NJM3774 DUAL STEPPER MOTOR DRIVER ■ GENERAL DESCRIPTION The NJM3774 is a switch-mode (chopper), constantcurrent driver with two channels: one for each winding of a two-phase stepper motor. The NJM3774 is equipped with a TTL level compatible Disable input to simplify half-stepping operation. The circuit is well suited for microstepping applications together with the matching dual DAC NJU39610. In full/half stepping applications, the NJM3517 can be used as a phase generator (translator) to derive the necessary signals for the NJM3774. The NJM3774 contains a clock oscillator, which is common for both driver channels, a set of comparators and flip-flops implementing the switching control, and two output H-bridges. Voltage supply requirements are +5 V for logic and +10 to +45 V for the motor. Maximum output current is 1000mA per channel. ■ PACKAGE OUTLINE NJM3774D2 NJM3774FM2 ■ FEATURES • Dual chopper driver • 1000 mA continuous output current per channel • Specially matched to the Dual DAC NJU39610 • Packages DIP22 / PLCC28 ■ BLOCK DIAGRAM Phase 1 Dis1 VR1 E1 C1 NJM3774 VCC – V CC + R S Q M A1 M B1 Logic V MM1 + V MM2 – M B2 Logic M A2 RC + – Phase 2 Figure 1. Block diagram Dis 2 V R2 C2 S R GND Q E2 NJM3774 GND Phase 2 26 GND 1 Dis 2 GND 2 27 GND 3 28 MA2 4 ■ PIN CONFIGURATIONS RC 1 22 VCC C2 2 21 C 1 V R2 3 VMM2 5 25 VR2 E2 6 24 C2 M B2 7 23 RC NJM3774FM2 22 VCC GND 9 21 C1 E1 10 20 VR1 VMM1 11 19 Phase1 M B1 8 Dis 1 18 GND 17 GND 16 GND 15 GND 14 M A1 12 19 Phase 1 Phase 2 4 GND 5 GND 6 Dis2 7 MA2 8 VMM2 9 GND 13 20 VR1 E 2 10 MB2 11 18 GND NJM 3774D2 17 GND 16 Dis1 15 MA1 14 VMM1 13 E 1 12 MB1 Figure 2. Pin configurations ■ PIN DESCRIPTION PLCC DIP 1-3, 9, 13-17 28 4 5 6 7 8 10 11 5, 6 GND 17, 18 Symbol 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. Description 8 9 10 11 12 13 14 MA2 VMM2 E2 MB2 MB1 E1 VMM1 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 RS to ground. Motor output B, channel 2. Motor current flows from MA2 to MB2 when Phase2 is HIGH. 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 RS to ground. Motor supply voltage, channel 1, +10 to +40 V. VMM1 and VMM2 should be connected together. 12 18 15 16 MA1 Dis1 19 19 Phase1 20 20 VR1 21 21 C1 22 23 22 1 VCC RC 24 2 C2 25 3 VR2 26 4 Phase2 27 7 Dis2 Motor output A, channel 1. Motor current flows from MA1 to MB1 when Phase1 is HIGH. Disable input (TTL level compatible) for channel 1. When HIGH, all four output transistors are turned off, which results in a rapidly decreasing output current to zero. Controls the direction of motor current at outputs MA1 and MB1. Motor current flows from MA1 to MB1 when Phase1 is HIGH. Ref. voltage, channel 1. Controls the threshold voltage for the comparator and hence the output current. 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 VCH1= 0.18 • VR1 [V], 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 VCH2= 0.18 • VR2 [V], i.e. 450 mV at VR2 = 2.5 V. Ref. voltage, channel 2. Controls the threshold voltage for the comparator and hence the output current. Controls the direction of motor current at outputs MA2 and MB2. Motor current flows from MA2 to MB2 when Phase2 is HIGH. Disable input (TTL level compatible) for channel 2. When HIGH, all four output transistors are turned off, which results in a rapidly decreasing output current to zero. NJM3774 ■ FUNCTIONAL DESCRIPTION Each channel of the NJM3774 consists of the following sections: an output H-bridge with four transistors, capable of driving up to 1000mA continuous current to the motor winding; a logic section that controls the output transistors; an S-R flip-flop; and a comparator. The clock-oscillator is common to both channels. Constant current control is achieved by switching the output current to the windings. This is done by sensing the peak current through the winding via a resistor, RS, effectively connected in series with the motor winding during the turn-on period. As the current increases, a voltage develops across the resistor, and is fed back to the comparator. At the predetermined level defined by the voltage at the reference input VR, the comparator resets the flip-flop, turning off the output transistors. The current decreases until the clock oscillator triggers the flip-flop, turning on the output transistors, and the cycle is repeated. The current paths during turn-on, turn-off and phase shift are shown in figure 3. Note that the upper recirculation diodes are connected to the circuit externally. External recirculation diodes V MM 1 2 3 R S Motor Current 1 2 3 Fast Current Decay Slow Current Decay Figure 3. Output stage with current paths during turn-on, turn-off and phase shift. Time NJM3774 ■ ABSOLUTE MAXIMUM RATINGS Parameter Pin no. [DIP-package] Symbol Min Max Unit Voltage Logic supply Motor supply Logic inputs Comparator inputs Reference inputs 22 9, 14 4, 7, 16, 19 2, 21 3, 20 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 8, 11, 12, 15 4, 7, 16, 19 2, 3, 20, 21 IM II IA -1200 -10 -10 +1200 - mA mA mA Temperature Operating Junction temperature Storage temperature Tj Tstg -40 -55 +150 +150 °C °C Power Dissipation (Package Data) Power dissipation at TGND = +25°C, DIP and PLCC package Power dissipation at TGND = +125°C, DIP package Power dissipation at TGND = +125°C, PLCC package PD PD PD - 5 2.2 2.6 W W W ■ RECOMMENDED OPERATING CONDITIONS Parameter Symbol Logic supply voltage Motor supply voltage Motor output current Operating Junction temperature Rise and fall time, logic inputs Oscillator timing resistor VCC VMM IM TJ tr, tf RT Phase 1 Dis 1 VR1 19 16 20 C1 E1 21 13 Min Typ Max Unit 4.75 10 -1000 - 20 2 5 15 5.25 40 +1000 +125 2 20 V V mA °C µs kΩ NJM3774 VCC I CC – V 22 CC + R S Q Logic 15 M A1 12 M B1 14 V MM1 9 V MM2 11 M B2 8 M A2 | V MA – V MB | t on 15 kW + RT – Logic I RC RC 1 + – S R IM t off 50 % I MM I OL t Q VE td 3 300 pF V VCC CT 4 Phase 2 II I IH I IL IR IA VA V IL 2 5, 6, 17, 18 C2 GND CH 10 E2 IC IA VM 1 kW V V V V 3 Dis 2 V R2 VCH VI IH 7 R RC C 820 pF CC Figure 4. Definition of symbols VE MA t V MM 1 RS fs = t + t on off ton D= ton + t off Figure 5. Definition of terms NJM3774 ■ ELECTRICAL CHARACTERISTICS Electrical characteristics over recommended operating conditions unless otherwise noted, - 20°C ≤ TJ ≤ +125°C. Parameter Symbol General Supply current Total power dissipation ICC PD Total power dissipation PD Thermal shutdown junction temperature Turn-off delay td Logic Inputs Logic HIGH input voltage Logic LOW input voltage Logic HIGH input current Logic LOW input current Comparator Inputs Threshold voltage | VCH1 - VCH2 | mismatch Input current Reference Inputs Input resistance Input current VIH VIL IIH IIL VCH VCH,diff IC RR IR Motor Outputs Lower transistor saturation voltage Lower transistor leakage current Lower diode forward voltage drop Upper transistor saturation voltage Upper transistor leakage current Chopper Oscillator Chopping frequency fs Conditions Min Typ Max Unit - 60 2.6 75 2.9 mA W - 2.6 2.9 W - 160 1.4 2.0 °C µs 2.0 -0.4 - 0.8 20 - V V µA mA 430 -10 450 1 - 470 1 mV mV µA TA = +25°C VR = 2.5 V - 5 0.5 1.0 kohm mA IM = 750 mA VMM = 41 V, VE = VR = 0 V, VC = VCC IM = 750 mA IM = 750 mA. VMM = 41 V, VE = VR = 0 V, VC = VCC - 0.6 1.2 1.1 - 0.9 700 1.5 1.4 700 V µA V V µA 25.0 26.5 28.0 kHz Min Typ Max - 11 40 9 35 Note 4. VMM = 12 V, IM1 = IM2 = 750 mA. Notes 2, 3, 4. VMM = 12 V, IM1 = 1000 mA, IM2 = 0 mA. Notes 2, 3, 4. TA = +25°C, dVC/dt ≥ 50 mV/µs. IM = 100 mA. Note 3. VI = 2.4 V VI = 0.4 V RC = 1 kohm, VR = 2.50 V RC = 1 kohm CT = 3300 pF, RT = 15 kohm ■ THERMAL CHARACTERISTICS Parameter Symbol Thermal resistance RthJ-GND RthJ-A RthJ-GND RthJ-A Conditions DIP package. DIP package. Note 2. PLCC package. PLCC package. Note 2. 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. Not covered by final test program. 4. Switching duty cycle D = 30%, fs = 26.5 kHz. - Unit °C/W °C/W °C/W °C/W NJM3774 ■ APPLICATIONS INFORMATION Current control The output current to the motor is de-termined by the voltage at the reference input and value of sensing resistor, RS. Chopping frequency, winding induc-tance and supply voltage also affect the current, but to much less extent. The output current can be switched off com-pletely by a HIGH input level at the Dis-able input (Dis1 and Dis2 for respective channels). When Disable goes HIGH, all four transistors in the output stage are switched off, and the output current rapidly drops to zero (“fast current decay” – see figure 3). The peak motor current through the sensing resistor and the motor winding can be expressed as: IM,peak = 0.18 • ( VR / RS ) [A] A 2.5 V reference voltage and a 0.47 ohm sensing resistor will produce an out-put current level of approximately 960 mA. To improve noise immunity at the VR input, the voltage control range can be increased to 5 V if RS is correspondingly changed (for example to 1ohm for 900 mA max output current). External components For the device to function properly, four external free-wheeling diodes must be connected, as in figure 6. The diodes should be of fast type with a reverse recovery time of less than 100 ns. Com-monly used types are UF4001 or BYV27. A low pass filter in series with the com-parator input prevents erroneous switch-ing 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 in-troduces 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 what is defined by the comparator threshold, VCH , set by the reference input VR (VCH = 450 mV at VR= 2.5 V). The time constant of the low-pass fil-ter may therefore be reduced to minimize the delay and optimize low-current performance. Increasing the time constant may result in unstable switching. The time constant should be adjusted by changing the CC value. V MM +5 V + 0.1 µF 10 µF D1 22 V 19 11 V CC 5 V MM1 Phase 1 18 MM2 MA1 Dis1 20 MB1 V R1 NJM3774 26 MA2 Phase 2 27 D2 12 8 4 Dis 2 25 V R2 RC GND 23 +5 V 15 kΩ 3300 pF 1, 2, 3, 9, 13, 14, 15, 16, 17, 28. M C1 21 E1 10 C2 STEPPER MOTOR 6 1 kΩ D3 820 pF D4 V MM 820 pF RS RS 0.68 Ω GND (VCC ) 7 E2 24 1 kΩ B2 0.68 Ω D1 - D4 are UF 4001 or BYV 27, trr ≤ 100 ns. Pin numbers refer to PLCC package. Figure 6. Typical stepper motor driver application with NJM3774. NJM3774 The frequency of the clock oscillator is set by the RT-CT timing components at the RC pin. The recommended values result in a clock frequency (= switching frequency) of 26.5 kHz. A lower frequency will result in higher current ripple, but may improve low-current level linearity. A higher clock frequency reduces current ripple, but increases the switching losses in the IC and possibly increased iron losses in the motor. If the clock frequency needs to be changed, the CT capacitor value should be adjusted. The recommended RT resistor value is 15 kohm. 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 1200mA peak when only one channel is activated. Or recommended output current, which is 1000mA peak, when both channels is activated. Motor selection The NJM3774 is designed for two-phase bipolar stepper motors, i.e. motors that have only one winding per phase. The chopping principle of the NJM3774 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%. See figure 5 for definitions. To avoid this, it is necessary to choose a motor with a low winding resistance and inductance, i.e. windings with a few turns. It is not possible to use a motor that is rated for the same voltage as the actual supply voltage. Only rated current needs to be considered. Typical motors to be used together with the NJM3774 have a voltage rating of 1 to 6 V, while the supply voltage usually ranges from 12 to 40 V. Low inductance, especially in combination with a high supply voltage, enables high stepping rates. However, to give the same torque capability at low speed, the reduced number of turns in the winding of the low resistive, low inductive motor must be compensated by a higher current. A compromise has to be made. Choose a motor with the lowest possible winding resistance and inductance, 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 max. current. General Phase inputs A logic HIGH on a Phase input gives a current flowing from pin MA into MB. A logic LOW gives a current flow in the opposite direction. A time delay prevents cross conduction in the H-bridge when changing the Phase input. Heat sinking Soldering the batwing ground leads onto a copper ground plane of 20 cm2 (approx. 1.8" x 1.8"), copper foil thickness 35 µm, permits the circuit to operate with 650 mA output current, both channels driving, at ambient temperatures up to 70°C. Consult figures 7,10 and 11 in order to determine the necessary copper ground plane area for heat sinking at higher current levels. Thermal shutdown The circuit is equipped with a thermal shutdown function that turns the output off at temperatures above 160°C. Normal operation is resumed when the temperature has decreased. Phase 1 Dis 1 80 Phase 2 Thermal resistance [°C/W] Dis 2 28-Pin PLCC 70 V R1 140% 100% 60 V R2 140% 100% 50 I MA1 140% 40 100% 22-Pin DIP 30 –100% –140% I MA2 20 5 10 15 20 25 30 35 140% 100% PCB copper foil area [cm 2 ] PLCC package DIP package –100% –140% Full step mode Figure 7. Typical thermal resistance vs. PC Board copper area and suggested layout Half step mode Figure 8. Stepping modes Modified half step mode NJM3774 Programming Figure 8 shows the different input and output sequences for full-step, half-step and modified halfstep operations. Full-step mode Both windings are energized at all the time with the same current, IM1 = IM2. To make the motor take one step, the current direction (and the magnetic field direction) in one phase is reversed. The next step is then taken when the other phase current reverses. The current changes go through a sequence of four different states which equal four full steps until the initial state is reached again. Half-step mode In the half-step mode, the current in one winding is brought to zero before a complete current reversal is made. The motor will then have taken two half steps equalling one full step in rotary movement. The cycle is repeated, but on the other phase. A total of eight states are sequenced until the initial state is reached again. Half-step mode can overcome potential resonance problems. Resonances appear as a sudden loss of torque at one or more distinct stepping rates and must be avoided so as not to loose control of the motor´s shaft position. One disadvantage with the half-step mode is the reduced torque in the half step positions, in which current flows through one winding only. The torque in this position is approximately 70 % of the full step position torque. Modified half-step mode. The torque variations in half step mode will be elimi-nated if the current is increased about 1.4 times in the halfstep position. A constant torque will further reduce resonances and mechanical noise, resulting in better performance, life expectancy and reliability of the mechanical system. Modifying the current levels must be done by bringing the reference voltage up (or down) from its nominal value correspondingly. This can be done by using DACs or simple resistor divider networks, as shown in figure 9. The NJM3774 is designed to handle about 1.4 times higher current in one channel on mode, for example 700 mA per winding in the full-step position, and 1000 mA in the half-step position. V Ref +5 V 1.2 kΩ V R1 and V R2 on NJM3774 10 kΩ 1.2 kΩ 2.2 kΩ 10 nF 70 % current level GND Figure 9. Reduction of reference voltage at the VR pin of NJM3774 NJM3774 ■ TYPICAL CHARACTERISTICS PD (W) Maximum allowable power dissipation [W] VCE Sat (V) 6 3.0 5 1.2 4 te 3 ls 1.0 o tu re 0.8 0.6 0.4 1 nel han 0.20 on 0.2 0 -25 0.40 0.60 0 25 PLCC package DIP package Figure 10. Power dissipation vs. motor current,TA = 25°C 50 75 100 125 150 Temperature [°C] 0.80 I M (A) 0 0 All ground pins soldered onto a 20 cm 2 PCB copper area with free air convection. Figure 11. Maximum allowable continuous power dissipation vs. temperature Vd, ld (V) 0.20 0.40 0.60 0.80 I M (A) Figure 12. Typical lower transistor saturation voltage vs. output current VCE Sat (V) 1.2 1.2 1.0 1.0 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 0 0.20 ra 1.0 c c One 0 pe 2 n ha Tw 0 m on ne 0 nt ture pera tem 2.0 bie pin ing Batw Am 0.40 I M (A) 0.60 0.80 0 0 0.20 0.40 0.60 0.80 I M (A) Figure 13. Typical lower diode voltage Figure 14. Typical upper transistor saturation voltage vs. output current drop vs. recirculating current 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.