A4988 stepper driver: specs and pinout
Microstepping DMOS driver for bipolar stepper motors, with step and direction control and a set current limit up to 2 A.
Specs
| Spec | Value | Source |
|---|---|---|
| Logic supply VDD | 3 V to 5.5 V | source Electrical Characteristics, Logic Supply Voltage Range (p.4) |
| Load (motor) supply VBB | 8 V to 35 V | source Electrical Characteristics, Load Supply Voltage Range (p.4) |
| Output current | +/-2 A | source Features and description (p.1) |
| Current limit formula | ITripMAX = VREF / (8 x RS), RS in ohms | source Current control section (p.9) |
| Logic supply current IDD (outputs off) | 5 mA max | source Electrical Characteristics, Logic Supply Current (p.4) |
| Step modes | full, 1/2, 1/4, 1/8, 1/16 step | source Features (p.1) |
| Protection | thermal shutdown, undervoltage lockout (UVLO), crossover-current protection | source Features (p.1); protection (p.2) |
| Logic compatibility | 3.3 V and 5 V compatible logic supply | source Features (p.1) |
Power
| Value | Source | |
|---|---|---|
| Supply | VDD 3-5.5 V (logic); VBB 8-35 V (motor) | source Electrical Characteristics (p.4) |
| Current | IDD 5 mA max (outputs off) | source Electrical Characteristics (p.4) |
Chip pins
These are the pins of the chip on the module, from the chip datasheet. The module's own header may label or expose them differently. Module header labels come from the Compoden listing, not an official module schematic.
| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| VDD | Logic supply | 3-5.5 V; absolute max 5.5 V | Module label VDD (listing). | source Terminal List Table; Electrical Characteristics; Absolute Maximum Ratings |
| VBB1 / VBB2 | Load (motor) supply; chip label VBB, listing label VMOT | 8-35 V; absolute max 35 V | Datasheet decoupling: 100 uF near the supply (typical application). VMOT = VBB is by name/role only. | source Terminal List Table; Electrical Characteristics; Absolute Maximum Ratings |
| GND | Ground (two pins) | 0 V | source Terminal List Table | |
| STEP | Logic input: a low-to-high transition advances the motor one increment | Logic input: VIH min 0.7 x VDD, VIL max 0.3 x VDD; absolute max -0.3 to 5.5 V | source Terminal List Table; Functional description | |
| DIR | Logic input: sets direction of rotation; takes effect on next STEP rising edge | Logic input: VIH min 0.7 x VDD, VIL max 0.3 x VDD; absolute max -0.3 to 5.5 V | source Terminal List Table; Functional description | |
| ENABLE | Logic input: logic high disables the outputs, logic low enables them | Logic input: VIH min 0.7 x VDD, VIL max 0.3 x VDD; absolute max -0.3 to 5.5 V | The listing says the enable pin can be tied low to enable the driver; this matches the datasheet. | source Terminal List Table; Functional description |
| MS1, MS2, MS3 | Microstep select inputs (Table 1: LLL full, HLL 1/2, LHL 1/4, HHL 1/8, HHH 1/16) | Logic input: VIH min 0.7 x VDD, VIL max 0.3 x VDD; absolute max -0.3 to 5.5 V | MS1 and MS3 have 100 k pull-down, MS2 has 50 k pull-down. | source Terminal List Table; Table 1 (p.6) |
| RESET | Logic input, active low: sets translator to Home state and turns off all FET outputs | Logic input: VIH min 0.7 x VDD, VIL max 0.3 x VDD; absolute max -0.3 to 5.5 V | STEP inputs are ignored while RESET is low. | source Terminal List Table; Functional description |
| SLEEP | Logic input, active low: sleep mode; high allows normal operation | Logic input: VIH min 0.7 x VDD, VIL max 0.3 x VDD; absolute max -0.3 to 5.5 V | Allow 1 ms after leaving sleep before issuing a STEP. | source Terminal List Table; Functional description |
| REF (VREF) | Reference voltage input that sets the current limit: ITripMAX = VREF / (8 x RS) | Absolute max 5.5 V | Listing label Vref. | source Terminal List Table; Absolute Maximum Ratings |
| OUT1A, OUT1B, OUT2A, OUT2B | DMOS full-bridge outputs to the two motor coils | Output absolute max -2.0 to 37 V; +/-2 A | source Terminal List Table; Absolute Maximum Ratings | |
| SENSE1, SENSE2 | Sense resistor terminals for bridges 1 and 2 | Absolute max -0.5 to 0.5 V | source Terminal List Table; Absolute Maximum Ratings |
Common mistakes
- Setting the current with the wrong sense resistor: the limit is ITripMAX = VREF / (8 x RS), so RS must be the value on your board (source)
- Running the motor supply below 8 V: the load supply range is 8-35 V (source)
- Relying on the chip for fault protection: the datasheet lists thermal shutdown, UVLO and crossover-current protection only (source)
What we could not confirm
- Sense resistor values (0.05 or 0.1 ohm on the listing) are board-specific and not in the datasheet.
- Module overcurrent protection wording from the listing is not used; the datasheet's protection list applies.
- Module pinout and heat-sink needs are not covered by the chip datasheet.
- Pin rows are the A4988 chip pins; the listing names only VMOT, GND, VDD, STEP, DIR, an unnamed enable pin and Vref. Whether the module breaks out MS1-MS3, RESET, SLEEP and OUT pins, and the sense resistor value, are unsourced.
- Chip logic inputs are absolute max 5.5 V and VDD is 3-5.5 V, so 3.3 V and 5 V logic both work when VDD matches; the module label 'VDD' is the logic supply, VMOT is the motor supply (8-35 V).
Sources
- link (Allegro A4988 DMOS Microstepping Driver, 4988-DS Rev. 8)
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