The circuit is intended to drive both windings of a bipolar stepper motor.
The peak current control is generated through switch mode regulation.There is a choice of
three different current levels with the two logic inputs I01 - I11 for winding 1 and I02 - I12 for
The current can also be switched off completely.
Input logic (I0 and I1)
The current level in the motor winding is selected with these inputs. (See Figure 4). If any of
the logic inputs is left open, the circuit will treat it has a high level input.
Low current 1/3 IO max
Medium current 2/3 IO max
Maximum current IO max
This input determines the direction of current flow in the windings, depending on the motor
connections. The signal is fed through a Schmidt-trigger for noise immunity, and through a
time delay in order to guarantee that no short-circuit occurs in the output stage during
phase-shift.High level on the PHASE input causes the motor current flow from Out A
through the winding to Out B.
This part contains a current sensing resistor (RS), a low pass filter (RC, CC) and three
comparators. Only one comparator is active at a time. It is activated by the input logic
according to the current level chosen with signals Io and I1. The motor current flows through
the sensing resistor RS. When the current has increased so that the voltage across RS
becomes higher than the reference voltage on the other comparator input, the comparator
goes high, which triggers the pulse generator.
The max peak current Imax can be defined by: