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Allegro MicroSystems A8447SLJTR-T
- Part No.:
- A8447SLJTR-T
- Manufacturer:
- Allegro MicroSystems
- Package:
- 8-SOIC (0.154", 3.90mm Width) Exposed Pad
- Datasheet:
-
A8447SLJTR-T.pdf
- Description:
- IC REG BUCK ADJ 3A 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,051
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Product details
Overview
A8447SLJTR-T from Allegro MicroSystems is a discontinued 3 A, high-efficiency, fixed off-time current-mode buck regulator supporting 8–50 V input and adjustable 0.8–24 V output. It integrates a 450 mΩ (typ.) DMOS switch, uses external diode/inductor/filter, and delivers up to 90% efficiency at 3 A load in typical 3.3 V applications such as industrial power supplies and POS equipment.
For engineers reviewing the A8447SLJTR-T datasheet, A8447SLJTR-T pinout, A8447SLJTR-T application, or A8447SLJTR-T equivalent, key selection considerations include its SOIC-8 LJ package with exposed thermal pad, 0.8 V ±2% feedback reference, 200 ns internal blanking for diode reverse-recovery noise immunity, and discontinuous/continuous conduction mode operation across light-to-full load.
Technical Context
The A8447SLJTR-T implements fixed off-time current-mode control with external RTSET resistor programming (7.65–105 kΩ), enabling switching frequencies from ~100 kHz to >200 kHz depending on VIN/VOUT ratio. Its internal blanking circuit suppresses transients from external Schottky diode recovery, with 200 ns nominal blanking time.
It features dual overcurrent protection: 3.5 A (min) peak limit under normal operation and 1.5 A (typ.) short-circuit limit when FB falls below 0.4 V. Thermal shutdown activates at 165°C with 15°C hysteresis, and soft-start ramps output over 10 ms (typ.) with 3.5 A current limit enabled.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 8–50 V - supports wide industrial bus voltages including 24 V and 36 V systems without pre-regulation |
| Output Current | 3 A continuous - limited by thermal design and PCB copper area; derates above 85°C ambient |
| Feedback Reference | 0.8 V ±2% - sets output voltage via resistor divider (VOUT = 0.8 × (1 + R1/R2)) with <±3% regulation error |
| Switch RDS(on) | 450 mΩ (typ. at 25°C) - determines conduction loss and junction temperature rise under full load |
| Quiescent Current | 0.9–1.35 mA (VIN = 42 V, VBIAS = VOUT) - enables low-noise biasing from regulated output to improve system efficiency |
| UVLO Threshold | 6.9 V (typ.) with 1 V hysteresis - prevents erratic startup during brown-out conditions on high-voltage rails |
| Thermal Shutdown | 165°C (typ.) with 15°C hysteresis - protects die during overload or poor heatsinking; auto-restarts after cooldown |
Pinout & Package
Package: 8-pin SOIC with exposed thermal pad (LJ suffix), 4-layer PCB thermal resistance RθJA = 35°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - BOOT | Gate drive boost node | Charges bootstrap capacitor to enable high-side NMOS gate drive; requires 0.01 µF ceramic capacitor to LX |
| 2 - ENB | Enable logic input | Active-low control: pulled to GND to enable soft-start; open-circuit disables output and discharges VOUT |
| 3 - TSET | Off-time setting | Resistor to GND sets fixed off-time (7–200 µs); minimum 7.65 kΩ required to avoid violating minimum on-time |
| 4 - GND | Power and signal ground | Star-ground connection point; must tie exposed thermal pad directly to large copper pour via thermal vias |
| 5 - FB | Feedback input | Senses output voltage divider; high-impedance node (±100 nA bias) requiring short trace and low-noise layout |
| 6 - VBIAS | Bias supply input | Connected to VOUT when target is 3.3–5 V for efficiency; otherwise powered from VIN with higher quiescent current |
| 7 - LX | Switching node | Connects to inductor and cathode of external Schottky diode; high dv/dt node requiring tight layout and EMI mitigation |
| 8 - VIN | Main supply input | Accepts 8–50 V; requires local 0.22 µF ceramic + bulk electrolytic (e.g., 100 µF/50 V) placed adjacent to pin |
Key Features
| Feature | Design Value |
|---|---|
| Wide input range (8–50 V) | Eliminates need for pre-regulators in 24 V/36 V industrial and POS systems; compatible with automotive battery transients |
| Integrated 450 mΩ DMOS switch | Reduces BOM count and layout complexity vs. controller-only solutions; enables compact 3 A buck designs |
| Adjustable output (0.8–24 V) | Supports diverse rail requirements (e.g., 1.5 V, 1.8 V, 3.3 V, 5 V, 12 V) using only two external resistors |
| Internal 200 ns blanking circuit | Suppresses false triggering from Schottky diode reverse recovery spikes, improving stability without snubbers |
| SOIC-8 LJ with exposed thermal pad | Enables >2 W power dissipation on standard 4-layer PCBs; thermal vias to inner ground plane reduce θJA to 35°C/W |
Applications
| Printer Power Supplies | POS Terminal Power |
|---|---|
|
Use Scenario: Provides stable 3.3 V or 5 V rail for thermal print head drivers and microcontroller in compact receipt printers. IC Role / Device Role / Timing Role: Primary DC-DC step-down regulator converting 24 V bus to logic-level rails. Use Value: High efficiency (>88% at 2 A) minimizes heat in sealed enclosures; cycle-skipping maintains regulation down to 10 mA load. |
Use Scenario: Powers embedded ARM processor, display, and USB peripherals in point-of-sale terminals operating from 24 V industrial supply. IC Role / Device Role / Timing Role: Adjustable buck converter delivering 1.8 V core and 3.3 V I/O rails with independent feedback networks. Use Value: 0.8 V reference tolerance (±2%) ensures accurate voltage setting; UVLO prevents malfunction during 24 V brownouts. |
| Industrial Control Modules | Tape Drive Power |
|
Use Scenario: Generates 12 V auxiliary rail for solenoid drivers and sensor interfaces in programmable logic controllers (PLCs). IC Role / Device Role / Timing Role: High-voltage buck regulator accepting 36 V nominal input with robust 50 V absolute max rating. Use Value: Integrated thermal shutdown (165°C) and cycle-skipping light-load operation ensure reliability in unventilated cabinets. |
Use Scenario: Supplies regulated 5 V to tape transport motor drivers and servo amplifiers in enterprise backup systems. IC Role / Device Role / Timing Role: Fixed off-time current-mode controller with external diode enabling fast transient response to motor start pulses. Use Value: 3.5 A peak current limit handles motor inrush; blanking circuit rejects diode recovery noise during direction reversals. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar high-voltage buck regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| A8498 | Successor device with improved efficiency (up to 93%), lower RDS(on) (320 mΩ), and integrated bootstrap diode; same SOIC-8 LJ package. | Designed for new designs requiring longer product lifecycle support; supports identical 8–50 V input and 0.8–24 V output range. | Select A8498 for new designs-Allegro explicitly recommends it as the replacement for A8447SLJTR-T in all new applications. |
| LM5118QMH/NOPB | Automotive-grade 100 V input buck controller (not integrated switch); requires external MOSFET, diode, and bootstrap circuit. | Targeted at AEC-Q100 automotive applications with extended temperature range (–40°C to 125°C) and fault reporting pins. | Choose LM5118QMH/NOPB only if 100 V input capability, automotive qualification, or design flexibility outweighs BOM simplicity. |
Compared with A8447SLJTR-T, the A8498 offers higher efficiency and longer-term availability but requires no PCB changes; the LM5118QMH/NOPB provides greater voltage headroom and automotive compliance at the cost of added components and layout complexity.
Availability
A8447SLJTR-T is available at Aetrix Electronics and suitable for industrial control modules, POS terminal power, and printer power supplies requiring stable component supply despite its discontinued status.
Supply support for A8447SLJTR-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 power ICs and magnetic sensors, headquartered in Worcester, Massachusetts.
The A8447 belongs to Allegro's high-voltage buck regulator product line, engineered for industrial, POS, and office automation applications demanding robust 8–50 V input operation and simple external component count.
FAQ
Is A8447SLJTR-T still in production?
No, A8447SLJTR-T is a discontinued product. Allegro ceased production effective December 1, 2015. It is not recommended for new designs, and samples are no longer available. Aetrix Electronics maintains legacy inventory for existing production continuity, but long-term supply cannot be guaranteed beyond current stock levels.
What is the recommended replacement for A8447SLJTR-T?
The officially recommended replacement is the A8498, which shares the same SOIC-8 LJ package, 8–50 V input range, and 0.8–24 V adjustable output. The A8498 improves on A8447SLJTR-T with lower RDS(on), higher efficiency, integrated bootstrap diode, and active product lifecycle support.
Can A8447SLJTR-T operate with input voltage below 8 V?
No. A8447SLJTR-T has a 6.9 V (typ.) undervoltage lockout threshold and is specified for operation only from 8 V to 50 V. Operation below 8 V will cause the device to disable output and may result in unstable regulation or failure to start.
What is the function of the TSET pin on A8447SLJTR-T?
The TSET pin on A8447SLJTR-T sets the fixed off-time via an external resistor to GND. Off-time ranges from ~7 µs to 200 µs depending on resistor value (7.65–105 kΩ) and VBIAS voltage. This directly determines switching frequency and affects light-load efficiency and ripple performance.
Does A8447SLJTR-T require an external Schottky diode?
Yes, A8447SLJTR-T requires an external Schottky diode (e.g., NSQ03A06) connected between LX and VOUT. The device does not integrate a synchronous rectifier; the diode provides the return path for inductor current during the off-time and must handle ≥1.2× the maximum load current.
A8447SLJTR-T Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Allegro MicroSystems
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width) Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Output Type:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 8V
- Voltage - Input (Max):
- 50V
- Voltage - Output (Min/Fixed):
- 0.8V
- Voltage - Output (Max):
- 24V
- Current - Output:
- 3A
- Frequency - Switching:
- -
- Synchronous Rectifier:
- No
- Operating Temperature:
- -20°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC-EP
A8447SLJTR-T FAQ
1.How can I place an order for A8447SLJTR-T through Aetrix?
Please submit a Request for Quotation (RFQ) for A8447SLJTR-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 A8447SLJTR-T reliable?
The price and inventory of A8447SLJTR-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A8447SLJTR-T is usually 5 days.
3.What payment methods are accepted for A8447SLJTR-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A8447SLJTR-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A8447SLJTR-T?
A8447SLJTR-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A8447SLJTR-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 A8447SLJTR-T?
For technical support, including A8447SLJTR-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A8447SLJTR-T requirements.
6.How does Aetrix verify that A8447SLJTR-T is sourced from the original manufacturer or authorized distributors?
All A8447SLJTR-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 A8447SLJTR-T meets industry standards.
7.What is the process for return or replacement of A8447SLJTR-T?
All A8447SLJTR-T units undergo pre-shipment inspection (PSI). If there is an issue with A8447SLJTR-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 A8447SLJTR-T part is unused and in its original packaging.
Return procedure for A8447SLJTR-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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