2-Phase Stepper Motor Unipolar Driver IC (2-Phase/1-2 Phase Excitation)
SLA7032M/SLA7033M
sDetermining
the Output Current
Fig. 1 shows the waveform of the output current (motor coil cur-
rent). The method of determining the peak value of the output
current (I
O
) based on this waveform is shown below.
(Parameters for determining the output current I
O
)
V
b
: Reference supply voltage
r
1
,r
2
: Voltage-divider resistors for the reference supply voltage
R
S
: Current sense resistor
(1) Normal rotation mode
I
O
is determined as follows when current flows at the maximum
level during motor rotation. (See Fig.2.)
I
O
≅
r
2
r
1
+r
2
•
Fig. 1 Waveform of coil current (Phase A excitation ON)
I
O
Phase A
0
Phase A
V
b
................................................................
(1)
R
S
Fig. 2 Normal mode
V
b
(5
V
)
r
1
3,(14)
r
2
9,(10)
R
S
(2) Power down mode
The circuit in Fig.3 (r
x
and T
r
) is added in order to decrease the
coil current. I
O
is then determined as follows.
I
OPD
≅
1+
1
r
1
(r
2
+r
X
)
r
2
•
r
X
1
1
r
1
V
b
R
s
•
I
OPD
−1
−
1
r
2
•
V
b
......................................................... (2)
R
S
Equation (2) can be modified to obtain equation to determine r
x
.
r
X
=
Fig. 3 Power down mode
V
b
(5
V
)
r
1
Fig. 4 and 5 show th e graphs of equations (1) and (2) respec-
tively.
3,(14)
9,(10)
r
X
Power down
signal
T
r
r
2
Fig. 4 Output current I
O
vs. Current sense resistor R
S
Fig. 5 Output current I
OPD
vs. Variable current sense resistor r
x
4
2.0
2
r
2
· V
b
I
O
=
r
1
+r
2
R
S
r
1
=510Ω
r
2
=100Ω
r
x
=∞
V
b
=5V
Output current I
OPD
(A)
Output current I
O
(A)
3
1.5
R
S
=0.5Ω
1
· V
b
r
1
(r
2+
r
X
)
R
S
1+
r
2 ·
r
X
r
1
=510Ω
r
2
=100Ω
V
b
=5V
I
OPD
=
1.0
R
S
=0.8Ω
R
S
=1Ω
1
0.5
0
0
1
2
3
4
00
200
400
600
800
1000 1200
Current sense resistor R
S
(Ω)
Variable current sense resistor r
X
(Ω)
32
SLA7032M/SLA7033M