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Discontinued Product: Use this replacement. http://www.panucatt.com/product_p/sd8825.htm

The SureStepr SD82A/82B are stepper motor drivers with the A4982 chip from Allegro Micro(models vary only in IC package). They are simple to use and operate using an indexer (DIR/STEP) interface to move the stepper motors. The SD82A/82B are drop in replacements for Pololu style footprint drivers including the A4988, A4983 and Stepsticks (motor pinouts are reversed compared to Pololu and Stepstick drivers see user guide).

The SD82A/82B has a distinct design feature not found on similar drivers, the components are mounted on the underside of the PCB. The driver chip has a heat pad at the bottom of case that allows heat to be drawn away from it. By having the parts at the bottom you can now attach a heatsink that is thermally connected to the heat pad thereby cooling the chip better compared to attaching the heat sink on top of the IC, Heat dissipation will be different for every setup but a heat sink may not be required for current limits of 1.2Amps and below, assess your install if you require one. The SD82A/82B also uses a 4 layer PCB with 2oz copper thickness which helps in moving heat away from the chip.

The SD82A/82B comes pre-soldered with special 0.1” pitch headers that are taller than what is commonly available. This gives more space at the bottom to protect the parts from shorting into something and allows air to flow more freely on the underside of the board.