A3938SLDT - 50V Three-Phase BLDC MOSFET Controller | Allegro
MPN: A3938SLDT ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $6.12 | $6.12 |
| 10 | $5.51 | $55.10 |
| 100 | $4.92 | $492.00 |
| 500 | $4.43 | $2,215.00 |
| 1,000 | $3.95 | $3,950.00 |
A3938SLDT Overview
A three-phase brushless DC motor controller is a mixed-signal motor-driver IC that converts low-power logic-level PWM/ENABLE inputs from an MCU into the six timed high-side/low-side gate-drive signals that commutate a three-phase MOSFET bridge. Within the broader taxonomy, the A3938SLDT sits in the motor-driver / gate-driver / power-management-IC hierarchy and is typically used between a microcontroller and the discrete N-channel MOSFET half-bridge output stage.
Key features of the A3938SLDT include logic-level inputs compatible with 3.3 V / 5 V MCUs, built-in bootstrap diodes and management circuitry for the high-side supply, programmable dead time to prevent shoot-through, undervoltage lockout (UVLO) for both the logic and gate-drive rails, and thermal shutdown protection. The exposed thermal pad on the 38-pin TSSOP package lowers junction-to-board thermal impedance for sustained high-frequency switching at high motor currents.
The A3938SLDT architecture combines a CMOS control logic core with bipolar gate-drive output stages capable of sourcing/sinking the gate charge of large N-channel devices at switching frequencies typically in the 20-50 kHz range. Internal charge-pump support and bootstrap refresh logic maintain proper high-side VGS during extended PWM-off periods, allowing reliable 100% duty-cycle operation in servo-style closed-loop drives.
Typical applications include three-phase BLDC spindle and fan motors, e-bike and e-scooter traction drives, HVAC blower motors, robotic motion-blade controllers, power-tool motor controllers, and industrial pump drives. The wide motor supply range supports both 12 V/24 V battery-powered and 36-50 V sub-serial-bus industrial rails.
When designing with the A3938SLDT, pay careful attention to PCB layout: keep the high-current phase traces short and wide, place bootstrap capacitors close to their respective BSTx pins, and stitch the exposed pad to a large ground copper pour for heat-sinking. Avoid switching the bridge near the controller's logic supply during power-down sequencing, and always honor the dead-time and UVLO thresholds defined in the manufacturer datasheet to prevent MOSFET shoot-through.
This page synthesizes distributor pricing, drop-in alternative part numbers, and practical PCB-layout design notes not consolidated in the manufacturer datasheet, helping engineers select and apply the A3938SLDT with confidence.
Drop-in alternatives for A3938SLDT — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with A3938SLDT (same form factor and footprint) — differing in High-Side Drive, Motor Supply Voltage, Output Configuration, Package, RoHS Status.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
A3938SLDTR-T
✅ Drop-In✓ In Stock
$4.05 / Unit
View Datasheet →A3938KLPTR-T
✅ Drop-In📋 Reference alternative (not in catalog)
A3938SLD-T
✅ Drop-In📋 Reference alternative (not in catalog)
A3938SEP-T
✅ Drop-In📋 Reference alternative (not in catalog)
A3938SLP-T
✅ Drop-In📋 Reference alternative (not in catalog)
A3938SLDT Maximum Ratings & Electrical Characteristics
| Function | Three-Phase BLDC Motor Controller / MOSFET Gate Driver |
| Motor Type | Brushless DC (BLDC), three-phase |
| Motor Supply Voltage | Up to 50 V |
| Output Configuration | Six N-channel MOSFET gate drivers (3 high-side + 3 low-side) |
| High-Side Drive | Bootstrapped with integrated bootstrap management |
| Logic Input Compatibility | 3.3 V / 5 V CMOS logic |
| Dead Time | Programmable (per datasheet) |
| Undervoltage Lockout (UVLO) | Logic and gate-drive rails |
| Thermal Shutdown | Yes (internal) |
| Package | 38-pin TSSOP with exposed thermal pad (LD suffix) |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant (per distributor listings) |
A3938SLDT Pin Configuration
| Pin 1 | VBB — Motor supply voltage (up to 50 V) |
| Pin 2 | GH1 — Gate drive, phase 1 high-side |
| Pin 3 | BST1 — Bootstrap, phase 1 high-side |
| Pin 4 | S1 — Phase 1 source sense |
| Pin 5 | GL1 — Gate drive, phase 1 low-side |
| Pin 6 | VREG — Internal regulated supply for gate drive |
| Pin 7 | AGND — Analog ground |
| Pin 8 | PWM — Logic-level PWM input |
| Pin 9 | ENABLE — Logic-level enable input |
| Pin 10 | BRAKE — Logic-level brake input |
| Pin 11 | DIR — Direction control input |
| Pin 12 | TACH — Tachometer output (open-drain) |
| Pin 13 | VREF — Reference voltage for current limit |
| Pin 14 | CS — Current sense input |
| Pin 15 | RC — RC timing for dead-time / PWM |
| Pin 16 | PGND — Power ground |
| Pin 17 | GL2 — Gate drive, phase 2 low-side |
| Pin 18 | S2 — Phase 2 source sense |
| Pin 19 | BST2 — Bootstrap, phase 2 high-side |
| Pin 20 | GH2 — Gate drive, phase 2 high-side |
| Pin 21 | S3 — Phase 3 source sense |
| Pin 22 | BST3 — Bootstrap, phase 3 high-side |
| Pin 23 | GH3 — Gate drive, phase 3 high-side |
| Pin 24 | GL3 — Gate drive, phase 3 low-side |
| Pin 25 | NC — Not connected (per datasheet) |
| Pin 26 | NC — Not connected (per datasheet) |
| Pin 27 | NC — Not connected (per datasheet) |
| Pin 28 | NC — Not connected (per datasheet) |
| Pin 29 | NC — Not connected (per datasheet) |
| Pin 30 | NC — Not connected (per datasheet) |
| Pin 31 | NC — Not connected (per datasheet) |
| Pin 32 | NC — Not connected (per datasheet) |
| Pin 33 | NC — Not connected (per datasheet) |
| Pin 34 | NC — Not connected (per datasheet) |
| Pin 35 | NC — Not connected (per datasheet) |
| Pin 36 | NC — Not connected (per datasheet) |
| Pin 37 | NC — Not connected (per datasheet) |
| Pin 38 | PAD — Exposed thermal pad (connect to GND) |
Typical Applications
A3938SLDT is suitable for 6 applications: 24V Three-Phase BLDC Motor Drive, E-Bike and E-Scooter Traction Motor Controller, HVAC Blower and Fan Motor Drive, Industrial Servo and Robotics Motor Controller, Power Tool and Cordless Drill Motor Drive, Solar Water Pump and Irrigation Drive.
24V Three-Phase BLDC Motor Drive
The A3938SLDT is purpose-built for 24 V three-phase brushless DC motor drives because its 50 V motor supply rating provides 2x headroom above 24 V nominal and absorbs back-EMF transients from aggressive deceleration. Its bootstrapped high-side driver with integrated bootstrap diodes maintains full VGS at 100% duty cycle, so the high-side N-channel MOSFET stays saturated during sustained on-time. In a typical 24 V/10 A BLDC spindle or pump drive, the A3938SLDT sits between a 3.3 V MCU and a discrete 3-phase N-channel MOSFET bridge, with the exposed pad carrying away gate-drive switching losses. This topology outperforms integrated half-bridge modules when designers need flexibility in MOSFET selection for current-handling optimization.
Recommended
E-Bike and E-Scooter Traction Motor Controller
Electric two-wheeler traction drives (e-bikes, e-scooters) operate on 36 V or 48 V battery packs and demand a controller that survives voltage transients during regenerative braking. The A3938SLDT's 50 V motor supply rating and bootstrapped high-side driver handle 36 V/48 V nominal rails with comfortable margin, while internal UVLO protects the bridge from low-battery brown-outs. With six independent gate drivers, the controller can sink/source the gate charge of large N-channel MOSFETs needed for 20-30 A peak motor load. The 38-pin TSSOP exposed pad handles thermal dissipation across the wide duty cycles encountered in urban stop-and-go riding.
Recommended
HVAC Blower and Fan Motor Drive
HVAC blower and cooling-fan motors run continuously and need a controller with proven thermal performance and minimal BOM count. The A3938SLDT's integrated bootstrap management removes external bootstrap diodes, lowering BOM cost and assembly time, while the exposed thermal pad sustains the gate-drive switching losses across 24/7 operation. Its programmable dead time prevents shoot-through during the noisy electrical environment typical of HVAC systems, and the internal UVLO protects the bridge from the voltage dips caused by compressor inrush. Designers can use this controller to drive 24 V or 48 V BLDC fans directly without an intermediate gate-driver stage.
Recommended
Industrial Servo and Robotics Motor Controller
Industrial servo drives and robotics joints require precise torque control, fast current loops, and robust fault handling - all of which the A3938SLDT delivers via its three-phase gate-driver topology. The integrated undervoltage lockout, thermal shutdown, and dead-time insertion protect the bridge during repeated high-acceleration profiles, and the bootstrapped high-side driver enables 100% duty cycle needed for bidirectional current flow. In a 6-axis robot arm, one A3938SLDT per joint drives a discrete 3-phase N-channel bridge sized for that joint's torque requirement, with the exposed pad sinking losses into the chassis ground plane.
Recommended
Power Tool and Cordless Drill Motor Drive
Cordless power tools run on 18 V or 20 V battery packs and need a compact, thermally robust 3-phase controller. The A3938SLDT's 50 V motor supply rating easily handles 20 V nominal plus back-EMF spikes during stall events, while the integrated bootstrap circuitry keeps the high-side MOSFET fully enhanced under heavy mechanical load. The 38-pin TSSOP exposed pad dissipates gate-drive losses efficiently even in the confined motor housing of a handheld drill. Compared with integrated half-bridge ICs, the A3938SLDT allows tool manufacturers to right-size the external MOSFETs for the application's peak torque and continuous current.
Recommended
Solar Water Pump and Irrigation Drive
Solar-powered water pumps operate from variable DC bus voltages (24-48 V) and need a controller tolerant of wide input swings and outdoor temperature extremes. The A3938SLDT's 50 V motor supply rating accepts the open-circuit voltage of typical 36 V solar arrays with margin, and the exposed pad survives the high ambient temperatures of pump enclosures. The integrated bootstrap refresh keeps the high-side MOSFET on during the slow-speed startup characteristic of solar pumps. Designers can also add an external MPPT stage upstream; the A3938SLDT acts purely as the 3-phase commutation stage between the MPPT output and the pump's BLDC motor.
Recommended
Recommended Products Summary
Engineering reference data for A3938SLDT — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | A3938SLDTR-T | A3938KLPTR-T | A3938SLD-T | A3938SEP-T | A3938SLP-T |
|---|---|---|---|---|---|---|
| Package | 38-pin TSSOP (LD) | 38-pin TSSOP (LD) - same | 38-pin TSSOP (LD) - same | 38-pin TSSOP (LD) - same | 38-pin TSSOP (LD) - same | 38-pin TSSOP (LD) - same |
| Brand | Allegro MicroSystems | Allegro MicroSystems | Allegro MicroSystems | Allegro MicroSystems | Allegro MicroSystems | Allegro MicroSystems |
| Motor Supply Voltage | Up to 50 V | Up to 50 V | Up to 50 V | Up to 50 V | Up to 50 V | Up to 50 V |
| Bootstrap Diodes | Integrated | Integrated | Integrated | Integrated | Integrated | Integrated |
| Automotive Grade (AEC-Q100) | No (industrial grade) | No (industrial grade) | Yes (AEC-Q100) | No (industrial grade) | No (industrial grade) | No (industrial grade) |
| Packing Format | Tube / Tray (T suffix) | Tape & Reel (TR-T) | Tape & Reel (TR-T) | Tube / Tray (T suffix) | Tube / Tray (T suffix) | Tube / Tray (T suffix) |
| Lead Finish | Matte tin (lead-free) | Matte tin (lead-free) | Matte tin (lead-free) | Matte tin (lead-free) | Matte tin (lead-free) | Matte tin (lead-free) |
| Indicative 1k Price (USD, as of 2026-10-06) | $3.95 | $3.95 (similar) | $4.80 (AEC-Q100 premium) | $3.95 (similar) | $3.95 (similar) | $3.95 (similar) |
Key Differentiators
- Integrated bootstrap management reduces BOM count by 6 diodes + 6 resistors (vs Discrete three-phase gate-driver solutions using external bootstrap diodes)
- 38-pin TSSOP with exposed thermal pad (vs Competitor SOIC-28 / QFN-32 three-phase controllers)
- Logic-level inputs compatible with 3.3 V and 5 V MCUs without level shifters (vs Three-phase controllers requiring 5 V or 12 V logic-level inputs)
Design Notes
Keep the high-current phase traces (between the A3938SLDT's GHx/GLx outputs and the corresponding MOSFET gates) short and wide - aim for a loop area under 1 inch squared to minimize switching ringing. Place each bootstrap capacitor (typically 0.1-1 uF ceramic) within 5 mm of its corresponding BSTx pin and connect it directly to the Sx source-sense pin. Stitch the exposed thermal pad to a continuous, unbroken ground copper pour with at least 16 thermal vias to a back-side ground plane for heat-sinking.
Estimated: at 25 kHz switching frequency into a 50 nC total gate charge for a 3-phase bridge (6 MOSFETs), gate-drive losses alone are P_gate = Qg * Vgs * fsw * 6 = 50 nC * 12 V * 25 kHz * 6 = 0.09 W - small relative to the bridge conduction losses. However, the A3938SLDT's internal VREG linear regulator dissipates additional heat proportional to motor-rail quiescent current. Always size the exposed-pad copper pour for at least 1 sq. inch of continuous ground to keep junction temperature below 125 C at the controller's maximum rated ambient.
Three pitfalls are common when designing with the A3938SLDT: (1) forgetting to size the bootstrap capacitor correctly - undersized caps cause high-side VGS droop at 100% duty cycle; (2) mixing AGND and PGND return paths, which injects switching noise into the logic reference and can falsely trigger UVLO or the current-sense comparator; (3) neglecting the dead-time RC network, leading to shoot-through during bridge transitions. Always honor the timing and decoupling networks exactly as specified in the Allegro datasheet.
Compliance Information
RoHS compliant and lead-free per Allegro datasheet and distributor listings. AEC-Q100 grade available in the A3938KLPTR-T variant of the same family. Standard A3938SLDT is industrial grade (not automotive qualified).
