The circuit is intended to drive a bipolar constant current through one motor winding. The
constant current is generated through switch mode regulation.
There is a choice of three different current levels with the two logic inputs lN0 and lN1. The
current can also be switched off completely.
If any logic input is left open, the circuit treats it as a high-level input.
The PHASE input pin determines the direction of current flow in the winding, 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. A high level on the PHASE input causes the motor current flow from
OUTA through the winding to OUTB.
The lH0 and lH1 input pins select the current level in the motor winding. The values of the
different current levels are determined by the reference voltage VR together with the value of
the sensing resistor RS.
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 IN0 and IN1. 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 output goes high, which triggers the pulse generator and its output goes high
during a fixed pulse time (toff), thus switching off the power feed to the motor winding, and
causing the motor current to decrease during toff.