Description

The LS8297 Stepper Motor Controller generates four phase drive signal outputs for controlling two phase Bipolar and four phase Unipolar motors. The outputs are used to drive two H-bridges for the two motor windings in the Bipolar motor or the four driver transistors for the two center-tapped windings in the Unipolar motor. The motor can be driven in full step mode either in normal drive (two-phase-on) or wave drive (one-phase-on) and half step mode. The LS8297 provides two inhibit outputs which are used to control the driver stages of each of the motor phases. The circuit uses STEP, FRD/REV and HALF/FULL inputs in a translator to generate controls for the output stages.

A dual PWM chopper circuit using an on-chip oscillator, latches and voltage comparators are used to regulate the current in the motor windings. For each pair of phase driver outputs (PHA, PHB, and PHC, PHD) each pulse of the common internal oscillator sets the latch and enables the output. If the current in the motor winding causes the voltage across a sense resistor to exceed the reference voltage, VREF, at the comparator inputs, the latch is reset disabling the output until the next oscillator pulse.

The CONTROL input determines whether the chopper acts on the phase driver outputs or the inhibit outputs. When the phase lines are chopped, the non-active phase line of each pair (PHA, PHB or PHC, PHD) is activated rather than de-activating the active line to reduce dissipation in the load sensing resistors. If PHA is high and PHB is low, current flows through Q1, motor winding, Q4 and sense resistor Rs. When chopping occurs, PHB is brought high and circulating current flows through Q1 and D3 and not through Rs resulting in less power dissipation in Rs. Current decay is slow using this method. When the Control input is brought low, chopping occurs by bringing INH1 low. In this case circulating current flows through D2, motor winding and D3 and through the power supply to ground causing the current to decay rapidly. For Unipolar motors, only inhibit chopping is used. When INH1 is brought low current in either half of the center tapped motor winding recirculates through the diode across it.

LS8297CT is the torque ripple compensated version of the LS8297. Torque imbalance resulting from alternating “one-phase on”, “two-phase on” sequence of the half-step mode is eliminated in the LS8297CT by switching the sense reference voltage between 100% and 70.7% in alternate steps.

Features:

• Low cost, low current, pin-compatible replacement for LS7297
• Torque Ripple Compensated half-steps – LS8297CT
• Controls two-phase Bipolar and four-phase Unipolar motors
• Interface to four AND Gates driving four N-Channel MOSFET’s for Unipolar motors
• Normal/wave drive
• PWM chopper circuit for current control
• Two over current sense comparators with external references input
• All inputs and outputs TTL/CMOS compatible (TTL for 5V operation)
• Supply current: < 400uA
• Supply voltage: 4.75 to 7V