NJM3517E2 データシートの表示（PDF） - Japan Radio Corporation

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NJM3517E2

STEPPER MOTOR CONTROLLER / DRIVER

Japan Radio Corporation  

NJM3517

7. To change actual motor rotation direction, exchange motor connections at PA1 and PA2 (or PB1 and PB2).

8. 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 the 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.

9. Ramping. Every drive system has inertia which must be considered in the drive scheme. The rotor and load

inertia plays a big role at higher speeds. Unlike the DC motor, the stepper motor is a synchronous motor and

does not change speed due to load variations. Examination of typical stepper motors’ torque versus speed

curves indicates a sharp torque drop-off for the start-stop without error curve. The reason for this is that the

torque requirements increase by the cube of the speed change. As it can be seen, for good motor perfor-

mance, controlled acceleration and deceleration should be considered.

s COMMON FAULT CONDITIONS

• VMM supply not connected, or VMM supply not connected through diodes.

• The inhibit input not pulled low or floating. Inhibit is active high.

• A bipolar motor without a center tap is used. Exchange motor for unipolar version. Connect according to figure 3.

• External transistors connected without proper base-current supply resistor.

• Insufficient filtering capacitors used.

• Current restrictions exceeded.

• LA and LB used for continuous output at high currents. Use the RC network to set a proper duty cycle according

to specifications, see figures 19 through 24.

• A common ground wire is used for all three power supplies. If possible, use separate ground leads for each

supply to minimize power interference.

s DRIVE CIRCUITS

If high performance is to be achieved from a stepper motor, the phase must be energized rapidly when turned on

and also de-energize rapidly when turned off. In other words, the phase current must increase/decrease rapidly at

phase shift.

s PHASE TURN-OFF CONSIDERATIONS

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

suppressed. Different turn-off circuits

are used; e. g. :

Diode turn-off circuit (figure 12)

— Slow current decay

— Energy lost mainly in winding resistance

— Potential cooling problems.

Resistance T O C (figure 13)

— Somewhat faster current decay

— Energy lost mainly in R-Ext

— Potential cooling problems

Zener diode T O C (figure 14)

Relatively high VZ gives:

— Relatively fast current decay

— Energy lost mainly in VZ

— Potential cooling problems

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