2-Phase Stepper Motor Bipolar Driver ICs (2-Phase/1-2 Phase Excitation)
A3953SB/SLB
sense resistor. The selected value of R
S
should not cause the
absolute maximum voltage rating of 1.0V (0.4V for
V
CC
=3.3Voperation), for the SENSE terminal, to be exceeded.
The current-sensing comparator functions down to ground al-
lowing the device to be used in microstepping, sinusoidal, and
other varying current-profile applications.
(B) Thermal Considerations.
For reliable operation it is recommended that the maximum junc-
tion termperature be kept below 110°C to 125°C. The junction
termperature can be measured best by attaching a thermocouple
to the power tab/batwing of the device and measuring the tab
temperature, T
TAB
. Tthe junction temperature can then be ap-
proximated by using the formula:
T
J
T
TAB
+ (I
LOAD
•
2
•
V
F
•
R
θ
JT
)
(C)PCB Layout.
The load supply terminal, V
BB
should be decoupled with an elec-
trolytic capacitor (>47
µ
F is recommeded) placed as close to the
device as is physically practical. To minimize the elffect of sys-
tem ground I
•
R drops on the logic and reference input signals,
the system ground should have a low-resistance return to the
motor supply voltage.
See also “Current Sensing” and “Thermal Considerations” above.
(D)Fixed Off-Time Selection.
With increasing values of t
OFF
, switching losses will decrease,
low-level load-current regulation will improve, EMI will be re-
duced, the PWM frequency will decrease, and ripple current will
increase. The value of t
OFF
can be chosen for optimization of
these parameters. For applications where audible noise is a
concern, typical values of t
OFF
are chosen to be in the range of
15 ms to 35 ms.
(E) Stepper Motor Applications.
The MODE terminal can be used to optimize the performance
of the device in microstepping/sinusoidal stepper-motor drive
applications. When the load current is increasing, slow decay
mode is used to limit the switching losses in the device and iron
losses in the motor. This also improves the maximum rate at
which the load current can increase (as compared to fast de-
cay) due to the slow rate of decay during t
OFF
.
When the load current is decreasing, fast-decay mode is used
to regulate the load current to the desired level. This prevents
tailing of the current profile caused by the back-EMF voltage of
the stepper motor.
where V
F
may be chosen from the electrical specification table
for the given level of I
LOAD
. The value for R
θ
JT
is given in the
package thermal resistance table for the appropriate package.
The power dissipation of the batwing packages can be improved
by 20% to 30% by adding a section of printed circuit board cop-
per (typically 6 to 18 square centimeters) connected to the
batwing terminals of the device.
The thermal performance in applications that run at high load
currents and/or high duty cycles can be improved by adding
external diodes in parallel with the internal diodes. In internal
PWM slow-decay applications, only the two ground clamp di-
odes need be added. For internal fast-decay PWM, or external
PHASE or ENABLE input PWM applications, all four external
diodes should be added for maximum junction temperature re-
duction.
Fig. 4 Example of Circuit (including GND) and GND Wiring Pattern
OUT
B
OUT
A
V
BB
+
A3953SLB
RC
REF
SENSE
Vref
Rt
R
S
Ct
V
BB
GND
A3953SLB
+
V
CC
GND
Phase
Enable
V
CC
4, 5,
12, 13
1Pin
Mode
Vref
V
BB
GND
V
CC
GND
Rt
Ct
Use jumper wiring
for dotted line.
66
A3953SB/SLB