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PDF PBL3717-2 Data sheet ( Hoja de datos )
| Número de pieza | PBL3717-2 | |
| Descripción | Stepper Motor Drive Circuit | |
| Fabricantes | Ericsson | |
| Logotipo |  |
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PBLAp3ri7l 11979/72
PBL 3717/2
Stepper Motor
Drive Circuit
Description
PBL 3717/2 is a bipolar monolithic circuit intended to control and drive the current in
one winding of a stepper motor.
The circuit consists of a LS-TTL compatible logic input stage, a current sensor, a
monostable multivibrator and a high power H-bridge output stage with built-in
protection diodes.
Two PBL 3717/2 and a small number of external components form a complete
control and drive unit for LS-TTL or microprocessor-controlled stepper motor systems.
Key Features
• Half-step and full-step modes.
• Switched mode bipolar constant
current drive.
• Wide range of current control
5 - 1200 mA.
• Wide voltage range 10 - 50 V.
• Designed for unstabilized motor supply
voltage.
• Current levels can be selected in steps
or varied continuously.
• Thermal overload protection.
Phase
I1
I0
VR
VCC
Schmitt
Trigger
Time
Delay
1
1
VMM
VMM
1
&&&&
≥1
≥1
MA
MB
GND
+
–
+
–
+
–
Current Sensor
C
Figure 1. Block diagram.
Output Stage
Monostable
t
off
=
0.69
•
R•
T
CT
TE
PBL 3717/2
16-pin plastic
batwing DIP
28-pin plastic
PLCC package
PBL 3717/2
20-pin SO wide
batwing package
1
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1 page  
PBL 3717/2
Functional Description
The PBL 3717/2 is intended to drive a
bipolar constant current through one
motor winding of a 2-phase stepper
motor.
Current control is achieved through
switched-mode regulation, see figure 5
and 6.
Three different current levels and zero
current can be selected by the input logic.
The circuit contains the following
functional blocks:
• Input logic
• Current sense
• Single-pulse generator
• Output stage
Input logic
Phase input. The phase input determines
the direction of the current in the motor
winding. High input forces the current
from terminal MA to MB and low input from
terminal M to M . A Schmitt trigger
BA
provides noise immunity and a delay
circuit eliminates the risk of cross
conduction in the output stage during a
phase shift.
Half- and full-step operation is possible.
Current level selection. The status of I
0
and I1 inputs determines the current level
in the motor winding. Three fixed current
levels can be selected according to the
table below.
Motor current
I0
High level 100% L
I1
L
Medium level 60% H L
Low level 20% L
H
Zero current 0% H H
The specific values of the different current
levels are determined by the reference
voltage VR together with the value of the
sensing resistor RS.
The peak motor current can be calculated
as follows:
im = (VR • 0.083) / RS [A], at 100% level
im = (VR • 0.050) / RS [A], at 60% level
im = (VR • 0.016) / RS [A], at 20% level
The motor current can also be
continuously varied by modulating the
voltage reference input.
| V MA – VMB |
50 %
t on
t off
V
CH
VE
td
t
fs=
1
ton + toff
D=
ton
ton + toff
t
Figure 4. Definition of terms.
Current sensor
The current sensor contains a reference
voltage divider and three comparators for
measuring each of the selectable current
levels. The motor current is sensed as a
voltage drop across the current sensing
resistor, RS, and compared with one of the
voltage references from the divider. When
the two voltages are equal, the
comparator triggers the single-pulse
generator. Only one comparator at a time
is activated by the input logic.
Single-pulse generator
The pulse generator is a monostable
multivibrator triggered on the positive
edge of the comparator output. The
multivibrator output is high during the
pulse time, toff , which is determined by the
timing components RT and CT.
toff = 0.69 • RT • CT
The single pulse switches off the power
feed to the motor winding, causing the
winding to decrease during toff.If a new
trigger signal should occur during toff , it is
ignored.
Output stage
The output stage contains four transistors
and four diodes, connected in an H-
bridge. The two sinking transistors are
used to switch the power supplied to the
motor winding, thus driving a constant
current through the winding. See figures 5
and 6.
Overload protection
The circuit is equipped with a thermal
shut-down function, which will limit the
junction temperature. The output current
will be reduced if the maximum permis-
sible junction temperature is exceeded. It
should be noted, however, that it is not
short circuit protected.
Operation
When a voltage VMM is applied across the
motor winding, the current rise follows the
equation:
im = (VMM / R) • (1 - e-(R • t ) / L )
R = Winding resistance
L = Winding inductance
t = time
(see figure 6, arrow 1)
The motor current appears across the
external sensing resistor, RS, as an
analog voltage. This voltage is fed
through a low-pass filter, RCCC, to the
voltage comparator input (pin 10). At the
moment the sensed voltage rises above
the comparator threshold voltage, the
monostable is triggered and its output
turns off the conducting sink transistor.
The polarity across the motor winding
reverses and the current is forced to
circulate through the appropriate upper
protection diode back through the source
transistor (see figure 6, arrow 2).
After the monostable has timed out, the
current has decayed and the analog
voltage across the sensing resistor is
below the comparator threshold level.
5
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