NJM3770A STEPPER MOTOR DRIVER ■ GENERAL DESCRIPTION NJM3770A is a stepper motor driver, which consists of a LS-TTL compatible logic input stage, a current sensor, a monostable multivibrator and a high power H-bridge output stage. The NJM3770A is a high power version and pincompatible with the NJM3717.Two NJM3770A and a small number of external components form a complete control and drive unit stepper motor systems. ■ PACKAGE OUTLINE NJM3770AD3 NJM3770AE2 ■ EATURES • Half-step and full-step operation NJM3770AFM2 • Switched mode bipolar constant current drive • Wide range of current control 5 -1800 mA • Wide voltage range 10 - 45 V • Thermal overload protection • Packages DIP16 (Batwing) / PLCC28 / EMP20 ■ BLOCK DIAGRAM VMM VCC Schmitt Trigger VMM Time Delay Phase 1 ≥1 ≥1 I MA 1 MB I0 V R & & & ≥1 & + – ≥1 Output Stage + – Monostable t off = 0.69 • RT • CT + – GND Current Sensor NJM3770A C Figure 1. Block diagram T E NJM3770A GND GND 6 GND NJM 3770AE2 7 15 GND 14 GND GND 4 GND 5 14 VMM NJM 3770AD3 N/C 5 25 N/C MA 6 13 GND 24 V R N/C 7 12 GND 23 C NJM 3770AFM2 E 8 GND 9 22 N/C 21 I 0 M B 10 VCC 6 11 V R VCC 8 13 VR I1 9 12 C I1 7 10 C 11 I0 Phase 8 9 I0 Phase 10 26 N/C 16 GND 5 VMM 3 27 N/C GND 20 Phase T 11 19 I1 V CC 18 17 GND 17 GND 4 15 M A T 2 1 GND VMM 28 GND 18 GND 16 VMM 3 2 GND MA GND 15 19 GND 14 T 2 16 E V MM 12 E GND 13 20 4 V MM MB 1 MB 1 3 GND ■ PIN CONFIGURATIONS Figure 2. Pin configurations ■ PIN DESCRIPTION EMP DIP PLCC Symbol 1 2 1 2 10 11 MB T 3 3,14 12,4 VMM 4-7, 14-18 4,5, 12,13 1-3,9, 13-17,28 GND 8 9 6 7 18 19 VCC I1 10 8 20 Phase 11 9 21 I0 12 10 23 C 13 11 24 VR 19 20 15 16 6 8 MA E Description Motor output B, Motor current flows from MA to MB when Phase is high. Clock oscillator. Timing pin connect a 56 kΩ resistor and a 820 pF in parallel between T and Ground. Motor supply voltage, 10 to 40 V. Pin 3(12) and pin 14(4) should be wired to gether. 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 controllable 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 6.8 kΩ ± 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. NJM3770A ■ FUNCTIONAL DESCRIPTION The NJM3770A is intended to drive a bipolar constant current through one winding of a 2-phase stepper motor. Current control is achieved through switched-mode regulation, see figure 3 and 4. 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. External recirculation diodes 2 1 3 R 200 mA/div 1 ms/div S Motor Current 0 1 2 Fast Current Decay 3 100µs/div Time Slow Current Decay Figure 3. Output stage with current paths for fast and slow current decay. Figure 4. Motor current (IM ), Vertical : 200 mA/div, Horizontal: 1 ms/div, expanded part 100 µs/div. NJM3770A Current level selection. The status of I0 and I1 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 L L 100% Medium level 60% H L Low level L 20% Zero current 0% H 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 = (VR • 0.080) / RS [A], at 100% level The motor current can also be continuously varied by modulating the voltage reference input. 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 two diodes, connected in an H-bridge. Note that the upper recirculation diodes are connected to the circuit externally. 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 3 and 4. 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 VMM 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 3, 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 3, 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 turns on and the motor current starts to increase again, The cycle is repeated until the current is turned off via the logic inputs.When both I1 and I0 are high, all four transistors in the output H-bridge are turned off, which means that inductive current recirculates through two opposite free-wheeling diodes (see figure 3, arrow 3). this method of turning off the current results in a faster current decay than if only one transistor was turned off and will therefore improve speed performance in half-stepping mode. NJM3770A ■ ABSOLUTE MAXIMUM RATINGS Parameter Pin no. [DIP package] Symbol Min Max Unit 0 7 V Voltage Logic supply 6 VCC Motor supply 3, 14 VMM 0 45 V Logic inputs 7,8,9 VI -0.3 6 V Comparator input 10 VC -0.3 VCC V Reference input 11 VR -0.3 15 1, 15 IM -1800 +1800 mA Current Motor output current Logic inputs 7,8,9 II -10 - mA Analog inputs 10,11 IA -10 - mA Operating junction temperature Tj -40 +150 °C Storage temperature Ts -55 +150 °C Temperature ■ RECOMMENDED OPERATING CONDITIONS Parameter Symbol Logic supply voltage Motor supply voltage Motor output current Junction temperature Rise time logic inputs Fall time logic inputs Min VCC VMM IM TJ tr tf 4.75 10 -1500 -20 - VMM V CC 6 [18] I IH I IL Schmitt Trigger 1 8 I 7 15 MA I0 9 1 MB VR 11 ≥1 ≥1 ≥1 & & & & IM I OL t on VI VA V IH V V IL t Output Stage VM + – td MA Monostable t off = 0.69 • R T• C T + – 4, 5, 12, 13 VE V MM V R GND t off 1/2 ≥1 + – VCC V V mA °C µs µs Normalized 1 IA 5.25 40 +1500 +125 2 2 | V MA – V MB | VMM Phase 1 Unit 14 3 Time Delay Max 5 - I MM I CC II Typ V CH Current Sensor 10 IC C 2 16 T E NJM3770A V CM 1k IA V RC VE VC 820 pF CC 820 pF 56 k RT CT 0.5 R Pin no. refers to DIP-package CL t S 1 f= s t +t on off Figure 5. Definition of symbols D= ton t on + t off Figure 6. Definition of terms NJM3770A ■ ELECTRICAL CHARACTERISTICS Electrical characteristics over recommended operating conditions. CT = 820 pF, RT = 56 kohm Parameter Symbol General Supply current ICC Total power dissipation PD Turn-off delay Thermal shutdown junction temperature td Logic Inputs Logic HIGH input voltage Logic LOW input voltage Logic HIGH input current Logic LOW input current VIH VIL IIH IIL Analog Inputs Comparator threshold voltage Comparator threshold voltage Comparator threshold voltage Input current VCH VCM VCL IC Motor Outputs Lower transistor saturation voltage VMM = 20 to 40 V, I0 = I1 = HIGH. VMM = 20 to 40 V, I0 = I1 = LOW, fs = 23 kHz fs = 28 kHz, IM = 1.0A, VMM = 36 V Note 2, 4. fs = 24 kHz, IM = 1.0A, VMM = 12 V Note 2, 4. fs = 28 kHz, IM = 1.3A, VMM = 36 V Note 3, 4. fs = 28 kHz, IM = 1.5A, VMM = 36 V Note 3, 4. Ta = +25°C, dVC/dt ≥ 50 mV/µs. VI = 2.4 V VI = 0.4 V VR = 5.0 V, I0 = I1 = LOW VR = 5.0 V, I0 = HIGH, I1 = LOW VR = 5.0 V, I0 = LOW, I1 = HIGH IM = 1.0A IM = 1.3A IM = 1.0A IM = 1.3A IM = 1.0A IM = 1.3A I0 = I1 = HIGH, Ta = +25°C Lower diode forward voltage drop Upper transistor saturation voltage Output leakage current Monostable Cut off time Conditions toff VMM = 10 V, ton ≥ 5 µs Min Typ Max Unit - 30 48 40 65 mA mA - 1.9 2.3 W - 1.7 2.1 W - 2.7 3.2 W - 3.5 - W - 170 2.5 - µs °C 2.0 -0.4 - 0.8 20 - V V µA mA 400 240 70 -20 415 250 80 - 430 265 90 - mV mV mV µA - 0.5 0.8 1.3 1.5 1.1 1.3 - 0.8 1.3 1.6 1.8 1.3 1.6 100 V V V V V V µA 27 31 35 µs Min Typ Max Unit - 11 40 9 35 11 40 - °C/W °C/W °C/W °C/W °C/W °C/W ■ THERMAL CHARACTERISTICS Parameter Symbol Thermal resistance RthJ-GND RthJ-A RthJ-GND RthJ-A RthJ-GND RthJ-A Conditions DIP package. DIP package. Note 2. PLCC package. PLCC package. Note 2. EMP package. EMP package. 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=+25°C 3. DIP package with external heatsink (Staver V7) and minimal copper area. Typical RthJ-A = 27.5°C/W. Ta = +25°C 4. Not covered by final test program NJM3770A ■ 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 µF ceramic capacitor, located near the package across the power line VMM and ground. Also make sure that the VRef 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, VCC and VMM, 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 being generated by the motor. 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 RT, CT components than those recommended in figure 3, to obtain a switching frequency above the audible range. Switching frequencies above 40 kHz are not recommended because the current regulation can be affected. VCC (+5V) V MM 11 Phase 8 A I 1A I 0A Phase 7 I1 9 I0 T V R 6 V CC V MM C 56 k E 1k 8 7 9 V MM V Phase R I1 3,14 V CC GND 2 56 k 6 V MM NJM3770A I0 T 820pF 0.5 820pF 11 I 1A I 0A 15 A 16 VCC (+5V) A M 10 4, 5 12, 13 820pF Phase 1 M B NJM3770A GND 2 STEPPER MOTOR 3,14 4, 5 12, 13 C M B 1 M 15 A E 10 16 1k 820pF 0.5 Diodes are UF 4001 or BYV27 t ≤ 100 ns Figure 7. Typical stepper motor driver application with NJM3770A NJM3770A Analog control As the current levels can be continuously controlled by modulating the VR input, limited microstepping can be achieved. Sensor resistor The RS resistor should be of a noninductive type power resistor. A 0.5 ohm resistor, tolerance ≤ 1%, is a good choice for 800 mA max motor current at VR = 5V. The peak motor current, im , can be calculated by using the formula: im = (VR • 0.080) / RS [A], at 100% level External recirculation diodes Recirculation diodes must be connected across each motor terminal and the supply voltage, VMM. The anodes shall be connected to the motor terminals and the cathodes to the VMM voltage. Ultra-fast recovery diodes should be used for maximum performance and reliability. I 0A I 1A Ph A Thermal resistance [°C/W] Ph B 90 16-pin DIP 80 I 0B I 1B I MA 70 100% 60% 60 –20% –60% –100% 50 20-pin EMP I MB 100% 60% 20% 40 30 5 10 15 20 25 30 –60% –100% 35 PCB copper foil area [cm 2 ] PLCC package DIP package Full step position 28-pin PLCC Half step position Stand by mode at 20 % Figure 8. Copper foil used as a heatsink Half step mode at 100 % Figure 9. Principal operating sequence. Full step mode at 60 % NJM3770A 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 NJM3770A can be reduced by soldering the ground pins to a suitable copper ground plane on the printed circuit board (see figure 8) or by applying an external heatsink type V7 or V8, see figure 10. The diagram in figure 15 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 approx 600 mA, some form of heatsinking is recommended to assure optimal reliability. The diagrams in figures 14 and 15 can be used to determine the required heatsinking of the circuit. In some systems, forced-air cooling may be available to reduce the temperature rise of the circuit. 33,5 mm 11,6 mm 38,5 mm 18,5 m m mm 38.0 Figure 10. Heatsinks, Staver, type V7 and V8 by Columbia-Staver UK mm 38.0 NJM3770A ■ TYPICAL CHARACTERISTICS VSat (V) VF (V) VSat (V) 1.8 1.8 1.8 1.6 1.6 1.4 1.4 1.2 1.2 1.6 Tj = 25 °C 1.4 1.2 Tj = 125°C 1.0 1.0 .8 .8 .6 .6 .4 .4 .4 .2 .2 .2 Tj = 25°C 1.0 .8 Tj = 125°C .6 0 0 .40 .80 1.2 1.6 0 0 .40 .80 Figure 11. Typical source saturation vs. output current PD (W) 1.2 1.6 I M (A) I M (A) Figure 12. Typical lower diode voltage drop vs. recirculating current 0 Tj = 125°C Tj = 25°C 0 .40 .80 1.2 1.6 I M (A) Figure 13. Typical sink saturation vs. output current PD (W) VMM = 36 V 3.0 4.0 2.0 B er he V8 at (3 sin 7. k( 5° C/ W ) 40 °C /W ) ) W C/ 1.0 av 5° 2.0 VMM = 12 V PC 7. (2 1.5 St V7 er av St 3.0 ith ith W 2.5 W 1.0 .5 0 0 .50 1.0 1.5 I M (A) Figure 14. Typical power dissipation vs. motor current 0 50 100 150 TAmb (°C) Figure 15. 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.