NJM37770
STEPPER MOTOR DRIVER
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GENERAL DESCRIPTION
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 pin-
compatible with the NJM37717and 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.
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PACKAGE OUTLINE
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EATURES
• Half-step and full-step operation
• Switched mode bipolar constant current drive
• Wide range of current control 5 -1500 mA
• Wide voltage range 10 - 60 V
• Thermal overload protection
• Packages DIP16 (Batwing)
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BLOCK DIAGRAM
Figure 1. Block diagram
NJM37770
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PIN CONFIGURATIONS
Figure 2. Pin configurations
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PIN DESCRIPTION
DIP
Symbol
Description
1
2
3,14
4,5,
12,13
6
7
M
B
T
V
MM
GND
V
CC
I
1
8
9
Phase
I
0
10
11
15
16
C
V
R
M
A
E
Motor output B, Motor current flows from M
A
to M
B
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 M
A
and M
B
outputs.
Motor current flows from M
A
to M
B
when the phase input is high.
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%.
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 M
A
to M
B
when Phase is high.
Common emitter. Connect the Sense resistor between this pin and ground.
NJM37770
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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 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 M
A
to M
B
and low input from terminal M
B
to M
A
. 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.
Figure 3. Output stage with current paths
for fast and slow current decay.
Figure 4. Motor current (I
M
),
Vertical : 200 mA/div,
Horizontal: 1 ms/div,
expanded part 100 µs/div.
NJM37770
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
High level
Low level
Zero current
100%
20%
0%
Medium level 60%
I
0
L
L
I
1
L
H
H L
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 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, 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 triggered 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, connected in an H-bridge. Note that the upper recircula-
tion 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 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 (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 appropri-
ate 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 I
1
and I
0
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.
NJM37770
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ABSOLUTE MAXIMUM RATINGS
Parameter
Pin no. [DIP 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
T
j
T
s
-40
-55
+150
+150
°C
°C
1, 15
7,8,9
10,11
I
M
I
I
I
A
-1500
-10
-10
+1500
-
-
mA
mA
mA
6
3, 14
7,8,9
10
11
V
CC
V
MM
V
I
V
C
V
R
0
0
-0.3
-0.3
-0.3
7
60
6
V
CC
15
V
V
V
V
V
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RECOMMENDED OPERATING CONDITIONS (Ta=25
°C
)
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
V
CC
V
MM
I
M
T
J
t
r
t
f
4.75
10
-1300
-20
-
-
5
-
-
-
-
-
5.25
55
+1300
+125
2
2
V
V
mA
°C
µs
µs
Figure 5. Definition of symbols
Figure 6. Definition of terms
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