NJRC NJM3770AFM2 Stepper motor driver Datasheet

NJM3770A
STEPPER MOTOR DRIVER
■ GENERAL DESCRIPTION
NJM3770A 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 NJM3770A is a high power version and pincompatible with the NJM3717.Two NJM3770A and a small
number of external components form a complete control
and drive unit stepper motor systems.
■ PACKAGE OUTLINE
NJM3770AD3
NJM3770AE2
■ EATURES
• Half-step and full-step operation
NJM3770AFM2
• Switched mode bipolar constant current drive
• Wide range of current control 5 -1800 mA
• Wide voltage range 10 - 45 V
• Thermal overload protection
• Packages DIP16 (Batwing) / PLCC28 / EMP20
■ BLOCK DIAGRAM
VMM
VCC
Schmitt
Trigger
VMM
Time
Delay
Phase
1
≥1
≥1
I
MA
1
MB
I0
V
R
&
&
&
≥1
&
+
–
≥1
Output Stage
+
–
Monostable
t off = 0.69 • RT • CT
+
–
GND
Current Sensor
NJM3770A
C
Figure 1. Block diagram
T
E
NJM3770A
GND
GND 6
GND
NJM
3770AE2
7
15
GND
14
GND
GND 4
GND 5
14 VMM
NJM
3770AD3
N/C 5
25 N/C
MA 6
13 GND
24 V R
N/C 7
12 GND
23 C
NJM
3770AFM2
E 8
GND 9
22 N/C
21 I 0
M B 10
VCC 6
11 V R
VCC 8
13
VR
I1 9
12
C
I1 7
10 C
11
I0
Phase 8
9 I0
Phase 10
26 N/C
16
GND 5
VMM 3
27 N/C
GND
20 Phase
T 11
19 I1
V CC 18
17
GND 17
GND 4
15 M A
T 2
1 GND
VMM
28 GND
18
GND 16
VMM 3
2 GND
MA
GND 15
19
GND 14
T 2
16 E
V MM 12
E
GND 13
20
4 V MM
MB 1
MB 1
3 GND
■ PIN CONFIGURATIONS
Figure 2. Pin configurations
■ PIN DESCRIPTION
EMP
DIP
PLCC
Symbol
1
2
1
2
10
11
MB
T
3
3,14
12,4
VMM
4-7,
14-18
4,5,
12,13
1-3,9,
13-17,28
GND
8
9
6
7
18
19
VCC
I1
10
8
20
Phase
11
9
21
I0
12
10
23
C
13
11
24
VR
19
20
15
16
6
8
MA
E
Description
Motor output B, Motor current flows from MA to MB when Phase is high.
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. Pin 3(12) and pin 14(4) should be wired to
gether.
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.
Logic voltage supply normally +5 V.
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%.
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.
Logic input. It controls, together with the I1 input, the current level in the output
stage.
The controllable levels are fixed to 100, 60, 20, 0%.
Comparator input. This input senses the instantaneous voltage across the
sensing resistor, filtered through a RC Network.
Reference voltage. Controls the threshold voltage of the comparator and hence
the output current. Input resistance: typically 6.8 kΩ ± 20%.
Motor output A, Motor current flows from MA to MB when Phase is high.
Common emitter. Connect the Sense resistor between this pin and ground.
NJM3770A
■ FUNCTIONAL DESCRIPTION
The NJM3770A 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 current 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 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.
External recirculation
diodes
2 1
3
R
200 mA/div
1 ms/div
S
Motor Current
0
1
2
Fast Current Decay
3
100µs/div
Time
Slow Current Decay
Figure 3. Output stage with current paths
for fast and slow current decay.
Figure 4. Motor current (IM ),
Vertical : 200 mA/div,
Horizontal: 1 ms/div,
expanded part 100 µs/div.
NJM3770A
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
I0
I1
High level
L
L
100%
Medium level 60%
H L
Low level
L
20%
Zero current
0%
H
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 • 0.080) / 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 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.
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 3 and 4.
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 )
R = Winding resistance
L = Winding inductance
t = time
(see figure 3, 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 3, 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.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 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 improve speed performance in half-stepping mode.
NJM3770A
■ ABSOLUTE MAXIMUM RATINGS
Parameter
Pin no. [DIP package]
Symbol
Min
Max
Unit
0
7
V
Voltage
Logic supply
6
VCC
Motor supply
3, 14
VMM
0
45
V
Logic inputs
7,8,9
VI
-0.3
6
V
Comparator input
10
VC
-0.3
VCC
V
Reference input
11
VR
-0.3
15
1, 15
IM
-1800
+1800
mA
Current
Motor output current
Logic inputs
7,8,9
II
-10
-
mA
Analog inputs
10,11
IA
-10
-
mA
Operating junction temperature
Tj
-40
+150
°C
Storage temperature
Ts
-55
+150
°C
Temperature
■ RECOMMENDED OPERATING CONDITIONS
Parameter
Symbol
Logic supply voltage
Motor supply voltage
Motor output current
Junction temperature
Rise time logic inputs
Fall time logic inputs
Min
VCC
VMM
IM
TJ
tr
tf
4.75
10
-1500
-20
-
VMM
V CC
6 [18]
I IH
I IL
Schmitt
Trigger
1
8
I
7
15
MA
I0
9
1
MB
VR
11
≥1
≥1
≥1
& & & &
IM
I OL
t on
VI
VA
V IH
V
V IL
t
Output Stage
VM
+
–
td
MA
Monostable
t off = 0.69 • R T• C T
+
–
4, 5,
12, 13
VE
V MM
V
R
GND
t off
1/2
≥1
+
–
VCC
V
V
mA
°C
µs
µs
Normalized
1
IA
5.25
40
+1500
+125
2
2
| V MA – V MB |
VMM
Phase
1
Unit
14
3
Time
Delay
Max
5
-
I MM
I CC
II
Typ
V
CH
Current Sensor
10
IC
C
2
16
T
E
NJM3770A
V
CM
1k
IA
V
RC
VE
VC
820 pF
CC
820 pF
56 k
RT
CT
0.5
R
Pin no. refers
to DIP-package
CL
t
S
1
f=
s t +t
on
off
Figure 5. Definition of symbols
D=
ton
t on + t off
Figure 6. Definition of terms
NJM3770A
■ ELECTRICAL CHARACTERISTICS
Electrical characteristics over recommended operating conditions. CT = 820 pF, RT = 56 kohm
Parameter
Symbol
General
Supply current
ICC
Total power dissipation
PD
Turn-off delay
Thermal shutdown junction temperature
td
Logic Inputs
Logic HIGH input voltage
Logic LOW input voltage
Logic HIGH input current
Logic LOW input current
VIH
VIL
IIH
IIL
Analog Inputs
Comparator threshold voltage
Comparator threshold voltage
Comparator threshold voltage
Input current
VCH
VCM
VCL
IC
Motor Outputs
Lower transistor saturation voltage
VMM = 20 to 40 V, I0 = I1 = HIGH.
VMM = 20 to 40 V, I0 = I1 = LOW,
fs = 23 kHz
fs = 28 kHz, IM = 1.0A, VMM = 36 V
Note 2, 4.
fs = 24 kHz, IM = 1.0A, VMM = 12 V
Note 2, 4.
fs = 28 kHz, IM = 1.3A, VMM = 36 V
Note 3, 4.
fs = 28 kHz, IM = 1.5A, VMM = 36 V
Note 3, 4.
Ta = +25°C, dVC/dt ≥ 50 mV/µs.
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
IM = 1.0A
IM = 1.3A
IM = 1.0A
IM = 1.3A
IM = 1.0A
IM = 1.3A
I0 = I1 = HIGH, Ta = +25°C
Lower diode forward voltage drop
Upper transistor saturation voltage
Output leakage current
Monostable
Cut off time
Conditions
toff
VMM = 10 V, ton ≥ 5 µs
Min
Typ
Max
Unit
-
30
48
40
65
mA
mA
-
1.9
2.3
W
-
1.7
2.1
W
-
2.7
3.2
W
-
3.5
-
W
-
170
2.5
-
µs
°C
2.0
-0.4
-
0.8
20
-
V
V
µA
mA
400
240
70
-20
415
250
80
-
430
265
90
-
mV
mV
mV
µA
-
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
V
V
V
V
V
V
µA
27
31
35
µs
Min
Typ
Max
Unit
-
11
40
9
35
11
40
-
°C/W
°C/W
°C/W
°C/W
°C/W
°C/W
■ THERMAL CHARACTERISTICS
Parameter
Symbol
Thermal resistance
RthJ-GND
RthJ-A
RthJ-GND
RthJ-A
RthJ-GND
RthJ-A
Conditions
DIP package.
DIP package. Note 2.
PLCC package.
PLCC package. Note 2.
EMP package.
EMP package.
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. 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
NJM3770A
■ 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 regulation, interference-generation 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 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.
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 pullout.
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.
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 3,
to obtain a switching frequency above the audible range. Switching frequencies above 40 kHz are not recommended because the current regulation can be affected.
VCC (+5V)
V MM
11
Phase
8
A
I 1A
I
0A
Phase
7
I1
9
I0
T
V
R
6
V
CC
V
MM
C
56 k
E
1k
8
7
9
V MM
V
Phase R
I1
3,14
V
CC
GND
2
56 k
6
V
MM
NJM3770A
I0
T
820pF
0.5
820pF
11
I 1A
I
0A
15
A
16
VCC (+5V)
A
M
10
4, 5
12, 13
820pF
Phase
1
M
B
NJM3770A
GND
2
STEPPER
MOTOR
3,14
4, 5
12, 13
C
M
B
1
M 15
A
E
10
16
1k
820pF
0.5
Diodes are
UF 4001 or
BYV27
t ≤ 100 ns
Figure 7. Typical stepper motor driver application with NJM3770A
NJM3770A
Analog control
As the current levels can be continuously controlled by modulating the VR input, limited microstepping can be
achieved.
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. Ultra-fast recovery diodes should be
used for maximum performance and reliability.
I 0A
I 1A
Ph A
Thermal resistance [°C/W]
Ph B
90
16-pin
DIP
80
I 0B
I 1B
I MA
70
100%
60%
60
–20%
–60%
–100%
50
20-pin
EMP
I MB
100%
60%
20%
40
30
5
10
15
20
25
30
–60%
–100%
35
PCB copper foil area [cm 2 ]
PLCC package
DIP package
Full step position
28-pin
PLCC
Half step position
Stand by mode
at 20 %
Figure 8. Copper foil used as a heatsink
Half step mode at 100 %
Figure 9. Principal operating sequence.
Full step mode at 60 %
NJM3770A
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 NJM3770A 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 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 14 and 15 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.
33,5 mm
11,6 mm
38,5 mm
18,5 m
m
mm
38.0
Figure 10. Heatsinks, Staver, type V7 and V8
by Columbia-Staver UK
mm
38.0
NJM3770A
■ TYPICAL CHARACTERISTICS
VSat (V)
VF (V)
VSat (V)
1.8
1.8
1.8
1.6
1.6
1.4
1.4
1.2
1.2
1.6
Tj = 25 °C
1.4
1.2
Tj = 125°C
1.0
1.0
.8
.8
.6
.6
.4
.4
.4
.2
.2
.2
Tj = 25°C
1.0
.8
Tj = 125°C
.6
0
0
.40
.80
1.2
1.6
0
0
.40
.80
Figure 11. Typical source saturation
vs. output current
PD (W)
1.2
1.6
I M (A)
I M (A)
Figure 12. Typical lower diode
voltage drop vs. recirculating current
0
Tj = 125°C
Tj = 25°C
0
.40
.80
1.2
1.6
I M (A)
Figure 13. Typical sink saturation
vs. output current
PD (W)
VMM = 36 V
3.0
4.0
2.0
B
er
he
V8
at
(3
sin
7.
k(
5°
C/
W
)
40
°C
/W
)
)
W
C/
1.0
av
5°
2.0
VMM = 12 V
PC
7.
(2
1.5
St
V7
er
av
St
3.0
ith
ith
W
2.5
W
1.0
.5
0
0
.50
1.0
1.5
I M (A)
Figure 14. Typical power dissipation
vs. motor current
0
50
100
150
TAmb (°C)
Figure 15. Allowable power dissipation
vs. ambient temperature
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.
Similar pages