NJM3773 데이터 시트보기 (PDF) - Japan Radio Corporation

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NJM3773

DUAL STEPPER MOTOR DRIVER

Japan Radio Corporation  

NJM3773

VR (Reference) inputs

The comparator inputs of NJM3773

(V

R

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 Digital-

to-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 con-

junction 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 V supply voltage.

CC

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 electro-

lytic 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.

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