2-Phase Stepper Motor Bipolar Driver ICs (2-Phase/1-2 Phase Excitation)
A3952SB/SLB/SW
device. C
T
then should be increased until the measured value
of t
on (min)
is equal to t
on (min)
max)=3.0
µ
s as specified in the electri-
cal characteristics table. When the new value of C
T
has been
set, the value of R
T
should be decreased so the value for
t
off
=R
T
•
C
T
(with the artificially increased value of C
T
) is equal to
105% of the nominal design value. The worst-case load current
regulation then can be measured in the system under operating
conditions.
In applications utilizing both fast-and slow-decay internal PWM
modes, the performance of the slow-decay current regulation
should be evaluated per the above procedure and a t
on (min)
max
of 3.8
µ
s. This corresponds to a C
T
value of 1200pF, which is
required to ensure sufficient blanking during fast-decay internal
PWM.
blanking signal (t
1
) and the period of the PWM cycle (t
2
). The
value of t
1
should be a minimum of 1.5
µ
s in slow-decay mode
and 2
µ
s in fast-decay mode. When used in this configuration,
the R
T
and C
T
components should be omitted. The PHASE and
ENABLE inputs should not be PWMed with this circuit configu-
ration due to the absence of a blanking function synchronous
with their transitions.
Fig. 3 Synchronous Fixed-Frequency Control Circuit
V
CC
t
2
100 kΩ
20 kΩ
RC
1
1N4001
2N2222
(F) LOAD CURRENT REGULATION WITH EXTERNAL PWM
OF THE PHASE AND ENABLE INPUTS
The PHASE and ENABLE inputs can be pulse-width modulated
to regulate load current. Typical propagation delays from the
PHASE and ENABLE inputs to transitions of the power outputs
are specified in the electrical characteristics table. If the internal
PWM current control is used, then the comparator blanking func-
tion is active during phase and enable transitions. This elimi-
nates false tripping of the over-current comparator caused by
switching transients (see “RC Blanking” above).
(1) ENABLE Pulse-Width Modulation
With the MODE input low, toggling the ENABLE input turns ON
and OFF the selected source and sink drivers. The correspond-
ing pair of flyback and ground clamp diodes conduct after the
drivers are disabled, resulting in fast current decay. When the
device is enabled, the internal current control circuitry will be
active and can be used to limit the load current in a slow-decay
mode.
For applications that PWM the ENABLE input, and desire that
the internal current limiting circuit function in the fast-decay mode,
the ENABLE input signal should be inverted and connected to
the MODE input. This prevents the device from being switched
into sleep mode when the ENABLE input is low.
(2) PHASE Pulse-Width Modulation
Toggling the PHASE terminal determines/controls which sink/
source pair is enabled, producing a load current that varies with
the duty cycle and remains continuous at all times. This can
have added benefits in bidrectional brush dc servo motor appli-
cations as the transfer function between the duty cycle on the
phase input and the average voltage applied to the motor is
more linear than in the case of ENABLE PWM control (which
produces a discontinuous current at low current levels). See
also, “DC Motor Applications” below.
(3) SYNCHRONOUS FIXED-FREQUENCY PWM
The internal PWM current-control circuitry of multiple A3952S-
devices can be synchronized by using the simple circuit shown
in figure 3. A555IC can be used to generate the reset pulse/
t
1
RC
N
(G)MISCELLANEOUS INFORMATION
A logic high applied to both the ENABLE and MODE terminals
puts the device into a sleep mode to minimize current consump-
tion when not in use.
An internally generated dead time prevents crossover currents
that can occur when switching phase or braking.
Thermal protection circuitry turns OFF all drivers should the junc-
tion temperature reach 165°C (typical). This is intended only to
protect the device from failures due to excessive junction tem-
peratures and should not imply that output short circuits are
permitted. The hysteresis of the thermal shutdown circuit is ap-
proximately 15°C.
If the internal current-control circuitry is not used; the V
REF
ter-
minal should be connected to V
CC
, the SENSE terminal should
be connected to ground, and the RC terminal should be left
floating (no connection).
An internal under-voltage lockout circuit prevents simultaneous
conduction of the outputs when the device is powered up or
powered down.
74
A3952SB/SLB/SW