LS7290-S, LS7290-TS, LS7290

The LS7290 generates Phase Drive outputs and PWM outputs for controlling two-phase Bipolar Motors or four-phase Unipolar Motors, respectively. The LS7290 contains a mode controlled look-up table for generating the motor duty cycle drive sequences. There are four outputs which are used to drive two H-Bridges for the two motor windings in the Bipolar motor or the four driver transistors for the two centertapped windings in the Unipolar motor. The LS7290 can step a motor in full steps and half steps. The refresh rate is set using an internal oscillator controlled by a crystal or by use of an external input clock. Typical refresh rate is equal to 31.25kHz with the clock frequency set at 8MHz. Peak-current feedback control using pulse-width modulation is used in full-step or half-step modes. The chopper consists of a voltage comparator, flip-flop and external sense resistor. The internal oscillator sets the flip-flop and enables the INH1 and INH2 outputs at the beginning of each PWM cycle. Once the peak motor current causes the voltage across the sense resistors to reach the voltage set by VREF, the outputs are disabled until the next oscillator pulse. The VREF voltage sets the peak current in each motor winding.