5-Phase Stepper Motor Driver ICs (Pentagon Connection)
SI-7502
(SLA5011/SLA6503)
Application Notes
sDetermining
the Output Current I
O
(Control Current)
The main factors that determine the output current are current
sense resistor R
S
, supply voltage V
b
, and variable current resis-
tor R
X
.
(1) Normal mode
To operate a motor at the maximum current level, set R
X
to
infinity (open).
From Fig. A, when the maximum current ripple is designated
as I
OH
, its value will be,
R
S
V
RSH
Fig. A
I
OH
O
Waveform of output current
Fig. B Output current vs. Current sense resistor
(A)
3
I
OH(max)
=
0.212×V
b
−0.01
Rs
0.169×V
b
−0.03
Rs
V
RSH
can be calculated as follows:
V
RSH
=0.19×V
b
−0.03
(center value) ............................... (2)
From equations (1) and (2), the output current I
OH
can be
calculated as follows:
I
OH
=
1
R
S
(0.19×V
b
×-0.03)
Output current I
OH
I
OH
=
...................................................................... (1)
2
I
OH(min)
=
1
I
OH(max)
(V
b
=5V)
0.5
I
OH(min)
(V
b
=5V)
0.2
1
2
3
4
5
(Ω)
The relationship between I
OH
and R
S
is shown in Fig. B.
(2) Power down mode
When an external resistor R
X
is connected, V
RSH
changes as
shown in Fig. C even when R
S
is retained. Obtain a power
down output current I
OHPD
from Fig. C and equation (1).
Sense voltage V
RSH
Sense resistor Rs
Fig. C Sense voltage vs. Variable current resistor
(V)
1.0
V
RSH (max)
=
7.2×R
X
×V
b
−0.01
152.6+33.8×R
X
6.1×R
X
×V
b
−0.03
152.6+33.8×R
X
)
ax
(m
sRelation
between Output Current I
O
(Control
Current) and Motor Winding Current I
OM
The SI-7502 uses the total current control system; therefore,
the output current I
O
is different from the motor winding current.
In a general pentagonal driving system, the current flows as
shown in Figure D. The relation between I
O
and I
OM
is as follows:
I
O
=4×I
OM
With some driving systems, the relation can also be as follows:
I
O
=2×I
OM
0.8
V
RSH (min)
=
(V
b
=
5V
)
)
0.6
V
SH
R
V
H
RS
(m
in
V)
=5
b
(V
0.4
0.2
0.5
1
2
5
10
20 (KΩ)
Variable current resistor Rx
Fig. D Coil current flow at pentagonal driving
I
OM
I
OM
I
OM
2×I
OM
V
CC
I
OM
2×I
OM
to SI-7502
Sense resistor Rs
4×I
OM
SI-7502
(SLA5011/SLA6503)
107
SANKEN [ SANKEN ELECTRIC ]
