PBL 3775/1
Low inductance, especially in combi-
nation with a high supply voltage,
enables high stepping rates. However,
to give the same torque capability at low
speed, the reduced number of turns in
the winding in the low resistive, low
inductive motor must be compensated
by a higher current. A compromise has
to be made. Choose a motor with the
lowest possible winding resistance and
inductance, that still gives the required
torque, and use as high supply voltage
as possible, without exceeding the
maximum recommended 40 V. Check
that the chopping duty cycle does not
exceed 50 % at maximum current.
Heat sinking
PBL 3775/1 is a power IC, packaged in
a power DIP,SO or PLCC package. The
ground leads of the package (the
batwing) are thermally connected to the
chip. External heatsinking is achieved
by soldering the ground leads onto a
copper ground plane on the PCB.
Maximum continuous output current is
heavily dependent on the heatsinking
and ambient temperature. Consult
figures 8, 9 and 14 to determine the
necessary heatsink, or to find the
maximum output current under varying
conditions.
A copper area of 20 cm
2
(approx. 1.8”
x 1.8”), copper foil thickness 35
µm
on a
1.6 mm epoxy PCB, permits the circuit
to operate at 2 x 450 mA output current,
at ambient temperatures up to 85° C.
Thermal shutdown
The circuit is equipped with a thermal
shutdown function that turns the outputs
off at a chip (junction) temperature
above 160° C. Normal operation is
resumed when the temperature has
decreased about 20° C.
Programming
Figure 15 shows the different input and
output sequences for full-step, half-step
and modified halfstep operations.
Full-
step mode.
Both windings are
energized at all the time with the same
current, I
M1
= I
M2
. To make the motor
take one step, the current direction (and
the magnetic field direction) in one
phase is reversed. The next step is then
taken when the other phase current
reverses. The current changes go
through a sequence of four different
states which equal four full steps until
the initial state is reached again.
P
D
(W)
6
Maximum allowable power dissipation [W]
3.0
5
pi
ing
Batw
4
Am
bie
nt
t
em
2.0
3
pe
ra
tu
re
re
ratu
mpe
n te
1.0
o
Tw
ls
ne
an
ch
on
2
1
0
0
O
ha
ne c
0.20
nne
l on
0
-25
0
25
50
75
100
125
150
Temperature [°C]
0.40
0.60
0.80
I
M
(A)
PLCC package
DIP package
All ground pins soldered onto a
20 cm
2
PCB copper area with
free air convection.
Figure 8. Power dissipation vs. motor
current.T
a
= 25
°
C.
V
CE Sat
(V)
Figure 9. Maximum allowable power
dissipation.
V
d, ld
(V)
1.2
1.0
0.8
0.6
0.4
0.2
1.2
1.0
0.8
0.6
0.4
0.2
0
0
0.20
0.40
0.60
0.80
0
0
0.20
0.40
0.60
0.80
I
M
(A)
I
M
(A)
Figure 10. Typical lower transistor
saturation voltage vs. output current.
V
CE Sat
(V)
Figure 11. Typical lower diode voltage
drop vs. recirculating current.
V
d, ud
(V)
1.2
1.0
0.8
0.6
0.4
0.2
1.2
1.0
0.8
0.6
0.4
0.2
0
0
0.20
0.40
0.60
0.80
0
0
0.20
0.40
0.60
0.80
I
M
(A)
I
M
(A)
Figure 12. Typical upper transistor
saturation voltage vs. output current.
Figure 13. Typical upper diode voltage
drop vs. recirculating current.
7
ERICSSON [ ERICSSON ]
