NJW4351 데이터 시트보기 (PDF) - Japan Radio Corporation

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NJW4351

Unipolar Stepper Motor Driver

Japan Radio Corporation  

NJW4351

PRECAUTIONS

1. Never disconnect the device or PC-board when power is supplied.

2. Remember that excessive voltages might be generated by motor, even though clamping diodes are used.

3. Choose a motor that is proportional to the current you need to establish desired torque. A high supply voltage

will gain better stepping performance. If the motor is not specified for the VMM voltage, a current limiting

resistor will be necessary to connect in series with center tap. This changes the L/R time constant.

4. Avoid VMM and VDD power supplies with serial diodes (without filter capacitor) and common ground with

VDD.

5. To change actual motor rotation direction, exchange motor connections at OUT1A and OUT1B (OUT2A and

OUT2B).

6. Half-stepping

In the half-step mode, the power input to the motor alternates between one or two phase windings. In

half-step mode, motor resonances are reduced. In a two-phase motor, the electrical phase shift between the

windings is 90 degrees. The torque developed is the vector sum of two windings energized. Therefore, when

only one winding is energized, which is the case in half-step mode for every second step, the torque of the

motor is reduced by approximately 30%. This causes a torque ripple.

7. Drive Circuits

High-performance stepper motor operation requires windings to be energized immediately at phase turn-on

and quickly turned off when not in use.

8. Phase Turn-off Considerations

When the winding current is turned off, induced high voltage spike will damage the drive circuits if not

properly suppressed. Refer to the turn-off circuits described in Figures 11 to 14.

The voltage potential at the phase output terminal may sometimes become negative (GND or below) due to

the configuration of the turn-off circuit or the kickback voltage generated in it. In this condition there is a danger

of a malfunction occurring in the logic circuit inside the device.

8.1. Precautions against high voltage using the Zener-diode turn-off circuit

Refer the Zener-diode turn-off circuit (see Fig.15). Zener-diode voltage value is Vz and the forward voltage of

the diodes connected in series with the Zener-diode is Vd, the voltage VP of the phase output (OUT1A,

OUT1B, OUT2A, OUT2B) terminal when the turn-off operation have occurred is expressed by the following

equation. VP = VMM – (Vz + Vd)

The higher voltage, Vz, used, the shorter is the turn-off time of the winding current, thus producing high

speed operation of the stepper motor. Note, however, that depending on the Zener voltage, VZ, the voltage

potential at the phase output terminal may become negative, so design the turn-off circuit as indicated below.

8.1.1. When VP is a positive voltage: VMM > VZ + Vd

The circuit configuration is that of Fig.15.

Set the Zener voltage. For example, if VMM is 12 V, VZ + Vd is no higher than12V.

8.1.2 When VP is a negative voltage: VMM < VZ + Vd

The circuit configuration is that of Fig.16. In order to prevent a malfunction due to a negative voltage, be sure

to insert diodes in series with the phase output terminals.

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