NJM37770 - 1 - ver.2006-04-11 stepper motor driver general description package outline NJM37770 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 NJM37770 is a high power version and pincompatible with the njm37717 and also NJM37770 is a high voltage version with njm3770a . two NJM37770 and a small number of external components form a complete control and drive unit stepper motor systems. features half-step and full-step operation switched mode bipolar constant current drive wide range of current control 5 to 1500ma wide voltage range 10 to 60 v thermal overload protection packages dip16 (batwing) / emp20 block diagram figure 1. block diagram NJM37770d3 NJM37770e2
NJM37770 - 2 - ver.2006-04-11 pin configuration figure 2. pin configuration pin description dip emp symbol description 1 1 m b motor output b, motor current flows from m a to m b when phase is high. 2 2 t clock oscillator. timing pin connect a 56 k ? resistor and a 820 pf in parallel between t and ground. 3,14 3,18 v mm motor supply voltage, 10 to 40 v. pin 3 and pin 14(emp pin 18) should be wired to gether. 4,5, 12,13 4-7 14-17 gnd ground and negative supply. note t hese pins are used for heatsinking. make sure that all ground pins are soldered onto a suitable large copper ground plane for efficient heat sinking. 6 8 v cc logic voltage supply normally +5 v. 7 9 i 1 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%. 8 10 phase controls the directi on of the motor current of m a and m b outputs. motor current flows from m a to m b when the phase input is high. 9 11 i 0 logic input. it controls, together with the i 1 input, the current level in the output stage. the controllable levels are fixed to 100, 60, 20, 0%. 10 12 c comparator input. this input senses the instantaneous voltage across the sensing resistor, filtered through a rc network. 11 13 v r reference voltage. controls the thre shold voltage of the comparator and hence the output current. input resistance: typically 6.8 k ? 20%. 15 19 m a motor output a, motor current flows from m a to m b when phase is high. 16 20 e common emitter. connect the sens e resistor between this pin and ground.
NJM37770 - 3 - ver.2006-04-11 functional description the NJM37770 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 curr ent 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 m a to m b and low input from terminal m b to m a . a schmitt trigger provides noise imm unity and a delay circuit eliminates the risk of cross conduction in th e output stage during a phase shift. half- and full-step operation is possible. figure 3. output stage with curren t pathsfor fast and slow curren t decay. figure 4. motor current (i m ), vertical : 200 ma/div, horizontal: 1 ms/div, expanded part 100 s/div.
NJM37770 - 4 - ver.2006-04-11 current level selection. the status of i 0 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 i 0 i 1 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 v r together with the value of the sensing resistor r s . the peak motor current can be calculated as follows: i m = (v r ? 0.080) / r s [a], at 100% level the motor current can also be continuously vari ed 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 cu rrent sensing resistor, r s , 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 tri ggered on the positive edge of the comparator output. the multivibrator output is high during the pulse time, t off , which is determined by the timing components r t and c t . t off = 0.69 ? r t ? c t the single pulse switches off the power feed to the motor winding, causing the winding to decrease during t off . if a new trigger signal should occur during t off , it is ignored. output stage the output stage contains four transistors and two diodes, c onnected 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, whic h will limit the junction temperature. the output current will be reduced if the maximum permissible junction temperature is exceeded. it shou ld 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: i m = (v mm / 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, r s , as an analog voltage. this voltage is fed through a low-pass filter, r c c c , to the voltage comparator input (dip pin 10, emp pin 12). 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 moto r winding reverses and the current is fo rced 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 decay ed 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 i 1 and i 0 are high, all four transistors in the output h-bridge are turned off, which means that induc tive 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 im prove speed performance in half-stepping mode.
NJM37770 - 5 - ver.2006-04-11 absolute maximum ratings parameter pin no. [dip package] symbol min max unit voltage logic supply 6 v cc 0 7 v motor supply 3, 14 v mm 0 60 v logic inputs 7,8,9 v i -0.3 6 v comparator input 10 v c -0.3 v cc v reference input 11 v r -0.3 15 v current motor output current 1, 15 i m -1500 +1500 ma logic inputs 7,8,9 i i -10 - ma analog inputs 10,11 i a -10 - ma temperature operating junction temperature t j -40 +150 c storage temperature t s -55 +150 c recommended operating conditions (t a =25c) parameter symbol min typ max unit logic supply voltage v cc 4.75 5 5.25 v motor supply voltage v mm 10 - 55 v motor output current i m -1300 - +1300 ma junction temperature t j -20 - +125 c rise time logic inputs t r - - 2 s fall time logic inputs t f - - 2 s figure 5. definition of symbols figure 6. definition of terms
NJM37770 - 6 - ver.2006-04-11 electrical characteristics electrical characteristics over recommended oper ating conditions, unless otherwise specified.t a =25c c t =820pf, r t =56k ? parameter symbol conditions min typ max unit general supply current i cc v mm =20 to 55v, i 0 =i 1 =high. - 30 40 ma v mm =20 to 55v, i 0 =i 1 =low, f s =23khz - 48 65 ma total power dissipation p d f s =28khz, i m = 1.0a, v mm = 36v note 2, 4. - 1.9 2.3 w f s =24khz, i m =1.0a, v mm =12v note2, 4. - 1.7 2.1 w f s =28khz, i m =1.3a, v mm =36v note3, 4. - 2.7 3.2 w f s =28khz, i m =1.5a, v mm =36v note3, 4. - 3.5 - w f s =28khz, i m =1.0a, v mm =48v note3, 4. - 3.5 - w turn-off delay t d dv c /dt 50mv/s. v mm =48v, r l =200 ? - 2.0 2.3 s thermal shutdown junction temperature - 165 - c logic inputs logic high input voltage v ih 2.0 - - v logic low input voltage v il - - 0.8 v logic high input current i ih v i =2.4v - - 20 a logic low input current i il v i =0.4v -0.4 - - ma analog inputs comparator threshold voltage v ch v r =5.0v, i 0 =i 1 =low 400 415 430 mv comparator threshold voltage v cm v r =5.0v, i 0 =high, i 1 =low 240 250 265 mv comparator threshold voltage v cl v r =5.0v, i 0 =low, i 1 =high 70 80 90 mv input current i c -20 - - a motor outputs lower transistor saturation voltage i m =1.0a - 0.5 0.8 v i m =1.3a - 0.8 1.3 v lower diode forward voltage drop i m =1.0a - 1.3 1.6 v i m =1.3a - 1.5 1.8 v upper transistor saturation voltage i m =1.0a - 1.1 1.3 v i m =1.3a - 1.3 1.6 v output leakage current i 0 =i 1 =high - - 100 a monostable cut off time t off v mm =10v, t on 5s 27 31 35 s thermal characteristics parameter symbol conditions min typ max unit thermal resistance rth j-gnd dip package. - 11 - c/w rth j-a dip package. note 2. - 40 - c/w rth j-gnd emp package - 11 - c/w rth j-a emp package - 40 - 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 cm 2 pcb copper area with free air convection t a =+25c 3. dip package with external heatsink (sta ver v7) and minimal copper area. typical rth j-a =27.5c/w. t a =+25c 4. not covered by final test program
NJM37770 - 7 - ver.2006-04-11 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 regulat ion, interference-generation problems can arise in some applications. a good measure is t hen to decouple the circuit with a 0.1 f ce ramic capacitor, located near the package across the power line v mm and ground. also make sure that the v ref input is sufficiently decoupled. an electr olytic capacitor should be used in the +5v rail, close to the circuit. the ground leads between r s , c c and circuit gnd should be kept as short as possible. this applies also to the leads connecting r s and r c to pin 16 and pin 10 respectively. in order to minimize electromagnetic inte rference, it is recommended to route m a and m b leads in parallel on the printed circuit board directly to the terminal connector. the motor wi res 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 hi ghest possible noise immunity. ramping a stepper motor is a synchronous motor and does not change it s speed due to load variations. this means that the torque of the motor must be large enough to match the combi ned inertia of the motor and load for all operation modes. at speed changes, the requires torque increases by the squar e, and the required power by the cube of the speed change. ramping, i.e., controlled acceleration or decelerati on must then be considered to avoid motor pullout. v cc , v mm 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, al l 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, t off , determines the switching frequency of the current regulator. the choice of motor may then require other values on the r t , c t components than those recommended in figure 3, to obtain a switching frequency above the audible range. switchin g frequencies above 40 khz are not recommended because the current regulation can be affected. figure 7. typical stepper motor driver application with NJM37770
NJM37770 - 8 - ver.2006-04-11 analog control as the current levels can be conti nuously controlled by modulating the v r input, limited microstepping can be achieved. sensor resistor the r s 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 v r = 5v. the peak motor current, i m , can be calculated by using the formula: i m =(v r ? 0.080) / r s [a], at 100% level external recirculation diodes recirculation diodes must be connected across each motor terminal and the supply voltage, v mm . the anodes shall be connected to the motor terminals and the cathodes to the v mm voltage. ultra-fast recovery diodes should be used for maximum performance and reliability. figure 8. copper foil used as a heatsink figure 9. principal operating sequence.
NJM37770 - 9 - ver.2006-04-11 heatsinking the junction temperature of the chip highly effects the lifetime of the circuit. in high-curr ent applications, the heatsinking must be carefully considered. the rth j-a of the NJM37770 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 cm 2 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 th e required heatsinking of the circuit. in some systems, forced-air cooling may be available to reduce the temperature rise of the circuit. a) staver v7 b) staver v8 figure 10. heatsinks, staver, type v7 and v8 by columbia-staver uk
NJM37770 - 10 - ver.2006-04-11 typical characteristics figure 11. typical source saturation vs. output current figure 12. typical lower diode voltage drop vs. recirculating current figure 13. typical sink saturation vs. output current figure 14. typical power dissipation vs. motor current figure 15. allowable power dissipation vs. ambient temperature [caution] 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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