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February 1999
PBL 3770A High Performance Stepper Motor Drive Circuit
Description
PBL 3770A is a bipolar monolithic circuit intended to control and drive the current in one winding of a stepper motor. It is a high power version of PBL 3717 and special care has been taken to optimize the power handling capability without suffering in reliability. 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. The circuit is pin-compatible with the PBL 3717 industry-standard driver. Two PBL 3770A and a small number of external components form a complete control and drive unit for LS-TTL or microprocessor-controlled stepper motor systems.
Key Features
* Half-step and full-step operation. * Switched mode bipolar constant current drive * Wide range of current control 5 -1800 mA. * Wide voltage range 10 - 45 V. * Designed for unstabilized motor supply voltage. * Current levels can be selected in steps or varied continuously. * Thermal overload protection.
VCC
Schmitt Trigger Time Delay
VMM
VMM
Phase I
1
1
1
1
P
B
L BA P 70 37
MA I0 V
R
MB
&
+ - + - + - GND
&
&
&
1
1
L
Monostable t off = 0.69 * RT * CT Current Sensor
37
PBL 3770A
C T E
16-pin plastic batwing DIP 28-pin plastic PLCC package 20-pin SO
Figure 1. Block diagram.
1
P
B
L
37
Output Stage
70
A
70
A
PBL 3770A
Maximum Ratings
Parameter Pin no. [DIL package] Symbol Min Max Unit
Voltage Logic supply Motor supply Logic inputs Comparator input Reference input Current Motor output current Logic inputs Analog inputs Temperature Operating junction temperature Storage temperature
6 3, 14 7,8,9 10 11 1, 15 7,8,9 10,11
VCC VMM VI VC VR IM II IA TJ Ts
0 0 -0.3 -0.3 -0.3 -1800 -10 -10 -40 -55
7 45 6 VCC 15 +1800
V V V V V mA mA mA C C
+150 +150
Recommended Operating Conditions
Parameter Symbol Min Typ Max Unit
Logic supply voltage Motor supply voltage Motor output current Junction temperature Rise time logic inputs Fall time logic inputs
VCC VMM IM TJ tr tf
4.75 10 -1500 -20
5
5.25 40 +1500 +125 2 2
V V mA C s s
I CC
I MM
V CC
6 [18] Schmitt Trigger Time Delay
VMM
3
VMM
14
II
I IH
I IL
Phase I
8 7
1
1
1
15
MA
IM
I OL
1 9 11 1
I0 IA VR
MB
&
+ - VCC VI V IH V IL VA V
R
&
&
&
1
1
Output Stage
+ - + - GND
4, 5, 12, 13 10 Current Sensor 2 16 Monostable t off = 0.69 * R T* C T
VM V
MA
V MM
PBL 3770A
IC IA
C
1k
T
E
RC VC
820 pF 56 k 820 pF 0.5
VE RT R
Pin no. refers to DIL-package
CC
CT
S
Figure 2. Definition of symbols.
2
PBL 3770A
Electrical Characteristics
Electrical characteristics over recommended operating conditions. CT = 820 pF, RT = 56 kohm.
Parameter Ref. Symbol fig. Conditions Min Typ Max Unit
General Supply current
ICC
2
Total power dissipation
PD
Turn-off delay td 3 Thermal shutdown junction temperature Logic Inputs Logic HIGH input voltage Logic LOW input voltage Logic HIGH input current Logic LOW input current Analog Inputs Comparator threshold voltage Comparator threshold voltage Comparator threshold voltage Input current VIH VIL IIH IIL VCH VCM VCL IC 2 2 2 2 2 2 2 2
VMM = 20 to 40 V, I0 = I1 = HIGH. VMM = 20 to 40 V, I0 = I1 = LOW, fs = 23 kHz fs = 28 kHz, IM = 1000 mA, VMM = 36 V Note 2, 4. fs = 24 kHz, IM = 1000 mA, VMM = 12 V Note 2, 4. fs = 28 kHz, IM = 1300 mA, VMM = 36 V Note 3, 4. fs = 28 kHz, IM = 1500 mA, VMM = 36 V Note 3, 4. Ta = +25C, dVC/dt 50 mV/s.
30 48 1.9 1.7 2.7 3.5
40 65 2.3 2.1 3.2
mA mA W W W W
2.5 170 2.0
s C V V A mA mV mV mV A V V V V V V A s
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
0.8 20 -0.4 400 240 70 -20 415 250 80 430 265 90
Motor Outputs Lower transistor saturation voltage Lower diode forward voltage drop Upper transistor saturation voltage Output leakage current Monostable Cut off time toff 3
IM = 1000 mA IM = 1300 mA IM = 1000 mA IM = 1300 mA IM = 1000 mA IM = 1300 mA I0 = I1 = HIGH, Ta = +25C VMM = 10 V, ton 5 s 27
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 35
31
Thermal Characteristics
Parameter Ref. Symbol Fig. Conditions Min Typ Max Unit
Thermal resistance
RthJ-C DIL package. RthJ-A 15 DIL package. Note 2. RthJ-C PLCC package. RthJ-A 15 PLCC package. Note 2. RthJ-C SO package. RthJ-A 15 SO package.
11 40 9 35 11 40
C/W C/W C/W C/W C/W 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. Ta = +25C. 3. DIP package with external heatsink (Staver V7) and minimal copper area. Typical RthJ-A = 27.5C/W. Ta = +25C. 4. Not covered by final test program. 3
PBL 3770A
3 GND
2 GND
1 GND
28 GND
4 V MM
27 N/C
T2 VMM 3 GDN 4 GDN 5 GDN 6 GDN 7 VCC 8 I1 9 Phase 10
19 M
A
T2 VMM 3 GND 4 GND 5 VCC 6 I1 7 Phase 8
15 M A 14 VMM
N/C 5 MA 6 N/C 7 E8
18 VMM 17 GDN
26 N/C
MB 1
20 E
MB 1
16 E
25 N/C 24 V R
PBL 3770A
16 GDN 15 GDN 14 GDN 13 VR 12 C 11 I 0
PBL 3770A
13 GND 12 GND 11 V R 10 C 9 I0
GND 9 M B 10 T 11
PBL 3770A
23 C 22 N/C 21 I 0 20 Phase 19 I1
V MM 12
GND 13
GND 14
GND 15
GND 16
GND 17
Figure 3. Pin configurations.
Pin Description
SO DIP PLCC Symbol Description
1 2 3 4-7, 14-18 8 9 10 11 12 13 19 20
1 2 3,14 4,5, 12,13 6 7 8 9 10 11 15 16
10 11 12,4 1-3,9, 13-17,28 18 19 20 21 23 24 6 8
Motor output B, Motor current flows from MA to MB when Phase is high. Clock oscillator. Timing pin connect a 56 k resistor and a 820 pF in parallel between T and Ground. VMM Motor supply voltage, 10 to 40 V. Pin 3(12) and pin 14(4) should be wired together. 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. VCC Logic voltage supply normally +5 V. 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%. 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. 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%. C Comparator input. This input senses the instaneous voltage across the sensing resistor, filtered through a RC Network. VR Reference voltage. Controls the threshold voltage of the comparator and hence the output current. Input resistance: typically 6.8 k 20%. MA Motor output A, Motor current flows from MA to MB when Phase is high. E Common emitter. Connect the Sence resistor between this pin and ground.
MB T
4
V CC 18
PBL 3770A
Functional Description
The PBL 3770A 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 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
f= 1 t on 1/2 t off | V MA - V MB |
Normalized
t VE V td
CH
V V
CM
CL
t
s
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. 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 I 0 I 1
1 ton + t off
D=
ton t on + t off
Figure 4. Definition of terms.
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 compara-tor triggers the single-pulse generator. Only one comparator at a time is activa-ted 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 5 and 6. 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
)
High level Medium level Low level Zero current
100% 60% 20% 0%
L H L H
L L H H
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
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
5
PBL 3770A
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 6, 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. 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 3770A can be reduced by soldering the ground pins to a suitable copper ground plane on the printed circuit board (see figure 14) or by applying an external heatsink type V7 or V8, see figure 14. The diagram in figure 13 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 12 and 13 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.
200 mA/div
1 ms/div
External recirculation diodes 21
0
100s/div
3
Figure 5. Motor current (IM ), Vertical : 200 mA/div, Horizontal: 1 ms/div, expanded part 100 s/div.
RS
Motor Current
1
2
3
Fast Current Decay Slow Current Decay
Time
Figure 6. Output stage with current paths for fast and 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 % Full step mode at 60 %
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 highspeed operation. Some stepper motors have such high core losses that they are not suited for switched-mode operation. 6
Figure 7. Principal operating sequence.
PBL 3770A
V C (+5
1 1 R 6 3, 14 M M C V)
VM
M
STEPPER MOTOR
1
Phase AI 1 IA 0 A
8
7e 9
Phas I I
1 0
V
V
C C
V
M
B
PBL 3770A
GN D C
4, 5 12, 13 1 0 1 k 820 pF
M E
T
2
A 1 6
1 5
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 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 being generated by the motor.
1.6
56 k 820 pF
0.5
V C
(+5
1 1 6 3, 14
C V)
VM
M
Phase BI 1 IB 0 B
1 V V V M Phas R C M B e C M I 1 9 PBL 3770A M I 1 0 A5 T GN C E D 4, 5 1 1 2 8 7 12, 13 56 k 820 pF 0 1 k 820 pF 6
0.5
Diodes are UF 4001 or BYV27 t 100 r ns r
Figure 8. Typical stepper motor driver application with PBL 3770A.
VSat (V)
1.8 1.6 1.4 1.2 1.0 .8 .6 .4 .2 0 0 .40 .80 1.2 1.6
VF (V)
1.8 1.6 1.4 1.2
Tj = 25 C Tj = 125C
Tj = 25C Tj = 125C
1.0 .8 .6 .4 .2 0 0 .40 .80 1.2
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 6, to obtain a switching frequency above the audible range. Switching frequencies above 40 kHz are not recommended because the current regulation can be affected. Analog control As the current levels can be continuously controlled by modulating the VR input, limited microstepping can be achieved.
I M (A)
I M (A)
Figure 9. Typical source saturation vs. output current.
VSat (V)
1.8 1.6 1.4 1.2 1.0 .8 .6 .4 .2 0 0 .40 .80
Figure 11. Typical lower diode voltage drop vs. recirculating current.
Interference 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 F 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.
Tj = 125C
Tj = 25C
1.2 1.6
I M (A)
Figure 10. Typical sink saturation vs. output current.
7
PBL 3770A
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. Ultrafast recovery diodes should be used for maximum performance and reliability.
.5 0
0 50 100 150
PD (W)
3.0
2.5 2.0 1.5 1.0
PD (W)
VMM = 36 V
4.0
W
ith
St
av
ith W
3.0
PC
er
V8
av St
B
he
(3
at
7.
sin
2.0
k(
VMM = 12 V
1.0
C/ W ) 40 C /W )
5
er V7 7 (2 .5 ) W C/
0
.50
1.0
1.5
I M (A)
TAmb (C)
Figure 12. Typical power dissipation vs. motor current.
33,5 m m
Figure 13. Allowable power dissipation vs. ambient temperature.
Ordering Information
Package Part No.
18,5 m m
DIP Tube PLCC Tube PLCC Tape & Reel SO Tube SO Tape & Reel
PBL 3770ANS PBL 3770AQNS PBL 3770AQNT PBL 3770ASOS PBL 3770ASOT
38,5 mm
11,6 mm
mm 38.0
mm 38.0
Figure 14. Heatsinks, Staver, type V7 and V8 by Columbia-Staver UK.
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 AB. These products are sold only according to Ericsson Components' general conditions of sale, unless otherwise confirmed in writing.
Thermal resistance [C/W]
90
16-pin DIP
80
70
60
50
Specifications subject to change without notice. 1522-PBL 3770/6Uen. Rev E (c) Ericsson Components AB 1999
20-pin SO
40
30 5 10 15 20 25 30 35
PCB copper foil area [cm 2 ]
PLCC package DIP package
28-pin PLCC
Ericsson Components AB SE-164 81 Kista-Stockholm, Sweden Telephone: +46 8 757 50 00 8
Figure 15. Copper foil used as a heatsink.

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