NJM3771 DUAL STEPPER MOTOR DRIVER ■ GENERAL DESCRIPTION The NJM3771 is a stepper motor driver, which circuit is especially developed for use in microstepping applications in conjunction with the matching dual DAC (Digital-to-Analog Converter) NJU39610. The NJM3771 contains a clock oscillator, which is common for both driver channels; a set of comparators and flip-flops imple menting the switching control; and two H-bridges with internal recirculation diodes. Voltage supply requirements are +5 V for logic and +10 to +45 V for the motor. Maximum output current is 650 mA per channel. ■ PACKAGE OUTLINE NJM3771D2 ■ FEATURES NJM3771E3 NJM3771FM2 • Dual chopper driver • 650 mA output current per channel • Selectable slow/fast current decay for improved highspeed microstepping • Specially matched to Dual DAC NJU39610 • Packages DIP22 / EMP24(Batwing) / PLCC28 ■ BLOCK DIAGRAM Phase 1 CD 1 V R1 E1 C1 NJM 3771 – V VCC CC + R S Q M A1 + M B1 Logic – V MM1 + V MM2 – M B2 – M A2 Logic + RC + – Phase 2 Figure 1. Block diagram CD2 V R2 C2 S R GND Q E2 NJM3771 V MM2 MA1 4 19 MA2 GND 5 18 GND 26 CD 2 20 27 Phase 2 V MM1 3 1 GND E2 28 GND 21 2 GND 23 MB2 VR1 10 15 VR2 C1 11 14 C2 VCC 12 13 RC GND Phase 1 7 16 Phase 2 CD1 8 15 CD2 VR1 9 14 VR2 C 1 10 13 C2 VCC 11 12 RC 23 RC M B1 8 GND 9 NJM 3771FM2 22 VCC 21 C 1 E1 10 20 V R1 VMM1 11 19 CD1 GND 17 16 CD2 17 Phase1 18 CD1 9 NJM 3771D2 GND 16 17 Phase2 GND 6 24 C 2 M B2 7 GND 15 18 GND 25 V R2 E2 6 GND 14 Phase1 8 19 GND V MM2 5 MA1 12 NJM 3771E3 20 VMM2 GND 13 21 MA2 MA1 4 GND 7 E1 2 22 E2 E1 3 GND 6 MB2 24 NC MB1 2 VMM1 5 22 3 GND NC 1 MB1 1 4 MA2 ■ PIN CONFIGURATIONS Figure 2. Pin configurations ■ PIN DESCRIPTION Refer to Figure 2 EMP DIP PLCC Symbol 1 2 3 4 5,6, 17,18 8 10 11 12 1-3,9, 13-17,28 MB1 E1 VMM1 MA1 GND 8 7 18 Phase1 9 8 19 CD1 10 9 20 VR1 11 10 21 C1 12 11 22 VCC 13 12 23 RC 14 13 24 C2 15 14 25 VR2 16 15 26 CD2 17 16 27 Phase2 20 21 22 23 19 20 21 22 4 5 6 7 MA2 VMM2 E2 MB2 2 3 4 5 6,7, 18,19 Description Motor output B, channel 1. Motor current flows from MA1 to MB1 when Phase1 is HIGH. Common emitter, channel 1. This pin connects to a sensing resistor to ground. Motor supply voltage, channel 1, 10 to 40 V. VMM1 and VMM2 should be connected together. Motor output A, channel 1. Motor current flows from MA1 to MB1 when Phase1 is HIGH. Ground and negative supply. Note: these pins are used thermally for heat-sinking. Make sure that all ground pins are soldered onto a suitably large copper ground plane for efficient heat sinking. Controls the direction of motor current at outputs MA1 and MB1. Motor current flows from MA1 to MB1 when Phase1 is HIGH. Current decay control, channel 1. A logic HIGH on this input results in slow current decay, a LOW results in fast current decay, see “Functional Description.” Reference voltage, channel 1. Controls the threshold voltage for the comparator and hence the output current. Input resistance is typically 2.5 kohms, ±20%. Comparator input channel 1. This input senses the instantaneous voltage across the sensing resistor, filtered by an RC network. The threshold voltage for the comparator is (0.450 / 2.5) • VR1, i.e. 450 mV at VR1 = 2.5 V. Logic voltage supply, nominally +5 V. Clock oscillator RC pin. Connect a 15 kohm resistor to VCC and a 3300 pF capacitor to ground to obtain the nominal switching frequency of 26.5 kHz. Comparator input channel 2. This input senses the instantaneous voltage across the sensing resistor, filtered by an RC network. The threshold voltage for the comparator is (0.450 / 2.5) • VR1, i.e. 450 mV at VR1 = 2.5 V. Reference voltage, channel 2. Controls the threshold voltage for the comparator and hence the output current. Input resistance is typically 2.5 kohms, ±20%. Current decay control, channel 2. A logic HIGH on this input results in slow current decay, a LOW results in fast current decay, see “Functional Description.” Controls the direction of motor current at outputs MA2 and MB2. Motor current flows from MA2 to MB2 when Phase2 is HIGH. Motor output A, channel 2. Motor current flows from MA2 to MB2 when Phase2 is HIGH. Motor supply voltage, channel 2, 10 to 40 V. VMM1 and VMM2 should be connected together. Common emitter, channel 2. This pin connects to a sensing resistor to ground. Motor output B, channel 2. Motor current flows from MA2 to MB2 when Phase2 is HIGH. NJM3771 ■ FUNCTIONAL DESCRIPTION Each channel of the NJM3771 consists of the following sections: an H-bridge output stage, capable of driving up to 650 mA continuous motor current (or 500 mA, both channels driven), a logic section that controls the output transistors, an S-R flip-flop, and two comparators. The oscillator is common to both channels. Constant current control is achieved by switching the current to the windings. This is done by sensing the (peak) voltage across a current-sensing resistor, RS, effectively connected in series with the motor winding, and feeding that voltage back to a comparator. When the motor current reaches a threshold level, determined by the voltage at the reference input, VR, the comparator resets the flip-flop, which turns off the output transistors. The current decreases until the clock oscillator triggers the flip-flop, which turns on the output transistors again, and the cycle is repeated. The current-decay rate during the turn-off portion of the switching cycle, can be selected fast or slow by the CD input. In slow current-decay mode, only one of the lower transistors in the H-bridge (those closest to the negative supply) is switched on and off, while one of the upper transistors is held constantly on. During turn-off, the current recirculates through the upper transistor (which one depends on current direction) and the corresponding freewheeling diode connected to VMM, see figure 3. In fast current decay mode, both the upper and lower transistors are switched. During the off-time, the freewheeling current is opposed by the supply voltage, causing a rapid discharge of energy in the winding. Fast current decay may be required in half- and microstepping applications when rapid changes of motor current are necessary. Slow current decay, however, gives less current ripple, and should always be selected, if possible, to minimize core losses and switching noise. 2 1 3 Rs Motor Current 1 2 FAST Current Decay 3 Time SLOW Current Decay Figure 3. Output stage with current paths during turn -on, turn-off and phase shift NJM3771 ■ ABSOLUTE MAXIMUM RATINGS Parameter Pin no. (DIP) Symbol Min Max Unit Voltage Logic supply Motor supply Logic inputs Comparator inputs Reference inputs 11 3, 20 7, 8, 15, 16 10, 13 9, 14 VCC VMM VI VC VR 0 0 -0.3 -0.3 -0.3 7 45 6 VCC 7.5 V V V V V Current Motor output current Logic inputs Analog inputs Oscillator charging current 1, 4, 19, 22 7, 8, 15, 16 10, 13 12 IM II IA IRC -700 -10 -10 - +700 5 mA mA mA mA TJ TS -40 -55 +150 +150 °C °C Symbol Min Typ Max Unit VCC VMM IM TJ tr tf RT 4.75 10 -650 -20 2 5 15 5.25 40 650 +125 2 2 20 V V mA °C µs µs kohm Temperature Operating junction temperature Storage temperature** ** Circuit only. The packaging can handle max 60°C ■ RECOMMENDED OPERATING CONDITIONS Parameter Logic supply voltage Motor supply voltage Motor output current *** Junction temperature **** Rise time logic inputs Fall time logic inputs Oscillator timing resistor *** In microstepping mode, “sine/cosine” drive where I1 = 650 • cos(q) and I2 = 650 • sin(q) mA, otherwise 500 mA/channel both channels fully on. ****See operating temperature chapter. Phase 1 7 CD 1 V R1 C1 E1 8 10 2 9 NJM 3771 VCC I CC | V MA – V MB | – V CC 11 + R S Q 4 + Logic – M A1 1 M B1 3 V MM1 t off t on 50 % 15 kΩ + RT – – Logic + I RC RC 12 + – S R 20 V MM2 22 M B2 19 M A2 I MM IM t I OL VE Q V 3 300 pF CH VCC CT 16 Phase 2 II I IH 15 14 13 CD2 V R2 I IL C2 IA VIL 5, 6, 17, 18 21 E2 GND IC IA VI VIH td 1 kΩ VA VCH VR VC RC CC Figure 4. Definitions of symbols VE VM VMA 820 pF RS t V MM 1 fs = t + t on off ton D= ton + t off Figure 5. Definition of terms NJM3771 ■ ELECTRICAL CHARACTERISTICS Electrical characteristics over recommended operating conditions, unless otherwise noted. -20°C < TJ < +125°C Parameter General Supply current Total power dissipation Turn-off delay Symbol ICC PD td Logic Inputs Logic HIGH input voltage Logic LOW input voltage Logic HIGH input current Logic LOW input current VIH VIL IIH IIL Reference Inputs Input resistance Input current Turn-off voltage RR IR VTO Comparator Inputs Threshold voltage | VCH1 - VCH2 | mismatch Input current VCH VCH,diff IC Motor Outputs Lower transistor saturation voltage Lower transistor leakage current Lower diode forward voltage drop Upper transistor saturation voltage Upper transistor leakage current Upper diode forward voltage drop Chopper Oscillator Chopping frequency Conditions VMM = 40 V, IM1= 450 mA, IM2= 0 mA. Notes 2, 3. VMM = 40 V, IM1 = IM2 = 318 mA. Notes 2, 3. Ta = +25°C, dVC/dt ≥ 50 mV/µs. Note 3. VI = 2.4 V VI = 0.4 V Ta = +25°C Ta = +25°C, VR = 2.5 V. RC = 1 kohms, VR = 2.5 V RC = 1 kohms IM = 500 mA VMM = 41 V, VE = VR = 0 V, VC = VCC IM = 500 mA IM = 500 mA VMM = 41 V, VE = VR = 0 V, VC = VCC IM = 500 mA fs Min CT = 3300 pF, RT = 15 kohms Typ Max Unit 38 1.4 50 1.6 mA W 1.6 1.8 W - 1.0 1.5 µs 2.0 -0.4 - 0.6 20 - V V µA mA 20 5 0.5 29 1.0 38 kohm mA mV 430 -10 450 1 - 470 1 mV mV µA - 1.00 1.10 1.20 1.00 1.20 300 1.25 1.35 300 1.25 V µA V V µA V 25.0 26.5 28.0 kHz ■ THERMAL CHARACTERISTICS Parameter Thermal resistance Symbol Conditions Min Typ RthJ-GND RthJ-A RthJ-GND RthJ-A RthJ-GND DIP package. DIP package. Note 2. PLCC package. PLCC package. Note 2. EMP package. - 11 40 9 35 13 - °C/W °C/W °C/W °C/W °C/W RthJ-A EMP package. Note 2. - 42 - °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. 3. Not covered by final test program. 4. Switching duty cycle D = 30%, fS = 26.5 kHz Max Unit NJM3771 ■ APPLICATIONS INFORMATION Current control The output current to the motor winding is mainly determined by the voltage at the reference input and the value of the sensing resistor, RS. Chopping frequency, winding inductance, and supply voltage will affect the current level, but to much less extent. Fast current decay setting will produce somewhat lower (average) current than slow current decay. The peak current through the sensing resistor (and motor winding) can be expressed as: IM,peak = 0.18 • (VR / RS) [A] i.e., with a recommended value of 1 ohm for the sensing resistor, RS, a 2.5 V reference voltage will produce an output current of approximately 450 mA. To improve noise immunity on the VR input, the control range may be increased to 5 volts if RS is correspondingly changed to 2 ohms. V MM V CC (+5 V) + 0.1 µF 0.1 µF 11 V 7 8 9 16 15 14 3 V CC 20 V MM1 MM2 Phase 1 CD1 V R1 MA1 4 MB1 1 NJM 3771 19 MA2 Phase 2 CD 2 V R2 RC GND 12 +5 V 15 kΩ 22 MB2 C1 5, 6, 17, 18 E1 3 300 pF C2 2 10 1 kΩ 820 pF 820 pF 1.0 Ω STEPPER MOTOR E2 21 13 1 kΩ GND (V CC ) 10 µF Pin numbers refer to DIP package. 1.0 Ω RS RS GND (V MM ) Figure 6. Typical stepper motor application with NJM3771 V MM V CC (+5 V) + 0.1 µF 0.1 µF 11 5 14 V V DD D0 Sign1 CD1 7 To P +2.5V 15 16 6 17 22 1 D7 NJU 39610 A0 A1 WR CS RESET V Ref DA1 Sign2 CD2 V SS DA2 3 7 4 8 2 9 20 16 19 15 21 14 MM2 CD1 V R1 MA1 4 MB1 1 NJM 3771 MA2 Phase 2 CD 2 V R2 RC GND +5 V 15 kΩ 3 300 pF GND (V CC ) 20 V MM1 Phase 1 12 18 3 V CC 5, 6, 17, 18 MB2 C1 E1 C2 2 10 820 pF 820 pF Figure 7. Microstepping system with NJU39610 and NJM3771 22 STEPPER MOTOR E2 1 kΩ RS 19 21 13 1 kΩ 1.0 Ω 10 µF 1.0 Ω Pin numbers refer to DIP package. RS GND (V MM ) NJM3771 External components The voltage across the sensing resistor is fed back to the comparator via a low-pass filter section, to prevent erroneous switching due to switching transients. The recommended filter component values, 1 kohm and 820 pF, are suitable for a wide range of motors and operational conditions. Since the low-pass filtering action introduces a small delay of the signal to the comparator, peak voltage across the sensing resistor, and hence the peak motor current, will reach a slightly higher level than the threshold, VC, set by the reference voltage (VC = 450 mV @VR = 2.5 V). The time constant of the low-pass filter may therefore be reduced to minimize the delay and optimize low-current performance, especially if a low (12 V) supply voltage is used. Increasing the time constant may result in unstable switching. The frequency of the clock oscillator is set by the R-C combination at pin RC. The recommended values give a nominal frequency of 26.5 kHz. A lower frequency will result in higher current ripple and may cause audible noise from the motor, while increasing the frequency results in higher switching losses and possibly increased iron losses in the motor. The sensing resistor, RS, should be selected for maximum motor current. The relationship between peak motor current, reference voltage and the value of RS is described under “Current control” above. Be sure not to exceed the maximum output current which is 650 mA per channel (or 500 mA per channel, both channels fully on, see “Recommended Operating Conditions”). Motor selection The NJM3771 is designed for bipolar motors, i.e., motors that have only one winding per phase. A unipolar motor, having windings with a center tap, can also be used, see figure 8. The chopping principle in the NJM3771 is based on a constant frequency and a varying duty cycle. This scheme imposes certain restrictions on motor selection. Unstable chopping can occur if the chopping duty cycle exceeds approximately 50%. To avoid this, it is necessary to choose a motor with a low winding resistance. Low winding resistance means less inductance and will therefore enable higher stepping rates, however it also means less torque capability. A compromise has to be made. Choose a motor with the lowest possible winding resistance that still gives the required torque and use as high supply voltage as possible without exceeding the maximum recommended 40 V. Check that the chopping duty cycle does not exceed 50% at maximum current. Since the NJM3771 produces a regulated, constant output current it is not necessary to use a motor that is rated at the same voltage as the actual supply voltage. Only rated current needs to be considered. Typical motors to be used together with the NJM3771 have voltage ratings of 5 to 12 V, while the supply voltage usually ranges from 24 to 40 V. Best for high speed NJM3771 Figure 8. Connection of unipolar motors Best for high torque NJM3771 NJM3771 General Phase inputs A logic HIGH on a Phase input gives positive current flowing out from MA into MB. A logic LOW gives a current in the opposite direction. Slow/fast current decay A logic HIGH on the CD input gives slow current decay, a logic LOW gives fast current decay. Heat sinking Soldering the four center pins onto a free PCB copper area of 20 cm2 (approx. 1.8" x 1.8", copper foil thickness = 35 µm) permits the circuit to operate with a maximum of 320 mA output current, both channels driving, at ambient temperatures up to +70°C. Consult figures 9 and 14 in order to determine the necessary copper area for heat sinking if higher currents are required. Thermal shutdown The circuit is equipped with a thermal shutdown function that reduces the output current at chip temperatures above +160°C. Thermal resistance [°C/W] 80 70 22-pin DIP 60 50 24-pin EMP 40 30 20 5 10 15 20 25 30 35 PCB copper foil area [cm 2 ] PLCC package DIP package Figure 9. Thermal Resistance vs. PC Board copper area and suggested layout 28-pin PLCC NJM3771 ■ TYPICAL CHARACTERISTICS Vd (V) VCE Sat (V) Vd (V) 1.2 1.0 Tj = 25°C Tj = 25°C 1.0 .8 1.0 Tj = 125°C .6 .8 .4 .6 .2 .4 0 0 .10 .20 .30 .40 .50 .60 .2 Tj = 125°C .6 Tj = 125°C .4 .2 0 .10 IM (A) .20 .30 .40 .50 0 .60 0 .10 .20 I M (A) Figure 10. Typical upper diode voltage drop vs. recirculating current .30 .40 .50 .60 I M (A) Figure 11. Typical source saturation voltage vs. output current Figure 12. Typical lower diode voltage drop vs. recirculating current PD (W) VCE Sat (V) 1.0 .8 Tj = 25°C Tj = 25°C 3.0 VMM = 36V .8 Tj = 125°C .6 2.0 VMM = 14V .4 1.0 .2 0 .10 .20 .30 .40 .50 .60 I M (A) Figure 13 Typical sink saturation voltage vs. output current 00 .10 Max allow power is .20 .30 .40 .50 .60 I M (A) Figure 14. Power dissipation vs. motor current, both channels driven, Ta = 25°C 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.