5804 BiMOS II UNIPOLAR STEPPER-MOTOR TRANSLATOR/DRIVERAPPLICATIONS INFORMATIONWAVE-DRIVE SEQUENCEHalf Step = L, One Phase = H Internal power-on reset (POR) circuitry resets OUTPUTA (and OUTPUTD in the two-phase StepABCD drive format) to the on state with initial applica- POR ON OFF OFF OFF tion of the logic supply voltage. After reset, the 1 ON OFF OFF OFF circuit then steps according to the tables. 2 OFF ON OFF OFF The outputs will advance one sequence 3 OFF OFF ON OFF position on the high-to-low transition of the STEP 4 OFF OFF OFF ON INPUT pulse. Logic levels on the HALF-STEP and ONE-PHASE inputs will determine the drive format (one-phase, two-phase, or half-step). The DIRECTION pin determines the rotation se- TWO-PHASE DRIVE SEQUENCE quence of the outputs. Note that the STEP Half Step = L, One Phase = L INPUT must be in the low state when changing the state of ONE-PHASE, HALF-STEP, or StepABCD DIRECTION to prevent erroneous stepping. POR ON OFF OFF ON 1 ON OFF OFF ON All outputs are disabled (off) when OUTPUT 2 ON ON OFF OFF ENABLE is at a logic high. If the function is not 3 OFF ON ON OFF required, OUTPUT ENABLE should be tied low. 4 OFF OFF ON ON In that condition, all outputs depend only on the state of the step logic. During normal commutation of a unipolar stepper motor, mutual coupling between the HALF-STEP DRIVE SEQUENCE motor windings can force the outputs of the Half Step = H, One Phase = L UCN5804B below ground. This condition will cause forward biasing of the collector-to-substrate StepABCD junction and source current from the output. For POR ON OFF OFF OFF many L/R applications, this substrate current is 1 ON OFF OFF OFF high enough to adversely affect the logic circuitry 2 ON ON OFF OFF and cause misstepping. External series diodes 3 OFF ON OFF OFF (Schottky are recommended for increased 4 OFF ON ON OFF efficiency at low-voltage operation) will prevent 5 OFF OFF ON OFF substrate current from being sourced through the 6 OFF OFF ON ON outputs. Alternatively, external ground clamp 7 OFF OFF OFF ON diodes will provide a preferred current path from 8 ON OFF OFF ON ground when the outputs are pulled below ground. Internal thermal protection circuitry disables all outputs when the junction temperature reaches approximately 165°C. The outputs are enabled again when the junction cools down to approxi- mately 145°C. 115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000
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