NJM3773
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 halfstep
position. A constant torque will further reduce resonances and mechanical noise, resulting in better performance,
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. The NJM3773 is designed to
handle about 1.4 times higher current in one channel on mode, for example 2 x 500 mA in the full-step position,
and 1 x 700 mA in the half-step position.
s
TYPICAL CHARACTERISTICS
P
D
(W)
6
5
ture
pera
tem
pin
ing
Batw
Am
Maximum allowable power dissipation [W]
V
CE Sat
(V)
3.0
1.2
bie
4
nt
1.0
0.8
0.6
0.4
0.2
te
m
pe
2.0
ls
ne
on
3
ra
tu
re
2
1.0
Tw
o
ch
an
1
0
0
One
nn
cha
el o
n
0
-25
0
25
50
75
100
125
150
Temperature [°C]
0.40
0.60
0.80
0.20
0
0
0.20
0.40
0.60
0.80
I
M
(A)
PLCC package
DIP package
All ground pins soldered onto a
20 cm
2
PCB copper area with
free air convection.
I
M
(A)
Figure 10. Typical power dissipation
vs. motor current.T
a
= 25°C
V
d, ld
(V)
Figure 11. Maximum allowable power Figure 12. Typical lower transistor
saturation voltage vs. output current
dissipation
V
CE Sat
(V)
V
d, ud
(V)
1.2
1.0
0.8
0.6
0.4
0.2
1.2
1.0
0.8
0.6
0.4
0.2
0
1.2
1.0
0.8
0.6
0.4
0.2
0
0
0.20
0.40
0.60
0.80
0
0
0.20
0.40
0.60
0.80
0
0.20
0.40
0.60
0.80
I
M
(A)
I
M
(A)
I
M
(A)
Figure 13. Typical lower diode
voltage drop vs. recirculating current
Figure 14. Typical upper transistor
saturation voltage vs. output current
Figure 15. Typical upper diode
voltage drop vs. recirculating 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.
NJRC [ NEW JAPAN RADIO ]
