NJM3776D2 データシートの表示（PDF） - Japan Radio Corporation

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NJM3776D2

DUAL CONTROLLER FOR HIGH-CURRENT STEPPER MOTOR

Japan Radio Corporation  

NJM3776

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 7 shows the different input and output sequences for full-step, half-step and modified half-step 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.

Half-step mode.

In the half-step mode, the current in one winding is brought to zero before a complete current reversal is made. The

motor will then have taken two half steps equalling one full step in rotary movement. The cycle is repeated, but on

the other phase. A total of eight states are sequenced until the initial state is reached again.

Half-step mode can overcome potential resonance problems. Resonances appear as a sudden loss of torque at

one or more distinct stepping rates and must be avoided so as not to loose control of the motor´s shaft position.

One disadvantage with the half-step mode is the reduced torque in the half step positions, in which current flows

through one winding only. The torque in this position is approximately 70 % of the full step position torque.

Modified half-step mode

.The torque variations in half step mode will be elimi-nated if the current is increased about 1.4 times in the half-

step position. A constant torque will further reduce resonances and mechanical noise, resulting in better perfor-

mance, life expectancy and reliability of the mechanical system.

Modifying the current levels must be done by bringing the reference voltage up (or down) from its nominal value

correspondingly. This can be done by using DACs or simple resistor divider networks.

See SMD and application handbook for more information on implementing modified half step.

s TYPICAL CHARACTERISTICS

VCE Sat (V)

0.6

0.4

0.2

0

0

0.20

0.40

I M (A)

Figure 9. Typical lower transistor

saturation voltage vs. output current

VCE Sat (V)

1.2

1.0

0.8

0.6

0.4

0.2

0

0

0.20

0.40

I M (A)

Figure 10. Typical upper transistor

saturation voltage vs. output current

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.

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