motor winding, thus driving a constant current through the winding. See figures 4 and 5. Overload protection The circuit is equipped with a thermal shut-down function, which will limit the junction temperature. The output current will be reduced if the maximum permissible junction temperature is exceeded. It should be noted, however, that it is not short circuit protected. Operation When a voltage V MM is applied across the motor winding, the current rise follows the equation: im = (VMM / R) * (1 - e-(R * t ) / L ) R = Winding resistance L = Winding inductance t = time (see figure 5, arrow 1) The motor current appears across the external sensing resistor, RS, as an analog voltage. This voltage is fed through a low-pass filter, RCCC, to the voltage comparator input (pin 10). At the moment the sensed voltage rises above the comparator threshold voltage, the monostable is triggered and its output turns off the conducting sink transistor. The polarity across the motor winding reverses and the current is forced to circulate through the appropriate upper protection diode back through the source transistor (see figure 5, arrow 2). After the monostable has timed out, the current has decayed and the analog voltage across the sensing resistor is below the comparator threshold level. The sinking transistor then closes and the motor current starts to increase again, The cycle is repeated until the current is turned off via the logic inputs. By reversing the logic level of the phase input (pin 8), both active transistors are turned off and the opposite pair turned on after a slight delay. When this happens, the current must first decay to zero before it can reverse. This current decay is steeper because the motor current is now forced to circulate back through the power supply and the appropriate sinking transistor protection diode. This causes higher reverse voltage build-up across the winding which results in a faster current decay (see figure 5, arrow 3). For best speed performance of the stepper motor at half-step mode operation, the phase logic level should be changed at the same time the current-inhibiting signal is applied (see figure 6). NJM37717 Figure 4. Motor current (IM ), Vertical : 200 mA/div, Horizontal: 1 ms/div, expanded part 100 s/div Figure 5. Output stage with current paths for fast and slow current decay Figure 6. Principal operating sequence NJM37717 s ABSOLUTE MAXIMUM RATINGS (Ta=25C) Parameter Pin [DIP] Symbol Min Max Unit Voltage Logic supply Motor supply Logic inputs Comparator input Reference input Current Motor output current Logic inputs Analog inputs Temperature Operating junction temperature Storage temperature Tj Tstg -40 -55 +150 +150 C C 6 3, 14 7, 8, 9 10 11 1, 15 7, 8, 9 10, 11 VCC VMM VI VC VR IM II IA 0 0 -0.3 -0.3 -0.3 -1200 -10 -10 7 60 6 VCC 15 +1200 V V V V V mA mA mA s RECOMMENDED OPERATING CONDITIONS (Ta=25C) Parameter Symbol Min Typ Max Unit Logic supply voltage Motor supply voltage Motor output current Operating junction temperature Rise time logic inputs Fall time logic inputs VCC VMM IM Tj tr tf 4.75 10 -1000 -20 - 5 - 5.25 56 +1000 +125 2 2 V V mA C s s Figure7. Definition of symbols NJM37717 s ELECTRICAL CHARACTERISTICS Electrical characteristics over recommended operating conditions, unless otherwise specified .Ta=25C,CT = 820 pF, RT = 56k Parameter Symbol Conditions Min Typ Max Unit General Supply current Total power dissipation ICC PD fs = 28 kHz, IM = 500mA, VMM = 36 V Note 2, 4. fs = 28 kHz, IM = 800mA, VMM = 36 V Note 3, 4. dVC/dt 50 mV/s.VMM = 60 V,RL=200 VIH VIL IIH IIL RR VCH VCM VCL IC IM = 500 mA IM = 800 mA IM = 500 mA IM = 800 mA IM = 500 mA IM = 800 mA IM = 500 mA IM = 800 mA I0 = I1 = HIGH, Ta = +25C toff VMM = 10 V, ton 5 s VI = 2.4 V VI = 0.4 V Ta = +25C VR = 5.0 V, I0 = I1 = LOW VR = 5.0 V, I0 = HIGH, I1 = LOW VR = 5.0 V, I0 = LOW, I1 = HIGH 2.0 -0.4 400 240 70 -20 27 1.4 2.8 0.9 165 6.8 415 250 80 0.9 1.1 1.2 1.3 1.0 1.2 1.0 1.2 31 25 1.7 3.3 1.5 0.8 20 430 265 90 1.2 1.4 1.5 1.7 1.25 1.5 1.25 1.45 100 35 mA W W s C V V A mA k mV mV mV A V V V V V V V V A s Turn-off delay Thermal shutdown junction temperature Logic Inputs Logic HIGH input voltage Logic LOW input voltage Logic HIGH input current Logic LOW input current Reference Input Input resistance Comparator Inputs Threshold voltage Threshold voltage Threshold voltage Input current Motor Outputs Lower transistor saturation voltage Lower diode forward voltage drop Upper transistor saturation voltage Upper diode forward voltage drop Output leakage current Monostable Cut off time td s THERMAL CHARACTERISTICS Parameter Symbol Conditions Min Typ Max Unit Thermal resistance Rthj-GND DIP package. RthJ-A DIP package. Note 2. - 11 40 - C/W C/W Notes 1. All voltages are with respect to ground. Currents are positive into, negative out of specified terminal. 2. All ground pins soldered onto a 20 cm2 PCB copper area with free air convection. TA +25C. 3. DIP package with external heatsink (Staver V7) and minimal copper area. Typical RthJ-A = 27.5C/W. TA = +25C. 4. Not covered by final test program. NJM37717 s Applications Information Motor selection Some stepper motors are not designed for continuous operation at maximum current. As the circuit drives a constant current through the motor, its temperature can increase, both at low- and high-speed operation. Some stepper motors have such high core losses that they are not suited for switched-mode operation. Interference As the circuit operates with switched-mode current regulation, interference-generation problems can arise in some applications. A good measure is then to decouple the circuit with a 0.1 F ceramic capacitor, located near the package across the power line VMM and ground. Also make sure that the VR input is sufficiently decoupled. An electrolytic capacitor should be used in the +5 V rail, close to the circuit. The ground leads between RS, CC and circuit GND should be kept as short as possible. This applies also to the leads connecting RS and RC to pin 16 and pin 10 respectively. In order to minimize electromagnetic interference, it is recommended to route MA and MB leads in parallel on the printed circuit board directly to the terminal connector. The motor wires should be twisted in pairs, each phase separately, when installing the motor system. Unused inputs Unused inputs should be connected to proper voltage levels in order to obtain the highest possible noise immunity. Ramping A stepper motor is a synchronous motor and does not change its speed due to load variations. This means that the torque of the motor must be large enough to match the combined inertia of the motor and load for all operation modes. At speed changes, the requires torque increases by the square, and the required power by the cube of the speed change. Ramping, i.e., controlled acceleration or deceleration must then be considered to avoid motor pullout. VCC , VMM The supply voltages, V CC and V MM , can be turned on or off in any order. Normal dV/dt values are assumed. Before a driver circuit board is removed from its system, all supply voltages must be turned off to avoid destructive transients from being generated by the motor. Figure 8. Typical stepper motor driver application with NJM37717 NJM37717 Analog control As the current levels can be continuously controlled by modulating the V R input, limited microstepping can be achieved. Switching frequency The motor inductance, together with the pulse time, toff , determines the switching frequency of the current regulator. The choice of motor may then require other values on the R T , CT components than those recommended in figure7, to obtain a switching frequency above the audible range. Switching frequencies above 40 kHz are not recommended because the current regulation can be affected. Sensor resistor The RS resistor should be of a non-inductive type, power resistor. A 1.0 ohm resistor, tolerance 1%, is a good choice for 415 mA max motor current at VR = 5V. The peak motor current, im , can be calculated by using the formulas: im = (V R * 0.083) / RS [A], at 100% level im = (V R * 0.050) / RS [A], at 60% level im = (V R * 0.016) / RS [A], at 20% level Heatsinking The junction temperature of the chip highly effects the lifetime of the circuit. In high-current applications, the heatsinking must be carefully considered. The Rthj-a of the NJM37717 can be reduced by soldering the ground pins to a suitable copper ground plane on the printed circuit board (see figure 10) or by applying an external heatsink type V7 or V8, see figure 9. The diagram in figure 16 shows the maximum permissible power dissipation versus the ambient temperature in C, for heatsinks of the type V7, V8 or a 20 cm2 copper area respectively. Any external heatsink or printed circuit board copper must be connected to electrical ground. For motor currents higher than 500 mA, heatsinking is recommended to assure optimal reliability. The diagrams in figures 9 and 10 can be used to determine the required heatsink of the circuit. In some systems, forced-air cooling may be available to reduce the temperature rise of the circuit. Figure 9. Heatsinks, Staver, type V7 and V8 by Columbia-Staver UK Figure 10. Copper foil used as a heatsink NJM37717 s TYPICAL CHARACTERISTICS Figure 11. Typical source saturation vs. output current Figure 12. Typical sink saturation vs. output current Figure 13. Typical lower diode voltage drop vs. recirculating current Figure 14. Typical upper diode voltage drop vs. recirculating current Figure 15. Typical power dissipation vs. motor current Figure 16. Allowable power dissipation vs. ambient temperature The specifications on this databook are only given for information , without any guarantee as regards either mistakes or omissions. The application circuits in this databook are described only to show representative usages of the product and not intended for the guarantee or permission of any right including the industrial rights. |
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