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 = (

(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 700

Ω (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 :

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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