Stepper motor enable line
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. SLEEP control.

How it works:


When STEP goes low D1 discharges C1. Q2 turns off and R2 pulls /SLEEP high enabling the output.
When STEP stops high C1 charges through R1, Q2 turns on and the stepper goes into sleep mode.
C1 can only be discharged to about 0.5 V with D1 and that would tend to turn on Q2. Adding D2 prevents this happening (hopefully).


Choose C1 so that R1 x C1 is the time delay you require.