2-Phase Stepper Motor Bipolar Driver ICs (2-Phase/1-2 Phase Excitation)
A3952SB/SLB/SW
(F) Application circuit (Bipolar stepper motor drive)
Fig. 4 Example of stepper motor drive
V
BB
+5V
12
+
47
µ
F
1
11
2
10
MODE
1
ENABLE
1
PHASE
1
0.5
V
BB
3
0.5
V
REF2
9
4
8
5
LOGIC
V
CC
6
7
V
CC
LOGIC
7
6
V
REF1
PHASE
2
C
T=
820pF/1200pF
R
T=
17k
Ω/
25k
5
8
ENABLE
2
MODE
2
4
9
10
V
BB
2
3
11
12
1
R
T=
17k
Ω/
25k
C
T=
820pF/1200pF
t
off
R
T•
C
T
(Chopping off-time setting)
R
T =
12k~100kΩ
C
T =
820~1500pF (When using slow current-decay mode only)
1200~1500pF (When using fast current-decay mode only)
(G)DC Motor Applications
In closed-loop systems, the speed of a dc motor can be con-
trolled by PWM of the PHASE or ENABLE inputs, or by varying
the REF input voltage (V
REF
). In digital systems (microproces-
sor controlled), PWM of the PHASE or ENABLE input is used
typically thus avoiding the need to generate a variable analog
voltage reference. In this case, a dc voltage on the REF input is
used typically to limit the maximum load current.
In dc servo applications that require accurate positioning at low
or zero speed, PWM of the PHASE input is selected typically.
This simplifies the servo-control loop because the transfer func-
tion between the duty cycle on the PHASE input and the aver-
age voltage applied to the motor is more linear than in the case
of ENABLE PWM control (which produces a discontinuous cur-
rent at low-current levels).
With bidirectional dc servo motors, the PHASE terminal can be
used for mechanical direction control. Similar to when braking
the motor dynamically, abrupt changes in the direction of a ro-
tating motor produce a currrent generated by the back EMF.
The current generated will depend on the mode of operation. If
the internal current-control circuitry is not being used, then the
maximum load current generated can be approximated by
I
LOAD
(V
BEMF
+ V
BB
)
R
LOAD
I
LOAD
regulate to a value given by
V
REF
(10
R
S
)
CAUTION:
In fast-decay mode, when the direction of the motor
is changed abruptly, the kinetic energy stored in the motor and
load inertia will be converted into current that charges the V
BB
supply bulk capacitance (power supply output and decoupling
capacitance). Care must be taken to ensure the capacitance is
sufficient to absorb the energy without exceeding the voltage
rating of any devices connected to the motor supply.
See also, the sections on brake operation under “Functional
Description,” above.
where V
BEMF
is proportional to the motor’s speed. If the internal
slow-decay current-control circuitry is used, then the maximum
load current generated can be approximated by I
LOAD
=V
BEMF
/
R
LOAD
. For both cases, care must be taken to ensure the maxi-
mum ratings of the device are not exceeded. If the internal fast-
decay current-control circuitry is used, then the load current will
76
A3952SB/SLB/SW
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