April 1997 PBL 3717/2 PBL 3717/2 Stepper Motor Drive Circuit Description Key Features PBL 3717/2 is a bipolar monolithic circuit intended to control and drive the current in one winding of a stepper motor. The circuit 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. Two PBL 3717/2 and a small number of external components form a complete control and drive unit for LS-TTL or microprocessor-controlled stepper motor systems. • Half-step and full-step modes. • Switched mode bipolar constant current drive. • Wide range of current control 5 - 1200 mA. • Wide voltage range 10 - 50 V. • Designed for unstabilized motor supply voltage. • Current levels can be selected in steps or varied continuously. PB L3 71 7/ 2 • Thermal overload protection. VMM VCC Schmitt Trigger Time Delay 1 1 16-pin plastic batwing DIP 1 I1 L B /2 P 17 37 Phase VMM MA MB I0 VR & & & ≥1 & + – ≥1 L PB Monostable t = 0.69 • R • C off T T + – PBL 3717/2 Current Sensor C 2 Output Stage + – GND 28-pin plastic PLCC package T 7/ 1 7 3 20-pin SO wide batwing package E Figure 1. Block diagram. 1 PBL 3717/2 Maximum Ratings Parameter * Symbol Min Max Voltage Logic supply Motor supply 6 3, 14 VCC VMM 0 0 7 50 V V Logic inputs Comparator input Reference input 7, 8, 9 10 11 VI VC VR -0.3 -0.3 -0.3 6 VCC 15 V V V Current Motor output current Logic inputs 1, 15 7, 8, 9 IM II -1200 -10 +1200 10, 11 IA -10 TJ TS -40 -55 +150 +150 Analog inputs Temperature Operating temperature Storage temperature Unit mA mA mA °C °C * refers to DIP package Recommended Operating Conditions Parameter Symbol Min Typ Max Logic supply voltage VCC 4.75 5 5.25 Motor supply voltage Motor output current Junction Temp VMM IM TJ 10 -1000 -20 Rise time logic inputs Fall time logic inputs tr tf I I I I I IH IL 8 I 7 I IA 1 V CC V V 6 14 3 MM Time Delay 1 1 0 9 11 & & & ≥1 & ≥1 + – V CC VI V V IH VA 4, 5, GND 12, 13 V Monostable t = 0.69 • R • C off T T PBL 3717/2 10 2 16 C T E 1 kΩ Pin no. refers to DIP package IA R VC VCH 820 pF CC 2 MB V Current Sensor IC I OL Output Stage + – IL IM 1 + – V R Figure 2. Definition of symbols. MA 15 VR MM MM 1 C VE 820 pF 56 kΩ 1Ω R T C T R S M MA V mA °C µs µs 2 2 I Phase V 40 +1000 +125 CC Schmitt Trigger Unit V MM PBL 3717/2 Electrical Characteristics Electrical characteristics over recommended operating conditions. unless otherwise noted -20°C≤ TJ≤ +125°C. CT = 820 pF, RT = 56 kohm. Parameter Ref. Symbol fig. Conditions General Supply current Total power dissipation ICC PD fs = 28 kHz, IM = 500 A, VMM = 36 V Turn-off delay td 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 Min Typ Max Unit 1.4 25 1.7 mA W 2.8 3.3 W 0.9 170 1.5 µs °C 2 3 VIH VIL 2 2 IIH IIL 2 2 RR Note 2, 4. fs = 28 kHz, IM = 800 A, VMM = 36 V Note 3, 4. Ta = +25°C, dVC/dt ≥ 50 mV/µs. 2.0 0.8 VI = 2.4 V VI = 0.4 V 20 -0.4 Ta = +25°C 6.8 V V µA mA kohm VCH VCM 2 2 VR = 5.0 V, I0 = I1 = LOW VR = 5.0 V, I0 = HIGH, I1 = LOW 400 240 415 250 430 265 mV mV VCL IC 2 2 VR = 5.0 V, I0 = LOW, I1 = HIGH 70 -20 80 90 mV µA Lower transistor saturation voltage 2 Lower diode forward voltage drop 2 Upper transistor saturation voltage 2 IM = 500 mA IM = 800 mA IM = 500 mA IM = 800 mA IM = 500 mA IM = 800 mA 0.9 1.1 1.2 1.3 1.0 1.2 1.2 1.4 1.5 1.7 1.25 1.5 V V V V V V Upper diode forward voltage drop 2 1.0 1.2 Output leakage current Monostable Cut off time 2 IM = 500 mA IM = 800 mA I0 = I1 = HIGH, Ta = +25°C 1.25 1.45 100 V V µA 3 VMM = 10 V, ton ≥ 5 µs 27 31 35 µs Min Typ Max Threshold voltage Input current Motor Outputs toff Thermal Characteristics Parameter Thermal resistance Notes 1. All voltages are with respect to ground. Currents are positive into, negative out of specified terminal. Ref. Symbol Fig. Conditions Rthj-c Rthj-a 16 DIP package. DIP package. Note 2. 11 40 °C/W °C/W Rthj-c Rthj-a 16 Rthj-c PLCC package. PLCC package. Note 2. SO package 9 35 11 °C/W °C/W °C/W Rthj-a SO package 40 °C/W 2. All ground pins soldered onto a 20 cm 2 PCB copper area with free air convection. TA +25°C. Unit 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. 3 13 PBL 3717/2N 12 18 V MM GND 4 17 GND GND 5 GND GND 6 GND 7 11 VR I1 7 10 C Phase 8 9 I0 26 N/C 27 N/C 1 GND 28 GND 2 GND 3 GND 25 N/C MA 6 24 V R 23 C N/C 7 GND VCC 6 N/C 5 VCC 8 PBL 3717/2 16 GND E 8 15 GND GND 9 14 GND M B 10 13 V R I1 9 12 C Phase 10 11 I 0 PBL 3717/2QN 22 N/C 21 I 0 20 Phase T 11 19 I1 V CC 18 GND 5 VMM 14 19 M A VMM 3 GND 17 GND 4 MA GND 16 VMM 3 20 E T 2 GND 15 15 MB 1 GND 14 T 2 E V MM 12 16 GND 13 MB 1 4 V MM PBL 3717/2 Figure 3. Pin configurations. Pin Description DIP SO PLCC Symbol Description 1 1 10 MB Motor output B, Motor current flows from MA to MB when Phase is high. 2 2 11 T 3,14 3,18 12,4 VMM 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. VMM pins should be wired together on PCB. 4,5, 12,13 4,5,6,7,14 15,16,17 1,2,3,9,13, 14,15,16,17 28 GND 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. 6 8 18 VCC Logic voltage supply normally +5 V. 7 9 19 I1 Logic input, it controls, together with the I0 input, the current level in the output stage. The controlable levels are fixed to 100, 60, 20, 0%. 8 10 20 Phase 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. 9 11 21 I0 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%. 10 12 23 C Comparator input. This input senses the instaneous voltage across the sensing resistor, filtered through a RC Network. 11 13 24 VR Reference voltage. Controls the threshold voltage of the comparator and hence the output current. Input resistance: typically 6.8kΩ ± 20%. 15 19 6 MA Motor output A, Motor current flows from MA to MB when Phase is high. 16 20 8 E Common emitter. Connect the sence resistor between this pin and ground. 4 PBL 3717/2 Functional Description The PBL 3717/2 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 5 and 6. 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 | V MA – V MB | t on t off 50 % t VE td V CH Input logic t 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. High level I0 100% L ton ton + t off Figure 4. Definition of terms. 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. I1 L 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. Medium level 60% H L Single-pulse generator Low level L H 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 20% D= Current sensor 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 1 f s= t + t on off 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 = (VR • 0.083) / RS [A], at 100% level im = (VR • 0.050) / RS [A], at 60% level im = (VR • 0.016) / RS [A], at 20% level The motor current can also be continuously varied by modulating the voltage reference input. 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 Hbridge. 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 5 and 6. 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 6, 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 6, 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. 5 PBL 3717/2 1 200 mA/div 1 ms/div 0 3 100 µs/div R Figure 5. Motor current (I M ),Vertical : 200 mA/div, Horizontal: 1 ms/div, expanded part 100 µs/div. 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 S 2 Fast Current Decay Slow Current Decay 3 Time Figure 6. Output stage with current paths for fast and slow current decay. Phase shift here gives fast current decay Phase shift here gives slow current decay I 0A I 1A Ph A Ph B I 0B I 1B I MA 100% 60% –20% –60% –100% I MB 100% 60% 20% –60% –100% Full step position Half step position Stand by mode at 20% Half step mode at 100 % Figure 7. Principal operating sequence. 6 Motor Current 1 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 PBL 3717/2 can be reduced by soldering the ground pins to a suitable copper ground plane on the printed circuit board (see figure 16) or by applying an external heatsink type V7 or V8, see figure 15. The diagram in figure 14 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 500 mA, heatsinking is recommended to assure optimal reliability. The diagrams in figures 13 and 14 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. 2 913001 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 6, arrow 4). 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 currentinhibiting signal is applied (see figure 2). Full step mode at 60 % PBL 3717/2 11 Phase 8 A V Phase R 7 I 9 1 I 0 T I 1A I 0A operation. Some stepper motors have such high core losses that they are not suited for switched-mode operation. VMM VCC (+5 V) 6 3, 14 CC V 1 MM M B V PBL 3717/2 C GND STEPPER MOTOR Interference M 15 A E VSat (V) VSat (V) 1.8 1.8 1.6 1.6 As the circuit operates with switchedmode current regulation, interferencegeneration 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 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. 1.4 Unused inputs 2 4, 5 10 12, 13 56 kΩ 16 1 kΩ 1Ω 820 pF 820 pF V (+5 V) CC V 6 11 MM 3, 14 V V V 8 1 CC MM M Phase R B 7 I 1 9 PBL 3717/2 I M 15 0 A Phase B I 1B I 0B T GND 2 C E 4, 5 10 12, 13 56 kΩ 16 Pin no refers to DIP package 1 kΩ 820 pF 820 pF 1Ω Figure 8. Typical stepper motor driver application with PBL 3717/2. 1.4 Tj = 125 °C 1.2 1.2 1.0 Tj = 25 °C .8 .8 .6 .6 .4 .4 .2 .2 0 0 0 .20 .40 .60 .80 Tj = 25 °C 1.0 Tj = 125 °C Ramping 0 .20 Figure 9. Typical source saturation vs. output current. .40 .60 .80 1.0 I M (A) I M (A) Figure 10. Typical sink saturation vs. output current. VF (V) VF (V) 1.8 1.8 1.6 1.6 1.4 1.4 Tj = 25°C 1.2 1.0 1.0 Tj = 125°C .8 .6 .6 .4 .4 .2 .2 0 .20 .40 Tj = 25°C 1.2 .8 0 Unused inputs should be connected to proper voltage levels in order to obtain the highest possible noise immunity. 1.0 .60 .80 1.0 I M (A) Figure 11. Typical lower diode voltage drop vs. recirculating current. 0 Tj = 125°C 0 .20 .40 .60 .80 1.0 I M (A) 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 pull-out. 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 from being generated by the motor. Figure 12. Typical upper diode voltage drop vs. recirculating current. 7 PBL 3717/2 Analog control PD (W) ith St av er (3 at 5° C/ W ) 3 .5 40 °C 7 (2 sin k( /W °C 2.0 4 V7 he 7. er av B St V8 PC 3.0 ith /W ) 2 ) Sensor resistor 5 W W 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 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. 4.0 PD (W) 1.0 1 0 50 0 150 100 0 TAmb (°C) .40 .60 .80 Figure 13. Typical power dissipation vs. motor current. 40.6 m m 17.0 m 34.3 mm m im = (VR • 0.083) / RS [A], at 100% level im = (VR • 0.050) / RS [A], at 60% level im = (VR • 0.016) / RS [A], at 20% level Ordering Information Package Plastic DIP PLCC SO 38.0 Part No. PBL 3717/2N PBL 3717/2QN PBL 3717/2SO mm 38.0 Figure 15. Heatsinks, Staver, type V7 and V8 by Columbia-Staver UK. Thermal resistance [°C/W] 90 Information given in this data sheet is believed to be accurate and reliable. However no responsibility is assumed for the consequences of its use nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Ericsson Components. These products are sold only according to Ericsson Components' general conditions of sale, unless otherwise confirmed in writing. Specifications subject to change without notice. IC4 (88076) C-Ue © Ericsson Components AB 1997 16-pin DIP 80 70 60 50 20-pin SO 40 30 5 10 15 20 25 30 35 PCB copper foil area [cm2 ] Ericsson Components AB S-164 81 Kista-Stockholm, Sweden Telephone: (08) 757 50 00 8 1.0 I M (A) Figure 14. Allowable power dissipation vs. ambient temperature. The RS resistor should be of a noninductive type, power resistor. A 1.0 ohm resistor, tolerance ≤ 1%, is a good choice for 415 mA max motor current at VR = 5V. Thepeak motor current, im , can be calculated by using the formulas: .20 11.9 mm As the current levels can be continuously controlled by modulating the VR input, limited microstepping can be achieved. PLCC package DIP and SO package Figure 16. Copper foil used as a heatsink. 28-pin PLCC mm