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Allegro MicroSystems A3938SLD-T
- Part No.:
- A3938SLD-T
- Manufacturer:
- Allegro MicroSystems
- Category:
- Motor Drivers, Controllers
- Package:
- 38-TFSOP (0.173", 4.40mm Width)
- Datasheet:
-
A3938SLD-T.pdf
- Description:
- IC MOTOR DRIVER 18V-50V 38TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:3,846
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Product details
Overview
A3938SLD-T from Allegro MicroSystems is a three-phase brushless DC motor controller IC with integrated high-current N-channel MOSFET gate drivers, 50 V motor supply capability, internal 5 V logic regulator (LCAP), and fixed off-time PWM current control. It supports Hall sensor–based 120° commutation and delivers synchronous rectification for reduced MOSFET power loss in industrial BLDC drives.
For engineers reviewing the A3938SLD-T datasheet, A3938SLD-T pinout, A3938SLD-T application, or A3938SLD-T equivalent, key selection criteria include its 38-pin TSSOP-LD package, adjustable dead time via DEAD pin, dual decay mode (fast/slow) selection via MODE pin, and fault diagnostics including short-to-ground detection on SA/SB/SC motor leads.
Technical Context
The A3938SLD-T implements Hall-input–driven six-step commutation logic for 120° spaced sensors, with DIR pin polarity reversal and BRAKE/RESET-controlled coasting or dynamic braking. Its internal fixed off-time PWM current regulator uses external RC network on RC pin to set tOFF (10–50 µs), while REF and SENSE pins define peak current via ITRIP = VREF/RSENSE.
Protection architecture includes bootstrap capacitor charge monitoring (ICX threshold ≈ –9 mA), VREG undervoltage lockout (9.1–9.7 V trip), thermal shutdown at 165°C with 10°C hysteresis, and latched short-to-ground detection on motor phases-cleared per commutation cycle. Synchronous rectification engages low-side FETs only during PWM off-cycle recirculation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Motor Supply Voltage | Up to 50 V - supports wide-range BLDC motors without external step-down regulation. |
| Gate Drive Outputs | 6-channel (GHA/GHB/GHC/GLA/GLB/GLC) - drives external N-channel power MOSFETs with 11.6 V typical high-side drive voltage. |
| Current Regulation | Fixed off-time PWM with user-settable ITRIP - enables precise torque limiting using REF voltage and external sense resistor. |
| Thermal Shutdown | 165°C junction temperature with 10°C hysteresis - prevents latch-up and ensures safe recovery before restart. |
| Package | 38-pin TSSOP-LD (lead-free, matte tin plating) - 9.7 mm × 4.4 mm footprint with 51°C/W θJA on 4-layer JEDEC PCB. |
| Fault Diagnostics | Open-drain FAULT output - signals invalid Hall code, VREG UVLO, thermal shutdown, or motor lead short-to-ground. |
| Logic Supply | Internal 5 V regulator (LCAP) - powers internal logic and provides reference for pull-ups on H1/H2/H3, DIR, MODE, etc. |
Pinout & Package
38-pin TSSOP-LD package (JEDEC MO-153 BD-1 compliant), lead-free with 100% matte tin plated leadframe. Exposed pad not specified; thermal resistance RθJA = 51°C/W on standard 4-layer PCB.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SA/SB/SC | Motor phase terminals & bootstrap capacitor return | Direct connection to motor windings; also serve as negative reference for CA/CB/CC bootstrap supplies. |
| GHA/GHB/GHC | High-side gate drive outputs | Drive N-channel high-side MOSFET gates; require external series resistors to control dv/dt and prevent cross-conduction. |
| GLA/GLB/GLC | Low-side gate drive outputs | Drive N-channel low-side MOSFET gates; enable synchronous rectification during PWM off-cycle. |
| H1/H2/H3 | Hall sensor inputs | 120° electrical spacing support; internally pulled up to LCAP (5 V) via 50 kΩ resistors. |
| REF/SENSE | Current limit comparator inputs | Set peak winding current: ITRIP = VREF/RSENSE; SENSE blanked for tBLANK ≈ 0.91 µs after PWM edge. |
| DEAD | Dead time adjustment input | Resistor to LCAP sets delay (100 ns–5.5 µs) between high-side and low-side turn-off/on to prevent shoot-through. |
| FAULT | Open-drain fault indicator | Pulled high externally (e.g., 5.1 kΩ) to signal any active fault condition; requires external pull-up for operation. |
| VREG | 13 V regulated supply | Provides gate drive bias and bootstrap charging current; requires ≥10 µF low-ESR capacitor to AGND. |
| LCAP | 5 V logic reference | Internal regulator output powering logic and pull-ups; decoupled with 0.1 µF ceramic capacitor to AGND. |
| PGND/AGND | Power and analog ground returns | PGND carries high-current gate drive return; AGND is low-noise analog reference - must be separated and joined at single point. |
Key Features
| Feature | Design Value |
|---|---|
| Synchronous rectification | Enables low-side FET conduction only during PWM off-cycle, eliminating body diode losses and removing need for external clamp diodes. |
| Adjustable dead time | Configurable 100 ns–5.5 µs delay via DEAD pin resistor - prevents cross-conduction across all operating conditions and MOSFET types. |
| Dual decay mode | MODE pin selects fast decay (both FETs off) or slow decay (high-side off only) - optimizes current ripple, torque smoothness, and acoustic noise. |
| Power-loss braking | BRKCAP + BRKSEL enable controlled dynamic brake during VREG undervoltage or RESET assertion - maintains braking even after main supply collapse. |
| Hall-input fault protection | Rejects illegal codes (000/111) and triggers FAULT + coast - prevents erratic commutation due to noisy or misaligned Hall sensors. |
| Integrated bootstrap monitor | Disables high-side turn-on until bootstrap capacitor charge current falls below –9 mA - ensures reliable high-side gate drive voltage. |
Applications
| Industrial Fan Control | Automotive HVAC Blower |
|---|---|
|
Use Scenario: Variable-speed centrifugal fan in factory ventilation system requiring EMI-optimized commutation and thermal resilience. IC Role / Device Role / Timing Role: Three-phase BLDC controller managing Hall-based commutation, current-regulated torque, and fault-safe shutdown. Use Value: Synchronous rectification reduces MOSFET conduction loss by >30% vs. diode-based recirculation, lowering heatsink requirements in enclosed enclosures. |
Use Scenario: Cabin air blower in passenger vehicle with strict EMC and functional safety constraints. IC Role / Device Role / Timing Role: Motor controller providing diagnostic FAULT output, short-to-ground detection, and VREG UVLO for ASIL-B–aligned subsystem monitoring. Use Value: Latched short-to-ground fault cleared per commutation cycle enables rapid stall recovery without full reset - critical for occupant comfort continuity. |
| Medical Infusion Pump Drive | Robot Joint Actuator |
|
Use Scenario: Precision peristaltic pump requiring silent, low-vibration motor control and fail-safe stop behavior. IC Role / Device Role / Timing Role: Current-regulated BLDC driver with adjustable fixed off-time (RC network) and dynamic brake (BRAKE pin) for immediate rotor hold. Use Value: Fast/slow decay mode selection minimizes audible PWM noise at low speeds - essential for quiet clinical environments. |
Use Scenario: Torque-controlled elbow/knee joint in collaborative robot needing responsive current limiting and thermal margin. IC Role / Device Role / Timing Role: Gate driver IC delivering 13 V VREG supply, 165°C thermal shutdown, and real-time ITRIP adjustment via REF voltage. Use Value: Internal 5 V LCAP regulator powers Hall sensor pull-ups and logic - eliminates need for external LDO, reducing BOM count and layout area. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar three-phase BLDC motor controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| STSPIN32F0A | Integrated 32-bit ARM Cortex-M0 MCU + gate drivers; no external Hall interface required; supports sensorless FOC. | Best for designs needing closed-loop field-oriented control, firmware customization, or compact integration - not drop-in replacement. | Select when replacing legacy Hall-based systems with sensorless or programmable control; requires full firmware redesign. |
| TMC6300-LA | Three-phase gate driver with integrated shunt amplifiers and SPI-configurable current regulation; no internal Hall logic. | Requires external microcontroller for commutation sequencing; better suited for custom FOC or trapezoidal algorithms with digital tuning. | Choose for high-precision current sensing and flexible decay control where Hall decoding is handled externally. |
Compared with STSPIN32F0A and TMC6300-LA, the A3938SLD-T offers dedicated Hall-input hardware logic, fixed off-time analog current regulation, and minimal external component count - making it optimal for cost-sensitive, high-volume BLDC systems where deterministic timing and analog simplicity are prioritized over programmability.
Availability
A3938SLD-T is available at Aetrix Electronics and suitable for industrial fan control, automotive HVAC blowers, medical infusion pumps, and robotic joint actuators requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for A3938SLD-T includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Allegro MicroSystems is a U.S.-based designer of high-performance magnetic sensing and power IC solutions, specializing in motion control, current sensing, and motor driver technologies since 1989.
The A3938SLD-T belongs to Allegro's three-phase BLDC gate driver product line, engineered for robust Hall-sensor–based motor control in demanding industrial and automotive environments where reliability, thermal resilience, and analog precision are critical.
FAQ
What is the maximum motor supply voltage supported by the A3938SLD-T?
The A3938SLD-T supports a maximum load supply voltage (VBB) of 50 V, as specified in its Absolute Maximum Ratings table. This allows direct interface with common 24 V and 48 V BLDC motor systems without intermediate voltage conversion. Operation above 50 V risks permanent damage; for 12 V applications, VBB must be shorted to VREG while maintaining VREG ≤ 15 V to avoid overstress.
How does the A3938SLD-T implement current limiting?
The A3938SLD-T uses internal fixed off-time PWM current control. Peak winding current is set by ITRIP = VREF/RSENSE, where VREF is applied to the REF pin and RSENSE is the external current-sense resistor connected to SENSE. When sensed voltage exceeds VREF, the comparator disables the source driver for a user-defined off-time determined by the RC network on the RC pin.
Can the A3938SLD-T drive both high-side and low-side N-channel MOSFETs without external level shifters?
Yes - the A3938SLD-T integrates a bootstrapped high-side driver architecture. Each high-side output (GHA/GHB/GHC) is supplied via its dedicated bootstrap capacitor (CA/CB/CC), enabling full N-channel FET use without external level-shifting circuitry. The internal charge pump and bootstrap monitor ensure reliable gate drive voltage (typically 11.6 V) as long as the bootstrap capacitors are properly sized and charged during low-side conduction.
What fault conditions trigger the open-drain FAULT output on the A3938SLD-T?
The FAULT pin asserts low (open-drain active-low) for five confirmed conditions: invalid Hall sensor code (000 or 111), VREG undervoltage (below 9.1 V), junction temperature exceeding 165°C, motor lead short-to-ground (detected as >2 V between VBB and SA/SB/SC), or bootstrap capacitor undercharge (ICX < –9 mA). Only the short-to-ground fault is latched and cleared automatically at each commutation step.
Is the A3938SLD-T pin-compatible with other Allegro BLDC controllers like the A4964 or A3977?
No - the A3938SLD-T is not pin-compatible with the A4964 or A3977. It uses a unique 38-pin TSSOP-LD footprint with distinct pin assignments (e.g., dedicated LCAP, DEAD, BRKCAP, and BRKSEL pins absent in earlier generations). Migration requires PCB layout revision and firmware adaptation due to differences in Hall logic implementation, decay control, and protection signaling.
A3938SLD-T Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Allegro MicroSystems
- Series:
- -
- Package/Case:
- 38-TFSOP (0.173", 4.40mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Motor Type - Stepper:
- -
- Motor Type - AC, DC:
- Brushless DC (BLDC)
- Function:
- Controller - Commutation, Direction Management
- Output Configuration:
- Pre-Driver - Half Bridge (3)
- Interface:
- Parallel, PWM
- Technology:
- Power MOSFET
- Step Resolution:
- -
- Applications:
- General Purpose
- Current - Output:
- -
- Voltage - Supply:
- 18V ~ 50V
- Voltage - Load:
- -
- Operating Temperature:
- -20°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 38-TSSOP
A3938SLD-T FAQ
1.How can I place an order for A3938SLD-T through Aetrix?
Please submit a Request for Quotation (RFQ) for A3938SLD-T on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for A3938SLD-T reliable?
The price and inventory of A3938SLD-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A3938SLD-T is usually 5 days.
3.What payment methods are accepted for A3938SLD-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A3938SLD-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A3938SLD-T?
A3938SLD-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A3938SLD-T order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for A3938SLD-T?
For technical support, including A3938SLD-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A3938SLD-T requirements.
6.How does Aetrix verify that A3938SLD-T is sourced from the original manufacturer or authorized distributors?
All A3938SLD-T products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that A3938SLD-T meets industry standards.
7.What is the process for return or replacement of A3938SLD-T?
All A3938SLD-T units undergo pre-shipment inspection (PSI). If there is an issue with A3938SLD-T, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The A3938SLD-T part is unused and in its original packaging.
Return procedure for A3938SLD-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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