A4988

The DRV8825 is the stronger part on paper: 8.2 V to 45 V versus 35 V, 2.5 A versus 2 A, 1/32 microstepping versus 1/16, a DECAY pin for explicit slow, fast or mixed decay, and an internal 3.3 V reference output. The A4988 is simpler and needs no decay tuning. The two share the common 16-pin carrier footprint but are not electrically interchangeable: the current formula changes from ITripMAX = VREF / (8 × RS) on the A4988 to ITripMAX = VREF / (5 × RS) on the DRV8825, carrier sense resistors differ (typically 0.05 ohm versus 0.25 ohm), and the microstep truth table diverges above 1/8 step. Always recalibrate VREF and re-check the MODE pins when swapping.

Use ITripMAX = VREF / (8 × RS), where RS is the effective resistance of the sense resistor network on each bridge. On a standard carrier with two 0.1 ohm resistors in parallel, RS = 0.05 ohm and the formula reduces to current limit ≈ VREF × 2.5. Turn the trimmer while monitoring the voltage at VREF with a multimeter, aim for about 70 to 80 percent of the motor's rated current, and never exceed the ±0.5 V absolute maximum on the sense pins. Setting the limit too high is the most common cause of A4988 thermal failure on printer boards.

Not directly. The A4988 is a bipolar driver: its two full bridges expect a four-wire motor with both ends of each winding accessible. A five- or six-wire unipolar motor has centre taps and is normally driven by sinking current from one half-winding at a time. You can convert a unipolar motor to bipolar by ignoring the centre taps and using the full winding (halves the current rating, doubles inductance), but for genuine unipolar drive use a ULN2803 or ULN2003 Darlington array, or an L298N with the centre taps tied to the motor supply, sequenced by the MCU or an L297.

Thermal, not electrical. The ±2 A figure is an absolute maximum, and reaching it depends entirely on the exposed pad. Junction-to-ambient is 32 °C/W on a four-layer JEDEC board, and the fused pins 3 and 18 must be soldered to a copper pour with an array of thermal vias into inner layers. On a single-sided breakout with no pour you will thermal-limit near 1 A. Add copper, add airflow, drop VREF, or move to a higher-current part such as the DRV8825 or TMC2209 with better Ron.

Yes. Both are active-low with internal pulldowns, so if they float the device stays disabled or asleep and STEP does nothing. Commercial modules tie RESET and SLEEP together and pull them to VDD through a resistor; on a bare IC design, drive them from spare GPIOs if you want power management, or tie them high permanently. Likewise ENABLE is active-low — leave it low to keep the bridges on.

Smoother motion, lower audible noise and reduced mid-range resonance, because each electrical cycle is divided into 64 steps instead of 4. It does not improve absolute positioning accuracy: incremental torque per microstep falls to about 10 percent of holding torque at 1/16, so load friction and detent torque dominate. For a printer or CNC it is worthwhile for surface finish and noise; for a high-inertia load it may not move the rotor at all at fine resolution.

Test functionally rather than visually. Set VREF to a known value, put a 0.05 ohm-equivalent sense network in place, and measure full-step winding current: genuine Allegro parts hold the specified ±5 percent trip accuracy at the 100 percent current setting, clones often miss by 30 percent. Then walk MS1/MS2/MS3 through all five modes and confirm the phase waveforms on a scope — remarked dies frequently only do full and half step. Visually, look for laser-etched Allegro marking, a consistent QFN body size of 5 × 5 × 0.90 mm and a properly exposed thermal pad. We sample-test every reel.

MOQ is one reel of A4988SETTR-T (1500 pcs, 28-contact QFN) for volume, or 50 pcs loose and assembled modules in packs of 10 for prototyping. Shenzhen stock ships in one to two business days. Allegro authorized-channel lead time is twelve to twenty weeks, so keep a DRV8825 or TMC2209 as a qualified alternate on your AVL.