NJM3771

NJM3771
DUAL STEPPER MOTOR DRIVER
■ GENERAL DESCRIPTION
The NJM3771 is a stepper motor driver, which circuit is
especially developed for use in microstepping applications
in conjunction with the matching dual DAC (Digital-to-Analog Converter) NJU39610.
The NJM3771 contains a clock oscillator, which is
common for both driver channels; a set of comparators and
flip-flops imple menting the switching control; and two
H-bridges with internal recirculation diodes. Voltage supply
requirements are +5 V for logic and +10 to +45 V for the
motor. Maximum output current is 650 mA per channel.
■ PACKAGE OUTLINE
■ FEATURES
● Dual chopper driver
● 650mA output current per channel
● Selectable slow / fast current decay for improved highspeed microstepping
● Specially matched to Dual DAC NJU39610
● Packages
DIP22-D2 / PLCC28-M2
SOP24 JEDEC 300 mil (Batwing)
NJM3771D2
( DIP22 )
NJM3771E3
( SOP24 )
NJM3771FM2
( PLCC28 )
■ BLOCK DIAGRAM
Figure 1. Block diagram
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NJM3771
■ PIN CONFIGURATION
Figure 2. Pin configurations
■ PIN DESCRIPTION
Refer to Figure 2.
SOP
DIP
PLCC
Symbol
2
3
4
Description
1
8
MB1
Motor output B, channel 1. Motor current flows from MA1 to MB1 when Phase1 is HIGH.
2
10
E1
Common emitter, channel 1. This pin connects to a sensing resistor to ground.
3
11
VMM1
Motor supply voltage, channel 1, 10 to 40 V. VMM1 and VMM2 should be connected together.
5
4
12
MA1
Motor output A, channel 1. Motor current flows from MA1 to MB1 when Phase1 is HIGH.
6, 7,
18,19
5, 6,
17, 18
1-3, 9,
13-17, 28
GND
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.
8
7
18
Phase1
Controls the direction of motor current at outputs MA1 and MB1. Motor current flows from MA1
to MB1 when Phase1 is HIGH.
9
8
19
CD1
Current decay control, channel 1. A logic HIGH on this input results in slow current decay, a
LOW results in fast current decay, see “Functional Description”
10
9
20
VR1
Reference voltage, channel 1. Controls the threshold voltage for the comparator and hence
the output current. input resistance is typically 2.5kohms, ±20%.
11
10
21
C1
Comparator input channel 1. This input senses the instantaneous voltage across the sensing
resistor, filtered by an RC network. The threshold voltage for the comparator is (0.450 / 2.5)･
VR1, i.e. 450mV at VR1=2.5V.
12
11
22
VCC
Logic voltage supply, nominally +5 V.
13
12
23
RC
Clock oscillator RC pin. Connect a 15 kohm resistor to VCC and a 3 300 pF capacitor to
ground to obtain the nominal switching frequency of 26.5 kHz.
14
13
24
C2
Comparator input channel 2. This input senses the instantaneous voltage across the sensing
resistor, filtered by an RC network.The threshold voltage for the comparator is (0.450 / 2.5)･
VR1, i.e. 450mV at VR1=2.5V.
15
14
25
VR2
Reference voltage, channel 2. Controls the threshold voltage for the comparator and hence
the output current. input resistance is typically 2.5kohms, ±20%.
16
15
26
CD2
Current decay control, channel 1. A logic HIGH on this input results in slow current decay, a
LOW results in fast current decay, see “Functional Description”
17
16
27
Phase2
Controls the direction of motor current at outputs MA2 and MB2. Motor current flows from MA2
to MB2 when Phase2 is HIGH.
20
19
4
MA2
Motor output A, channel 2. Motor current flows from MA2 to MB2 when Phase2 is HIGH.
21
20
5
VMM2
Motor supply voltage, channel 2, +10 to +40 V. VMM1 and VMM2 should be connected
together.
22
21
6
E2
Common emitter, channel 2. This pin connects to a sensing resistor to ground.
23
22
7
MB2
Motor output B, channel 2. Motor current flows from MA2 to MB2 when Phase2 is HIGH.
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Ver.2011-12-08
NJM3771
■ FUNCTIONAL DESCRIPTION
Each channel of the NJM3771 consists of the following sections: an H-bridge output stage, capable of driving up to 650
mA continuous motor current (or 500 mA, both channels driven), a logic section that controls the output transistors, an
S-R flip-flop, and two comparators. The oscillator is common to both channels.
Constant current control is achieved by switching the current to the windings. This is done by sensing the (peak)
voltage across a current-sensing resistor, RS, effectively connected in series with the motor winding, and feeding that
voltage back to a comparator. When the motor current reaches a threshold level, determined by the voltage at the
reference input, VR, the comparator resets the flip-flop, which turns off the output transistors. The current decreases until
the clock oscillator triggers the flip-flop, which turns on the output transistors again, and the cycle is repeated.
The current-decay rate during the turn-off portion of the switching cycle, can be selected fast or slow by the CD input.
In slow current-decay mode, only one of the lower transistors in the H-bridge (those closest to the negative supply) is
switched on and off, while one of the upper transistors is held constantly on. During turn-off, the current recirculates
through the upper transistor (which one depends on current direction) and the corresponding freewheeling diode
connected to VMM, see figure 3.
In fast current decay mode, both the upper and lower transistors are switched. During the off-time, the freewheeling
current is opposed by the supply voltage, causing a rapid discharge of energy in the winding.
Fast current decay may be required in half- and microstepping applications when rapid changes of motor current are
necessary. Slow current decay, however, gives less current ripple, and should always be selected, if possible, to minimize
core losses and switching noise.
Figure 3. Output stage with current paths
during turn -on, turn-off and phase shift
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NJM3771
■ ABSOLUTE MAXIMUM RATINGS
Parameter
Pin no. (DIP)
Symbol
Min
Max
Unit
Voltage
Logic supply
11
VCC
0
7
V
Motor supply
3, 20
VMM
0
45
V
Logic inputs
V
7, 8, 15, 16
VI
-0.3
6
Comparator inputs
10, 13
VC
-0.3
VCC
V
Reference inputs
9, 14
VR
-0.3
7.5
V
Motor output current
1, 4, 19, 22
IM
-700
+700
mA
Logic inputs
7, 8, 15, 16
II
-10
-
mA
10, 13
IA
-10
-
mA
12
IRC
-
5
mA
Operating junction temperature
TJ
-40
+150
°C
Storage temperature**
Tstg
-55
+150
°C
Symbol
Min
Typ
Max
Unit
Logic supply voltage
VCC
4.75
5
5.25
V
Motor supply voltage
VMM
10
-
40
V
Motor output current ***
IM
-650
-
650
mA
Junction temperature ****
Tj
-20
-
+125
°C
Rise time logic inputs
tr
-
-
2
µs
Fall time logic inputs
tf
-
-
2
µs
RT
2
15
20
kohm
Current
Analog inputs
Oscillator charging current
Temperature
** Circuit only. The packaging can handle max 60°C
■ RECOMMENDED OPERATING CONDITIONS
Parameter
Oscillator timing resistor
*** In microstepping mode, “sine/cosine” drive where I1 = 650 • cos(q) and I2 = 650 • sin(q) mA, otherwise 500 mA/channel both channels fully
on.
****See operating temperature chapter.
Figure 4. Definitions of symbols
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Figure 5. Definition of terms
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NJM3771
■ ELECTRICAL CHARACTERISTICS
Electrical characteristics over recommended operating conditions, unless otherwise noted. -20°C ≤ Tj ≤ +125°C
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
-
38
50
mA
VMM = 40 V, IM1= 450 mA, IM2= 0 mA.
Notes 2, 3.
1.4
1.6
W
VMM = 40 V, IM1 = IM2 = 318 mA.
Notes 2, 3.
1.6
1.8
W
1.0
1.5
µs
General
Supply current
ICC
Total power dissipation
PD
Turn-off delay
td
Ta = +25°C, dVC/dt ≥50 mV/µs.Note 3.
-
Logic Inputs
Logic HIGH input voltage
VIH
2.0
-
-
V
Logic LOW input voltage
VIL
-
-
0.6
V
Logic HIGH input current
IIH
VI = 2.4 V
-
-
20
µA
Logic LOW input current
IIL
VI = 0.4 V
-0.4
-
-
mA
RR
Ta = +25°C
-
5
-
kohm
IR
Ta = +25°C, VR = 2.5 V.
Reference Inputs
Input resistance
Input current
Turn-off voltage
VTO
0.5
1.0
mA
20
29
38
mV
430
450
470
mV
-
1
-
mV
-10
-
1
µA
Comparator Inputs
Threshold voltage
| VCH1 - VCH2 | mismatch
VCH
VCH,diff
Input current
RC = 1 kohms, VR = 2.5 V
RC = 1 kohms
IC
Motor Outputs
Lower transistor saturation voltage
IM = 500 mA
-
1.00
1.20
V
Lower transistor leakage current
VMM = 41 V, VE = VR = 0 V, VC = VCC
-
-
300
µA
Lower diode forward voltage drop
IM = 500 mA
-
1.10
1.25
V
Upper transistor saturation voltage
IM = 500 mA
1.20
1.35
V
-
Upper transistor leakage current
VMM = 41 V, VE = VR = 0 V, VC = VCC
-
-
300
µA
Upper diode forward voltage drop
IM = 500 mA
-
1.00
1.25
V
25.0
26.5
28.0
kHz
Min
Typ
Max
Unit
°C/W
Chopper Oscillator
Chopping frequency
fS
CT = 3300 pF, RT = 15 kohms
■ THERMAL CHARACTERISTICS
Parameter
Thermal resistance
Symbol
RthJ-GND
RthJ-A
RthJ-GND
RthJ-A
RthJ-GND
RthJ-A
Conditions
DIP package.
-
11
-
DIP package. Note 2.
-
40
-
°C/W
PLCC package.
-
9
-
°C/W
PLCC package. Note 2.
-
35
-
°C/W
SOP package.
-
13
-
°C/W
SOP package. Note 2.
-
42
-
°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.
3. Not covered by final test program.
4. Switching duty cycle D = 30%, fS = 26.5 kHz
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NJM3771
■ APPLICATIONS INFORMATION
Current control
The output current to the motor winding is mainly determined by the voltage at the reference input and the value of the
sensing resistor, RS.
Chopping frequency, winding inductance, and supply voltage will affect the current level, but to much less extent. Fast
current decay setting will produce somewhat lower (average) current than slow current decay. The peak current through
the sensing resistor (and motor winding) can be expressed as:
IM,peak = 0.18 • (VR / RS) [A]
i.e., with a recommended value of 1 ohm for the sensing resistor, RS, a 2.5 V reference voltage will produce an output
current of approximately 450 mA. To improve noise immunity on the VR input, the control range may be increased to 5
volts if RS is correspondingly changed to 2 ohms.
Figure 6. Typical stepper motor application with NJM3771
Figure 7. Microstepping system with NJU39610 and NJM3771
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NJM3771
External components
The voltage across the sensing resistor is fed back to the comparator via a low-pass filter section, to prevent erroneous
switching due to switching transients. The recommended filter component values, 1 kohm and 820 pF, are suitable for a
wide range of motors and operational conditions.
Since the low-pass filtering action introduces a small delay of the signal to the comparator, peak voltage across the
sensing resistor, and hence the peak motor current, will reach a slightly higher level than the threshold, VC, set by the
reference voltage
(VC = 450 mV @VR = 2.5 V).
The time constant of the low-pass filter may therefore be reduced to minimize the delay and optimize low-current
performance, especially if a low (12 V) supply voltage is used. Increasing the time constant may result in unstable
switching.
The frequency of the clock oscillator is set by the RT-CT combination at pin RC. The recommended values give a
nominal frequency of 26.5 kHz. A lower frequency will result in higher current ripple and may cause audible noise from
the motor, while increasing the frequency results in higher switching losses and possibly increased iron losses in the
motor.
The sensing resistor, RS, should be selected for maximum motor current. The relationship between peak motor current,
reference voltage and the value of RS is described under “Current control” above. Be sure not to exceed the maximum
output current which is 650 mA per channel (or 500 mA per channel, both channels fully on, see “Recommended
Operating Conditions”).
Motor selection
The NJM3771 is designed for bipolar motors, i.e., motors that have only one winding per phase. A unipolar motor,
having windings with a center tap, can also be used, see figure 8.
The chopping principle in the NJM3771 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%. To avoid this, it is necessary to choose a motor with a low winding resistance. Low winding
resistance means less inductance and will therefore enable higher stepping rates, however it also means less torque
capability. A compromise has to be made.
Choose a motor with the lowest possible winding resistance 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.
Since the NJM3771 produces a regulated, constant output current it is not necessary to use a motor that is rated at the
same voltage as the actual supply voltage. Only rated current needs to be considered. Typical motors to be used
together with the NJM3771 have voltage ratings of 5 to 12 V, while the supply voltage usually ranges from 24 to 40 V.
Figure 8. Connection of unipolar motors
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NJM3771
General
Phase inputs
A logic HIGH on a Phase input gives positive current flowing out from MA into MB. A logic LOW gives a current in the
opposite direction.
Slow/fast current decay
A logic HIGH on the CD input gives slow current decay, a logic LOW gives fast current decay.
Heat sinking
Soldering the four center pins onto a free PCB copper area of 20 cm2 (approx. 1.8" x 1.8", copper foil thickness = 35
µm) permits the circuit to operate with a maximum of 320 mA output current, both channels driving, at ambient
temperatures up to +70°C. Consult figures 9 and 14 in order to determine the necessary copper area for heat sinking if
higher currents are required.
Thermal shutdown
The circuit is equipped with a thermal shutdown function that reduces the output current at chip temperatures above
+160°C.
Figure 9. Thermal Resistance vs. PC Board copper area and suggested layout
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NJM3771
■ TYPICAL CHARACTERISTICS
Figure 10. Typical upper diode
voltage drop vs. recirculating current
Figure 11. Typical source saturation
voltage vs. output current
Figure 12. Typical lower diode
voltage drop vs. recirculating current
Figure 13 Typical sink saturation
voltage vs. output current
Figure 14. Power dissipation vs. motor current,
both channels driven, Ta = 25°C
[CAUTION]
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.
Ver.2011-12-08
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