NJRC NJM3773FM2 Dual stepper motor driver Datasheet

NJM3773
DUAL STEPPER MOTOR DRIVER
■ GENERAL DESCRIPTION
The NJM3773 is a switch-mode (chopper), constant-current
driver with two channels: one for each winding of a two-phase
stepper motor. The NJM3773 is also equipped with a Disable
input to simplify half-stepping operation. The circuit is well
suited for microstepping applications together with an external
micro controller. The current control inputs are low current,
high impedance inputs, which allows the use of unbuffered
DAC or external high resistive resistor divider network. The
NJM3773 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,
including recirculation diodes. Voltage supply requirements
are +5 V for logic and +10 to +45 V for the motor. Maximum
output current is 750mA per channel.
■ PACKAGE OUTLINE
NJM3773D2
NJM3773E3
NJM3773FM2
■ FEATURES
• Dual chopper driver
• 750 mA continuous output current per channel
• High impedance current control inputs
• Digital filter on chip eliminates external filtering components
• Packages DIP22 / PLCC28 / EMP24(Batwing)
■ BLOCK DIAGRAM
Phase 1
Dis1 VR1
E1
C1
NJM3773
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
NJM3773
GND 7
18
GND
VR1 8
17
VR2
C1 9
16
C2
Phase1 10
15
Phase2
Dis1 11
14
Dis2
RC 12
13
Vcc
VMM2
GND 5
GND 6
VR1 7
NJM
3773D2
18
GND
17
GND
16
V R2
C1 8
15
C2
Phase 1 9
14
Phase 2
Dis1 10
13
Dis2
RC 11
12
VCC
26 C 2
GND
NJM
3773E3
19
27 V R2
19
GND 6
VMM1 4
MA2 5
25 Phase 2
E2 6
24 Dis 2
M B2 7
M B1 8
23 VCC
NJM3773FM2
GND 9
22 RC
21 Dis 1
E1 10
20 Phase1
19 C 1
M A1 11
VR1 18
VMM2
GND 17
MA2
20
MA2
1 GND
21
20
28 GND
MA1 4
VMM1 5
MA1 3
GND 16
E2
E2
2 GND
MB2
22
MB2
21
GND 15
23
E1 3
22
E1 2
3 GND
MB1 2
MB1 1
GND 14
NC
GND 13
24
VMM1 12
NC 1
4 VMM2
■ PIN CONFIGURATIONS
Figure 2. Pin configurations
■ PIN DESCRIPTION
EMP
DIP
PLCC
Symbol
2
3
4
5
6,7
18,19
1
2
3
4
5, 6,
17, 18
MB1
E1
MA1
VMM1
GND
8
7
8
10
11
12
1-3, 9,
13-17,
28
18
9
8
19
10
9
20
11
10
21
12
11
22
13
14
12
13
23
24
15
14
25
16
15
26
17
16
27
20
21
22
23
19
20
21
22
4
5
6
7
Description
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 output A, channel 1. Motor current flows from MA1 to MB1 when Phase1 is HIGH.
Motor supply voltage, channel 1, +10 to +40 V. VMM1 and VMM2 should be connected together.
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.
VR1
Reference voltage, channel 1. Controls the comparator threshold voltage and hence the
output current.
C1
Comparator input channel 1. This input senses the instantaneous voltage across the
sensing resistor, filtered by the internal digital filter or an optional external RC network.
Phase1 Controls the direction of motor current at outputs MA1 and MB1. Motor current flows from MA1
to MB1 when Phase1 is HIGH.
Dis1
Disable input for channel 1. When HIGH, all four output transistors are turned off, which
results in a rapidly decreasing output current to zero.
RC
Clock oscillator RC pin. Connect a 12 kohm resistor to VCC and a 4 700 pF capacitor to ground
to obtain the nominal switching frequency of 23.0 kHz and a digital filter blanking time of 1.0µs.
VCC
Logic supply voltage, nominally +5 V.
Dis2
Disable input for channel 2. When HIGH, all four output transistors are turned off, which
results in a rapidly decreasing output current to zero.
Phase2 Controls the direction of motor current at outputs MA2 and MB2. Motor current flows from MA2
to MB2 when Phase2 is HIGH.
C2
Comparator input channel 2. This input senses the instantaneous voltage across the
sensing resistor, filtered by the internal digital filter or an optional external RC network.
VR2
Reference voltage, channel 2. Controls the comparator threshold voltage and hence the
output current.
VMM2
Motor supply voltage, channel 2, +10 to +40 V.VMM1 and VMM2 should be connected together.
MA2
Motor output A, channel 2. Motor current flows from MA2 to MB2 when Phase2 is HIGH.
E2
Common emitter, channel 2. This pin connects to a sensing resistor RS to ground.
MB2
Motor output B, channel 2. Motor current flows from MA2 to MB2 when Phase2 is HIGH.
NJM3773
■ FUNCTIONAL DESCRIPTION
Each channel of the NJM3773 consists of the following sections: an output H-bridge with four transistors and four
recirculation diodes, capable of driving up to 750 mA 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 current-sensing resistor RS, effectively connected in series with the motor
winding. As the current increases, a voltage develops across the sensing resistor, which is fed back to the comparator. At the predetermined level, defined by the voltage at the reference input VR, the comparator resets the flipflop, which turns off the upper output transistor. The turn-off function of the two channels works independently of
each other. The current decreases until the clock oscillator triggers the flip-flops of both channels simultaneously,
which turns on the output transistors again, and the cycle is repeated.
To prevent erroneous switching due to switching transients at turn-on, the
NJM3773 includes a digital filter. The clock oscillator provides a blanking pulse which is used for digital filtering of
the voltage transient across the current sensing resistor during turn-on.
The current paths during constant current switching and phase shift are shown in figure 3.
V MM
1
2
3
RS
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
NJM3773
■ ABSOLUTE MAXIMUM RATINGS
Parameter
Pin no. [DIP]
Symbol
Min
Max
Unit
Voltage
Logic supply
Motor supply
Logic inputs
Analog inputs
12
4, 19
9, 10, 13, 14
7, 8, 15, 16
VCC
VMM
VI
VA
0
0
-0.3
-0.3
7
45
6
VCC
V
V
V
V
Current
Motor output current
Logic inputs
Analog inputs
1, 3, 20, 22
9, 10, 13, 14
7, 8, 15, 16
IM
II
IA
-850
-10
-10
+850
-
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
Max
Unit
■ RECOMMENDED OPERATING CONDITIONS
Parameter
Symbol
Logic supply voltage
Motor supply voltage
Output emitter voltage
Motor output current
Operating junction temperature
Rise and fall time logic inputs
Oscillator timing resistor
VCC
VMM
VE
IM
TJ
tr,, tf
RT
Min
Typ
4.75
10
-750
-20
2
5
12
5.25
40
1.0
+750
+125
2
20
V
V
V
mA
°C
µs
kΩ
| V MA – V MB |
Phase 1
Dis 1 VR1
9
10
7
C1
E1
8
2
t on
NJM3773
t off
50 %
VCC
I CC
—
V
CC
12
+
R
S
Q
Logic
3
M A1
1
M B1
4
V MM1
19
V MM2
22
M B2
20
M A2
t
VE ( I M )
td
12 k‰
+
RT
I MM
V
R
—
Logic
I RC RC
11
+
—
S
R
IM
I OL
Q
4 700 pF
VCC
t
CT
14
Phase 2
II
I IH
I IL
IC
IA
13
16
Dis 2 V
R2
V
V
V
GND
V
21
tb
RC
E2
IA
VC
VA
5, 6, 17, 18
C2
IC
VI
IH
15
VRC
Pin no. refers
to DIP package
VE
A
VM
V MA
V MM
V
IL
R
RB
t
RS
1
fs = t + t
on
off
Figure 4. Definition of symbols
D=
ton
ton + t off
Figure 5. Definition of terms
NJM3773
■ ELECTRICAL CHARACTERISTICS
Electrical characteristics over recommended operating conditions, unless otherwise noted. -20°C ≤ Tj ≤ +125°C.
Parameter
Symbol Conditions
Min
Typ
Max
Unit
General
Supply current
Supply current
Total power dissipation
ICC
ICC
PD
-
55
7
2.0
70
10
2.3
mA
mA
W
Total power dissipation
PD
-
1.7
2.0
W
-
160
1.1
2.0
°C
µs
-0.1
0.6
20
-
V
V
µA
mA
Thermal shutdown junction temperature
Turn-off delay
td
VR=500mV. Note 4.
Dis1= Dis2= HIGH.
VMM= 24 V, IM1= IM2= 500 mA.
Notes 2, 3, 4.
VMM= 24 V, IM1= 700 mA, IM2= 0 mA.
Notes 2, 3, 4.
TA = +25°C, dVC/dt ≥ 50 mV/µs,
IM = 100 mA. Note 3. (one channel on).
Logic Inputs
Logic HIGH input voltage
Logic LOW input voltage
Logic HIGH input current
Logic LOW input current
VIH
VIL
IIH
IIL
VI = 2.4 V
VI = 0.4 V
2.0
-0.2
Analog Inputs
Input current
Threshold voltage
| VC1 - VC2 | mismatch
IA
VC
VC,diff
VR= 500mV
RB= 1 kohm. Note 3.
-0.5
-
-0.2
500
1
-
µA
mV
mV
IM = 500 mA
VMM=41 V,TA = +25°C. Dis1= Dis2= HIGH.
IM = 500 mA
IM = 500 mA.
VMM=41 V,TA = +25°C. Dis1= Dis2= HIGH..
IM = 500 mA.
-
0.4
1.1
1.1
1.1
0.8
100
1.3
1.4
100
1.4
V
µA
V
V
µA
V
CT = 4 700 pF, RT = 12 kohm
CT = 4 700 pF. Note 3.
21.5
-
23.0
1.0
24.5
-
kHz
µs
Motor Outputs
Lower transistor saturation voltage
Lower transistor leakage current
Lower diode forward voltage drop
Upper transistor saturation voltage
Upper transistor leakage current
Upper diode forward voltage drop
Chopper Oscillator
Chopping frequency
Digital filter blanking time
fs
tb
■ THERMAL CHARACTERISTICS
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
Thermal resistance
RthJ-GND
RthJ-A
RthJ-GND
RthJ-A
RthJ-GND
RthJ-A
DIP package.
DIP package. Note 2.
PLCC package.
PLCC package. Note 2.
EMP package
EMP package
-
11
40
9
35
13
42
-
°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 = +25°C.
3. Not covered by final test program.
4. Switching duty cycle D = 30%, fs = 23.0 kHz.
NJM3773
■ APPLICATIONS INFORMATION
Current control
The regulated output current level to the motor winding is determined by the voltage at the reference input and the
value of the sensing resistor, RS. The peak current through the sensing resistor (and the motor winding) can be
expressed as:
IM,peak = VR / RS
[A]
With a recommended value of 0.5 ohm for the sensing resistor RS, a 0.25 V reference voltage will produce an output
current of approximately 500 mA. RS should be selected for maximum motor current. Be should not to exceed the
absolute maximum output current which is 850 mA. Chopping frequency, winding inductance and supply voltage
also affect the current, but to much less extent.
To improve noise immunity on the comparator inputs (VR and C), the control range may be increased to 0.5 V if RS
is correspondingly changed to 1 ohm for a maximum output current of 500 mA.
For accurate current regulation, the sensing resistor should be a 0.5 - 1.0 W precision resistor, i. e. less than 1%
tolerance and low temperature coefficient.
VCC
+5 V
V MM
+
0.1 µF
0.1 µF
12
V
9
4
V
CC
19
V
MM1
MM2
Phase 1
10
Dis1
7
V R1
MA1
3
MB1
1
NJM3773
14
MA2
Phase 2
13
Dis 2
16
MB2
V R2
RC
11
GND
C1
5, 6,
17, 18
+5 V 12 kΩ
E1
2
8
10 µF
C2
20
22
STEPPER
MOTOR
E2
15
21
Pin numbers refer
to DIP package.
4 700 pF
RS
RS
0.47 Ω
0.47 Ω
GND (V MM )
GND (VCC )
Figure 6. Typical stepper motor driver application with NJM3773.
+5 V
V MM
V CC
+
+
4.7 µF
0.1 µF
0.1 µF
12
V
Microcontroller
9
10
7
D/A
13
16
D/A
82 kΩ
V R1
1000
pF
1000
pF
MA1
3
MB1
1
NJM3773
MA2
Dis 2
V R2
RC GND
2 700 pF
5, 6,
17, 18
MB2
C1
E1
2
8
C2
E2
15
21
1 kΩ
1 kΩ
820 pF
820 pF
RS
0.68 Ω
GND (VCC )
MM2
Phase 2
20 kΩ
10 kΩ
V
MM1
Dis1
11
10 kΩ
V
CC
10 µF
19
Phase 1
82 kΩ
14
4
RS
20
22
STEPPER
MOTOR
Pin numbers refer
to DIP package.
0.68 Ω
GND (V MM )
Figure 7. Microstepping system where a microcontroller including DACs provides
analog current control voltages as well as digital signals to the NJM3773.
NJM3773
Current sense filtering
At turn-on a current spike occurs, due to the recovery of the recirculation diodes and the capacitance of the motor
winding. To prevent this spike from reseting the flip-flops through the current sensing comparators, the clock
oscillator generates a blanking pulse at turn-on. The blanking pulse disables the comparators for a short time.
Thereby any voltage transient across the sensing resistor will be ignored during the blanking time.
Choose the blanking pulse time to be longer than the duration of the switching transients by selecting a proper CT
value. The time is calculated as:
tb = 210 • CT [s]
As the CT value may vary from approximately 2 200 pF to 33 000 pF, a blanking time ranging from 0.5 µs to 7 µs is
possible. Nominal value is 4 700 pF, which gives a blanking time of 1.0 µs.
As the filtering action introduces a small delay, the peak value across the sensing resistor, and hence the peak
motor current, will reach a slightly higher level than what is defined by the reference voltage. The filtering delay
also limits the minimum possible output current. As the output will be on for a short time each cycle, equal to the
digital filtering blanking time plus additional internal delays, an amount of current will flow through the winding.
Typically this current is 1-10 % of the maximum output current set by RS.
Sometimes it may be necessary to include an external in the feed back loop, the filtering may be done by adding
an external low pass filter in series with the comparator C input. In this case the digital blanking time should be as
short as possible. The recommended filter component values are 1 kohm and 820 pF.
To create an absolute zero current, the Dis input should be HIGH.
Switching frequency
The frequency of the clock oscillator is set by the timing components RT and CT at the RC-pin. As CT sets the digital
filter blanking time, the clock oscillator frequency is adjusted by RT. The value of RT is limited to 2 - 20 kohm. The
frequency is approximately calculated as:
fs = 1 / ( 0.77 • RT • CT)
Nominal component values of 12 kohm and 4 700 pF results in a clock frequency of 23.0 kHz. A lower frequency
will result in higher current ripple, but may improve low level linearity. A higher clock frequency reduces current
ripple, but increases the switching losses in the IC and possibly the iron losses in the motor.
Phase inputs
A logic HIGH on a Phase input gives a current flowing from pin MA into pin 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.
Dis (Disable) inputs
A logic HIGH on the Dis inputs will turn off all four transistors of the output H-bridge, which results in a rapidly
decreasing output current to zero.
Phase 1
Dis 1
Phase 2
Thermal resistance [°C/W]
80
Dis 2
22-pin
DIP
70
V R1
140%
100%
60
V R2
140%
100%
50
I MA1
140%
40
24-pin
EMP
100%
–100%
30
–140%
I MA2
140%
100%
20
5
10
15
20
25
30
35
PCB copper foil area [cm 2 ]
PLCC package
DIP package
Figure 8. Typical thermal resistance vs. PC
Board copper area and suggested layout
28-pin
PLCC
–100%
–140%
Full step mode
Half step mode
Figure 9. Stepping modes
Modified half step mode
NJM3773
VR (Reference) inputs
The comparator inputs of NJM3773 (VR and C) are high impedance, low current inputs (typically -0.2 µA). This
gives a great deal of flexibility in selecting a suitable voltage divider network to interface to different types of Digitalto-Analog converters. Unbuffered DACs are preferably interfaced by a high resistive divider network ( typ. 100
kohm), while for buffered DACs a low resistive network (typ. 5 kohm) is recommended. A filter capacitor in conjunction with the resistor network will improve noise rejection. A typical filter time constant is 10 µs. See figure 7. In
basic full and half-stepping applications, the reference voltage is easily divided from the VCC supply voltage.
Interference
Due to the switching operation of NJM3773, noise and transients are generated and coupled into adjacent circuitry.
To reduce potential interference there are a few basic rules to follow:
• Use separate ground leads for power ground (the ground connection of RS), the ground leads of NJM3773, and
the ground of external analog and digital circuitry. The grounds should be connected together close to the GND
pins of NJM3773.
• Decouple the supply voltages close to the NJM3773 circuit. Use a ceramic capacitor in parallel with an electrolytic type for both VCC and VMM Route the power supply lines close together.
• Do not place sensitive circuits close to the driver. Avoid physical current loops, and place the driver close to both
the motor and the power supply connector. The motor leads could preferably be twisted or shielded.
Motor selection
The NJM3773 is designed for two-phase bipolar stepper motors, i.e. motors that have only one winding per phase.
The chopping principle of the NJM3773 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 NJM3773 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 in 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 maximum current.
Heat sinking
NJM3773 is a power IC, packaged in a power DIP, EMP or PLCC package. The ground leads of the package (the
batwing) are thermally connected to the chip. External heatsinking is achieved by soldering the ground leads onto a
copper ground plane on the PCB.
Maximum continuous output current is heavily dependent on the heatsinking and ambient temperature. Consult
figures 8, 10 and 11 to determine the necessary heatsink, or to find the maximum output current under varying
conditions.
A copper area of 20 cm2 (approx. 1.8” x 1.8”), copper foil thickness 35 µm on a 1.6 mm epoxy PCB, permits the
circuit to operate at 2 x 450 mA output current, at ambient temperatures up to 85°C.
Thermal shutdown
The circuit is equipped with a thermal shutdown function that turns the outputs off at a chip (junction) temperature
above 160°C. Normal operation is resumed when the temperature has decreased.
Programming
Figure 9 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.
NJM3773
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. The NJM3773 is designed to
handle about 1.4 times higher current in one channel on mode, for example 2 x 500 mA in the full-step position,
and 1 x 700 mA in the half-step position.
■ TYPICAL CHARACTERISTICS
PD (W)
VCE Sat (V)
Maximum allowable power dissipation [W]
6
1.2
5
3.0
nt
te
3
1.0
Tw
o
c
ha
e
nn
ls
on
ra
tu
re
2
l on
nne
1.0
0.8
0.6
0.4
0
-25
O
0
pe
1
ha
ne c
0
m
ture
pera
tem
2.0
bie
pin
ing
Batw
Am
4
0.2
0
25
50
75
100
125
150
Temperature [°C]
0.20
0.40
0.60
0.80
PLCC package
DIP package
I M (A)
Figure 10. Typical power dissipation
vs. motor current.Ta = 25°C
0
All ground pins soldered onto a
20 cm2 PCB copper area with
free air convection.
0
VCE Sat (V)
1.2
1.0
1.0
1.0
0.8
0.8
0.8
0.6
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
0
0
0.40
0.60
0.80
I M (A)
Figure 13. Typical lower diode
voltage drop vs. recirculating current
0.80
Vd, ud (V)
1.2
0.20
0.60
I M (A)
1.2
0
0.40
Figure 11. Maximum allowable power Figure 12. Typical lower transistor
saturation voltage vs. output current
dissipation
Vd, ld (V)
0
0.20
0
0.20
0.40
0.60
0.80
I M (A)
Figure 14. Typical upper transistor
saturation voltage vs. output current
0
0.20
0.40
0.60
0.80
I M (A)
Figure 15. Typical upper diode
voltage 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.
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