The A4987 is a dual DMOS full-bridge stepper motor driver with parallel input communication and overcurrent protection. Each full-bridge output is rated up to 35 V and ±1 A. The A4987 includes fixed off-time pulse width modulation (PWM) current regulators, along with 2- bit nonlinear DACs (digital-to-analog converters) that allow stepper motors to be controlled in full, half, and quarter steps. The PWM current regulator uses the Allegro® patented mixed decay mode for reduced audible motor noise, increased step accuracy, and reduced power dissipation.
Internal synchronous rectification control circuitry is provided to improve power dissipation during PWM operation.
The outputs are protected from shorted load and short-toground events, which protect the driver and associated circuitry from thermal damage or flare-ups. Other protection features include thermal shutdown with hysteresis, undervoltage lockout (UVLO) and crossover current protection. Special power-up sequencing is not required.
The A4987 is supplied in two packages, a 24-contact QFN (ES) and a 24-pin TSSOP (LP). Both packages have exposed thermal pads for enhanced thermal performance. The 24-contact ES is 4 mm × 4 mm, with a nominal overall package height of 0.75 mm. The 24-pin LP is a TSSOP with 0.65 pitch and an overall package height of ≤1.2 mm. Both packages are lead (Pb) free, with 100% matte tin leadframe plating.
