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Allegro MicroSystems A3938SLQ
- Part No.:
- A3938SLQ
- Manufacturer:
- Allegro MicroSystems
- Category:
- Motor Drivers, Controllers
- Package:
- 36-BSOP (0.295", 7.50mm Width)
- Datasheet:
-
A3938SLQ.pdf
- Description:
- IC MOTOR DRIVER 18V-50V 36QSOP
- Quantity:
- Payment:
- Shipping:
Inventory:4,191
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Product details
Overview
A3938SLQ 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, synchronous rectification, and thermal/short-to-ground/fault diagnostics - used in industrial BLDC fans, power tools, and automated HVAC actuators.
For engineers reviewing the A3938SLQ datasheet, A3938SLQ pinout, A3938SLQ application, or A3938SLQ equivalent, key selection considerations include its 38-pin TSSOP-LD package, adjustable dead time via DEAD pin, peak current limit set by REF/SENSE, fast/slow decay mode selection via MODE pin, and bootstrap-capacitor–based high-side drive architecture.
Technical Context
The A3938SLQ implements Hall-input–driven commutation logic for 120°-spaced sensors, with internal pull-ups to LCAP (5 V) on H1/H2/H3 pins. Its gate drive architecture uses bootstrapped high-side drivers (GHA/GHB/GHC) and low-side outputs (GLA/GLB/GLC), each supporting external gate resistors for di/dt control.
Current regulation relies on a fixed off-time PWM circuit triggered by SENSE voltage exceeding REF-set threshold (ITRIP = VREF / RSENSE), with blanking time set by RC network. Protection includes VREG undervoltage lockout (9.1–10.2 V), thermal shutdown at 165°C, motor lead short-to-ground detection (>2 V drain-source differential), and fault latching cleared only on RESET toggle or power cycle.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Motor Supply Voltage | Up to 50 V - enables direct interface with 12–48 V industrial BLDC systems without external step-up. |
| Logic Regulator Output | LCAP = 4.75–5.25 V @ –3 mA - powers internal logic and provides reference for Hall inputs and FAULT/DEAD pins. |
| Gate Drive Capability | GHA/GHB/GHC: 10.4–12.8 V high-side output; GLA/GLB/GLC: VREG – 0.5 V low-side output - drives standard N-channel MOSFETs without level shifters. |
| Current Limit Accuracy | ±5 mV input offset at SENSE - ensures precise trip point setting for ITRIP = VREF / RSENSE across temperature. |
| Dead Time Range | 100 ns to 5.5 µs via DEAD–LCAP resistor - prevents cross-conduction during high-side/low-side switching transitions. |
| Thermal Shutdown | 165°C junction temperature with 10°C hysteresis - disables outputs and asserts FAULT to prevent MOSFET destruction under overload. |
| Fault Diagnostics | Open-drain FAULT pin signals invalid Hall code (000/111), VREG UVLO, thermal shutdown, or SA/SB/SC short-to-ground - enables system-level error recovery. |
Pinout & Package
Package: 38-pin TSSOP-LD (lead-free, 100% matte tin plating), 9.7 mm × 4.4 mm footprint, 1.2 mm max height, JEDEC MO-153 compliant.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SA/SB/SC | Motor phase terminals & bootstrap capacitor return | Direct connection to motor windings; also serve as negative rails for CA/CB/CC bootstrap supplies - requires low-inductance PCB routing. |
| GHA/GHB/GHC | High-side N-MOSFET gate drivers | Provide boosted gate voltage (≈VREG + VSx) to turn on external high-side N-channel MOSFETs - require external series gate resistors for dv/dt control. |
| GLA/GLB/GLC | Low-side N-MOSFET gate drivers | Drive low-side MOSFET gates referenced to PGND - support synchronous rectification during PWM off-cycle. |
| H1/H2/H3 | Hall sensor inputs | 120°-spaced commutation inputs with internal 50 kΩ pull-ups to LCAP - tolerate TTL/CMOS logic levels; noisy environments need external filtering. |
| REF/SENSE | Current limit comparator inputs | REF sets peak current threshold; SENSE monitors shunt voltage - blanked for tBLANK after PWM edge to reject switching transients. |
| RC | Fixed off-time timing node | RT–CT network sets tOFF ≈ RT × CT (10–50 µs); same CT sets blank time - critical for stable current regulation and audible noise suppression. |
| DEAD | Dead time adjustment | Resistor to LCAP sets delay between high-side turn-off and low-side turn-on - prevents shoot-through in external power stage. |
| FAULT | Open-drain fault indicator | Pulled high externally (e.g., 5.1 kΩ) - asserts low on any fault condition except short-to-ground, which auto-clears per commutation. |
Key Features
| Feature | Design Value |
|---|---|
| Synchronous rectification | Enables low-side-only conduction during PWM off-cycle - reduces MOSFET conduction loss vs. body-diode freewheeling and eliminates need for external clamp diodes. |
| Adjustable decay mode | MODE pin selects fast decay (both FETs off) or slow decay (high-side off only) - allows tuning of torque ripple and acoustic noise in motor control loops. |
| Power-loss braking | BRKCAP + BRKSEL enable dynamic braking using reservoir capacitor during VREG undervoltage or RESET assertion - maintains controlled stop even during main supply failure. |
| Integrated protection suite | Covers bootstrap charge monitoring, VREG UVLO, thermal shutdown, Hall invalid code detection, and motor lead short-to-ground - reduces external fault-handling circuitry. |
| Internal 5 V regulator (LCAP) | Supplies Hall sensors, logic, and FAULT/DEAD bias - eliminates need for external LDO while maintaining stable reference under load transients. |
Applications
| Industrial BLDC Fans | Power Tool Motor Controllers |
|---|---|
|
Use Scenario: High-reliability cooling in PLC cabinets and servo drive enclosures requiring continuous operation at 40–60°C ambient. IC Role / Device Role / Timing Role: Three-phase commutation controller with Hall feedback, current-regulated PWM, and thermal fault shutdown - manages motor speed/torque while protecting against stalled-rotor overcurrent. Use Value: Synchronous rectification cuts MOSFET conduction loss by ~30% vs. diode-based designs, reducing heatsink size and enabling fan speeds up to 12,000 RPM at 48 V. |
Use Scenario: Cordless drill/driver with variable-speed trigger and electronic brake for rapid stop on release. IC Role / Device Role / Timing Role: Gate driver and current limiter interfacing microcontroller PWM and Hall sensors - executes commutation sequence, enforces peak current limit, and triggers dynamic brake on BRAKE pin assertion. Use Value: Power-loss braking via BRKCAP sustains full brake torque for >300 ms after battery disconnect, meeting IEC 62841-1 safety requirements for tool stop time. |
| Automated HVAC Dampers | Medical Infusion Pumps |
|
Use Scenario: Precision airflow control in hospital HVAC systems where position accuracy and silent operation are critical. IC Role / Device Role / Timing Role: Low-noise BLDC driver with selectable decay mode and fixed off-time current control - regulates motor current to achieve smooth, jitter-free damper actuation. Use Value: Adjustable dead time (100 ns–5.5 µs) and RC-timed blanking suppress EMI from gate switching, enabling compliance with CISPR 11 Class B emissions limits. |
Use Scenario: Peristaltic pump in portable infusion devices requiring fail-safe motor stop during power interruption or occlusion. IC Role / Device Role / Timing Role: Fault-aware motor controller with short-to-ground detection on SA/SB/SC and latched thermal shutdown - halts motor and asserts FAULT on tubing blockage or motor stall. Use Value: Short-to-ground protection clears automatically each commutation, allowing recovery from transient faults without MCU intervention - improves pump uptime and reduces false alarms. |
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 decoding logic required - but lacks synchronous rectification and power-loss braking. | Best for closed-loop field-oriented control (FOC) with encoder feedback; less suitable for Hall-only open-loop systems needing minimal BOM cost. | Choose STSPIN32F0A when firmware-based commutation and real-time torque control are needed; A3938SLQ remains preferred for deterministic Hall-based timing and analog current limiting. |
| TB9051FTG | Automotive-grade 3-phase pre-driver with CAN interface and built-in watchdog; higher VBB rating (60 V) but requires external 5 V LDO for logic supply. | Targeted at automotive HVAC and EPS; includes ASIL-B functional safety features absent in A3938SLQ. | Select TB9051FTG for ISO 26262-compliant designs; A3938SLQ offers lower system cost and simpler layout for industrial equipment not requiring automotive qualification. |
Compared with STSPIN32F0A and TB9051FTG, the A3938SLQ delivers deterministic Hall-based commutation with analog current limiting, integrated synchronous rectification, and power-loss braking - making it optimal for cost-sensitive, high-reliability industrial BLDC systems where MCU overhead and automotive certification are unnecessary.
Availability
A3938SLQ is available at Aetrix Electronics and suitable for industrial BLDC fans, power tool motor controllers, automated HVAC dampers, and medical infusion pumps requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for A3938SLQ 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 ICs, specializing in motion control, current sensing, and motor driver solutions for industrial, automotive, and consumer markets.
The A3938SLQ belongs to Allegro's three-phase BLDC controller product line, engineered for robust Hall-sensor–based commutation, efficient N-channel MOSFET driving, and comprehensive fault protection in demanding industrial environments.
FAQ
What is the maximum motor supply voltage supported by the A3938SLQ?
The A3938SLQ supports a maximum motor supply voltage (VBB) of 50 V, as specified in its Absolute Maximum Ratings table. This allows direct integration into 48 V industrial systems without external voltage translation. Operation above this limit risks permanent damage to internal high-side drivers and bootstrap circuitry. For 12 V applications, VBB must be shorted to VREG while ensuring VREG stays within its 15 V absolute maximum rating.
How does the A3938SLQ implement current limiting, and what components set the trip threshold?
The A3938SLQ uses an internal fixed off-time PWM current-control circuit where the peak load current is determined by ITRIP = VREF / RSENSE. The REF pin accepts an external voltage (typically from a DAC or resistor divider), and the SENSE pin monitors voltage across a shunt resistor placed between motor phase and PGND. The device blanks the SENSE comparator for tBLANK after each PWM edge to reject switching noise, ensuring accurate current regulation.
Does the A3938SLQ support both fast and slow current decay modes, and how is this selected?
Yes, the A3938SLQ supports both fast and slow decay modes via the MODE pin. When MODE = 0, fast decay occurs: high-side and low-side FETs turn off simultaneously during PWM off-time, forcing current recirculation through freewheeling paths. When MODE = 1, slow decay occurs: only the high-side FET turns off, allowing low-side conduction - reducing torque ripple and audible noise. Internal 50 kΩ pull-up to LCAP defaults MODE to slow decay if left unconnected.
What protection features are integrated into the A3938SLQ, and how are faults reported?
The A3938SLQ integrates bootstrap charge monitoring, VREG undervoltage lockout (9.1–10.2 V), thermal shutdown at 165°C, Hall sensor invalid code detection (000/111), and motor lead short-to-ground protection. All faults assert the open-drain FAULT pin low. Only short-to-ground is auto-cleared at each commutation; other faults require RESET pin toggle or power cycle to recover. FAULT status can be monitored by an external pull-up resistor (e.g., 5.1 kΩ).
Can the A3938SLQ perform dynamic braking, and what pins control this function?
Yes, the A3938SLQ supports dynamic braking via the BRAKE pin: asserting BRAKE = 1 turns on all low-side FETs and turns off all high-side FETs, shorting motor back-EMF to stop rotation rapidly. Braking behavior on power loss or RESET is controlled by BRKSEL and BRKCAP: BRKSEL selects coast (0) or brake (1) mode, while BRKCAP connects a reservoir capacitor (e.g., 4.7 µF) to sustain gate drive during supply dropout - enabling reliable braking even after main power fails.
A3938SLQ Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Allegro MicroSystems
- Series:
- -
- Package/Case:
- 36-BSOP (0.295", 7.50mm 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:
- 36-QSOP
A3938SLQ FAQ
1.How can I place an order for A3938SLQ through Aetrix?
Please submit a Request for Quotation (RFQ) for A3938SLQ 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 A3938SLQ reliable?
The price and inventory of A3938SLQ are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A3938SLQ is usually 5 days.
3.What payment methods are accepted for A3938SLQ?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A3938SLQ transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A3938SLQ?
A3938SLQ orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A3938SLQ 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 A3938SLQ?
For technical support, including A3938SLQ datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A3938SLQ requirements.
6.How does Aetrix verify that A3938SLQ is sourced from the original manufacturer or authorized distributors?
All A3938SLQ 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 A3938SLQ meets industry standards.
7.What is the process for return or replacement of A3938SLQ?
All A3938SLQ units undergo pre-shipment inspection (PSI). If there is an issue with A3938SLQ, 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 A3938SLQ part is unused and in its original packaging.
Return procedure for A3938SLQ:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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