A3938SLDTR-T - 3-Phase BLDC MOSFET Controller, 50V | Allegro
MPN: A3938SLDTR-T ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $6.24 | $6.24 |
| 10 | $5.78 | $57.80 |
| 100 | $5.21 | $521.00 |
| 500 | $4.62 | $2,310.00 |
| 1,000 | $4.05 | $4,050.00 |
A3938SLDTR-T Overview
What is a three-phase BLDC motor controller? A BLDC (brushless DC) controller is a power management IC that converts DC bus voltage into the six-step or sinusoidal commutation signals required by a three-phase stator. It sits in the broader power management hierarchy as: gate driver -> motor controller/driver -> power management IC -> semiconductor. By integrating bootstrap diodes for the floating high-side supply, the A3938 eliminates the discrete charge-pump circuitry normally required.
Key features include low-side synchronous rectification for reduced body-diode losses, adjustable dead time to prevent cross-conduction shoot-through, power MOSFET protection with fault reporting, and a wide operating voltage range from 18 V to 50 V. The PWM input accepts logic-level signals from a microcontroller or DSP. The 38-pin TSSOP package provides a manageable footprint while supporting the gate-drive current needed for high-current MOSFET bridges.
Technically, the A3938 uses a bootstrapped high-side driver topology where an internal diode and external capacitor create a floating supply above each phase voltage. Synchronous rectification turns ON the low-side switch during the off-time of the complementary switch, eliminating conduction through the MOSFET body diode and reducing switching losses. Dead time is programmable to balance shoot-through protection against body-diode conduction.
Typical applications include industrial BLDC servo drives, three-phase fans and pumps, e-bike and scooter traction controllers, CNC spindle drives, and robotic actuators. The 50 V ceiling also suits 36 V battery platforms and 48 V telecom / mild-hybrid auxiliary systems.
When designing with this device, ensure bootstrap capacitors are sized for the high-side switching frequency and that adequate bulk capacitance sits at the motor supply pins to absorb back-EMF transients. Verify thermal performance with the actual MOSFET gate charge and switching frequency, since the A3938 itself only dissipates the gate-drive power, while the external MOSFETs handle the bulk of motor power loss.
This page synthesizes distributor stock data, drop-in compatible alternatives, and design considerations not collected in the manufacturer datasheet.
Drop-in alternatives for A3938SLDTR-T — 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 A3938SLDTR-T (same form factor and footprint) — differing in Package, Motor Type, RoHS Status, Output Configuration, Synchronous Rectification.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
A3938SLD-T
✅ Drop-In📋 Reference alternative (not in catalog)
A3938SLD
✅ Drop-In📋 Reference alternative (not in catalog)
A4985SLDTR-T
✅ Drop-In📋 Reference alternative (not in catalog)
L6234
✅ Drop-In📋 Reference alternative (not in catalog)
L6398
✅ Drop-In📋 Reference alternative (not in catalog)
A3938SLDTR-T Maximum Ratings & Electrical Characteristics
| Function | Three-phase BLDC motor controller / MOSFET gate driver |
| Motor Supply Voltage | 18 V to 50 V |
| Topology | Three-phase, 6-step PWM / synchronous rectification |
| Number of Outputs | 3 half-bridge gate drive channels |
| Output Configuration | Pre-driver for N-channel MOSFETs (high-side + low-side) |
| High-Side Drive | Bootstrap with internal bootstrap diode |
| Synchronous Rectification | Yes (low-side) |
| Dead Time Adjustment | Adjustable (external resistor) |
| MOSFET Protection | Cross-conduction / shoot-through protection |
| PWM Input | Logic-level compatible |
| Package | 38-pin TSSOP (LD) |
| Mounting Type | Surface Mount |
| Packaging | Tape & Reel (TR) |
| Operating Temperature | -20C to +85C (industrial range per datasheet) |
| RoHS Status | Compliant (per Alldatasheet listing) |
A3938SLDTR-T Pin Configuration
| Pin 1 | VREG — Internal regulator output (5 V typical) |
| Pin 2 | VBB — Motor supply (18 V to 50 V) |
| Pin 3 | CP1 — Charge pump capacitor 1 |
| Pin 4 | CP2 — Charge pump capacitor 2 |
| Pin 5 | GND — Power ground |
| Pin 6 | DT — Dead time programming resistor |
| Pin 7 | TACH — Tachometer input |
| Pin 8 | BRAKE — Brake input (logic level) |
| Pin 9 | DIR — Direction input |
| Pin 10 | PWM — PWM input |
| Pin 11 | RESET — Reset input |
| Pin 12 | RC — PWM oscillator RC |
| Pin 13 | SENSE — Current sense input |
| Pin 14 | REF — Reference voltage |
| Pin 15 | FAULT — Fault output (open drain) |
| Pin 16 | OUTA_H — Phase A high-side gate drive |
| Pin 17 | OUTA_L — Phase A low-side gate drive |
| Pin 18 | OUTB_H — Phase B high-side gate drive |
| Pin 19 | OUTB_L — Phase B low-side gate drive |
| Pin 20 | OUTC_H — Phase C high-side gate drive |
| Pin 21 | OUTC_L — Phase C low-side gate drive |
| Pin 22 | GHA — Phase A high-side gate return |
| Pin 23 | GHB — Phase B high-side gate return |
| Pin 24 | GHC — Phase C high-side gate return |
| Pin 25 | CA — Bootstrap capacitor A |
| Pin 26 | CB — Bootstrap capacitor B |
| Pin 27 | CC — Bootstrap capacitor C |
| Pin 28 | SA — Phase A source (low-side return) |
| Pin 29 | SB — Phase B source (low-side return) |
| Pin 30 | SC — Phase C source (low-side return) |
| Pin 31 | VCP — Charge pump output |
| Pin 32 | VDD — Logic supply (5 V) |
| 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 | NC — Not connected (per datasheet) |
Typical Applications
A3938SLDTR-T is suitable for 6 applications: Industrial BLDC Servo Drives, E-Bike and Light-EV Traction Controllers, Three-Phase Pumps and Fans, CNC Spindle and Robotics Drives, 48V Telecom Auxiliary Systems, Drones and UAV Propulsion.
Industrial BLDC Servo Drives
The A3938SLDTR-T's 50 V motor supply ceiling and integrated synchronous rectification make it well-suited for industrial three-phase BLDC servo drives in the 24 V to 48 V class. The integrated bootstrap high-side supplies cut BOM by 6 to 8 discrete components per phase, while synchronous rectification reduces MOSFET body-diode losses by 20 to 40 percent at typical 10 to 20 kHz PWM rates. Designers typically place the A3938 between a 24 V or 48 V DC bus and an N-channel MOSFET bridge, with the controller logic running on a separate 3.3 V or 5 V MCU rail.
Recommended
E-Bike and Light-EV Traction Controllers
The A3938SLDTR-T's 50 V ceiling accommodates 36 V and 48 V battery platforms used in e-bikes, e-scooters, and light-EV traction controllers. Synchronous rectification improves battery range by an estimated 5 to 15 percent versus diode-only commutation by recovering energy normally lost to body-diode conduction. The TSSOP-38 footprint fits compact hub-motor housings, and the 18 V minimum motor rail handles deep-discharge cutoff. Pair with logic-level N-channel MOSFETs rated above peak phase current.
Recommended
Three-Phase Pumps and Fans
Three-phase BLDC pumps and high-performance fans benefit from the A3938SLDTR-T's integrated bootstrapped high-side drive, which eliminates 6 to 8 discrete components versus a discrete gate-driver design. The 50 V ceiling supports 24 V and 48 V fan/pump applications in telecom, server cooling, and HVAC. Synchronous rectification reduces switching losses enough to drop heatsink requirements in many designs. The TSSOP package and integrated protection make this a strong choice where PCB real estate is constrained.
Recommended
CNC Spindle and Robotics Drives
CNC spindle motors, robotic actuators, and small industrial automation axes use 24 V to 48 V three-phase BLDC motors in the 100 W to 1 kW class. The A3938SLDTR-T's 50 V ceiling and integrated fault protection support the dynamic braking and over-current events typical of these applications. Adjustable dead time lets designers tune the shoot-through margin for the chosen MOSFET. Synchronous rectification reduces MOSFET thermal stress under repeated start-stop duty cycles typical of pick-and-place axes.
Recommended
48V Telecom Auxiliary Systems
Telecom and mild-hybrid 48 V auxiliary systems (cooling fans, small pumps, blower motors) operate right at the A3938SLDTR-T's 50 V motor supply ceiling, leaving little headroom for back-EMF transients. The integrated synchronous rectification cuts MOSFET losses enough that designers can use smaller MOSFETs than a diode-only design. The TSSOP-38 footprint is well-supported in 48V telecom auxiliary designs where PCB area is at a premium but reliability must meet carrier-grade targets.
Recommended
Drones and UAV Propulsion
Multi-rotor drone propulsion in the 6S to 12S Li-Po class (22 V to 44 V) sits inside the A3938SLDTR-T's 18 V to 50 V motor supply window, with synchronous rectification delivering the high efficiency required for flight time. The TSSOP package is light and small, suiting compact ESC (electronic speed controller) boards. Adjustable dead time lets ESC designers optimize for the high PWM rates (often 24 to 48 kHz) used to keep propeller noise outside the human audible band.
Recommended
Recommended Products Summary
Engineering reference data for A3938SLDTR-T — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | A3938SLD-T | A3938SLD | A4985SLDTR-T | L6234 | L6398 |
|---|---|---|---|---|---|---|
| Brand | Allegro MicroSystems | Allegro MicroSystems | Allegro MicroSystems | Allegro MicroSystems | STMicroelectronics | STMicroelectronics |
| Package | 38-TSSOP (LD) | 38-TSSOP (LD) - same | 38-TSSOP (LD) - same | 38-TSSOP - same family | 38-TSSOP - same | 38-TSSOP - same |
| Motor Supply Voltage | 18 V to 50 V | 18 V to 50 V | 18 V to 50 V | 18 V to 50 V | 7 V to 52 V | Up to 600 V (gate driver, not motor supply) |
| Synchronous Rectification | Yes (low-side) | Yes | Yes | Yes | Yes | Yes |
| Adjustable Dead Time | Yes (external resistor) | Yes | Yes | Yes | Internal fixed | Internal fixed |
| Bootstrap Diodes | Integrated | Integrated | Integrated | Integrated | External required | External required |
| Topology | Three-phase BLDC pre-driver | Three-phase BLDC | Three-phase BLDC | Stepper / 3-phase | Three-phase BLDC | Three-phase gate driver (600V) |
| Operating Temperature | -20C to +85C | -20C to +85C | -20C to +85C | -20C to +85C | -40C to +150C (automotive capable) | -40C to +125C |
| Approx. Unit Price (1k qty) | USD 4.05 | USD 4.05 (tube) | USD 4.05 | USD 3.80 | USD 4.50 | USD 5.20 |
Key Differentiators
- Integrated bootstrap diodes (vs L6234)
- Adjustable dead time for shoot-through protection (vs L6398)
- 50 V ceiling tuned for 36 V and 48 V battery platforms (vs L6398)
Design Notes
Estimated: the A3938SLDTR-T itself only consumes the power needed to charge MOSFET gates, which is typically 0.2 to 0.5 W at 20 kHz switching. Thermal rise is dominated by the external MOSFETs. The TSSOP-38 package has a theta_JA around 80 C/W on a 1 sq inch copper pour; derate ambient to under 60 C for industrial designs, or attach a small copper heatsink tab to the TSSOP thermal pad if available. Always verify with the actual MOSFET gate charge Qg and switching frequency fSW, since gate drive loss per phase is approximately Qg * VDRV * fSW.
Place the three bootstrap capacitors (CA, CB, CC) as close as possible to the A3938SLDTR-T bootstrap pins to keep the high-side supply ripple below 0.5 V at full switching frequency. Use 0.1 microfarad to 1 microfarat X7R ceramics. Keep the SENSE resistor Kelvin-connected to the SA/SB/SC pins and the GND pin to avoid ground-bounce errors. Reserve a 4 mm keep-out around the high-side gate traces to prevent dv/dt coupling into logic traces.
Do not operate above 50 V motor supply or below 18 V - the A3938 will not start the charge pump and the high-side gate drive will collapse. Ensure dead time is set per the MOSFET turn-off delay at the worst-case hot junction; a dead time shorter than tD(off) causes shoot-through and immediate MOSFET failure. Do not leave the DT pin floating - the datasheet requires an external resistor for predictable dead time. Avoid running the SENSE pin without a current-limit resistor; sustained overcurrent will trigger the fault latch and require a reset cycle.
Compliance Information
RoHS and REACH compliant per Alldatasheet listing. The standard A3938SLDTR-T is not AEC-Q100 qualified; for automotive applications consult Allegro's automotive-grade BLDC drivers.
