By substituting equations 1 and 2 into equation 3
and solving for the value of R1 the following equa-
tions for the external components can be derived :
1
R1 = ( – 2) R
IN
(4)
DC
T1
C1 = (5)
0.69 R1
Looking at equation 1 it can easily be seen that the
minimum pulse width of T2 will occur when the value
of R1 is at its minimum and the value of R1 at its
maximum. Therefore, when evaluating equation 4
the minimum value for R1 of 700Ω (1 KΩ – 30 %)
should be used to guarantee the required pulse
width.
Figure 1 : Oscillator Circuit and Waveforms.
APPLICATIONS INFORMATION
The circuits shown in figure 2 use the L6506 to im-
plement constant current drives for stepper motors.
Figure 2 shows the L6506 used with the L298 to
drive a 2 phase bipolar motor. The peak current can
be calculated using the equation :
V
ref
I
peak
=
R
sense
The circuit of Fig.2 can be used in applications re-
quiring different peak and hold current values by
modifying the reference voltage.
The L6506 may be used to implement either full step
or half step drives. In the case of 2 phase bipolar
stepper motor applications, if a half step drive is
used, the bridge requires an additional input to dis-
able the power stage during the half step. If used in
conjunction with the L298 the enable inputs may be
used for this purpose.
For quad darlington array in 4 phase unipolar motor
applications half step may be implemented using
the 4 phase inputs.
The L6506 may also be used to implement mi-
crostepping of either bipolar or unipolar motors.
L6506 -L6506D
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