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Allegro MicroSystems A8499SLJTR-T
- Part No.:
- A8499SLJTR-T
- Manufacturer:
- Allegro MicroSystems
- Package:
- 8-SOIC (0.154", 3.90mm Width) Exposed Pad
- Datasheet:
-
A8499SLJTR-T.pdf
- Description:
- IC REG BUCK ADJ 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,852
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Product details
Overview
A8499SLJTR-T from Allegro MicroSystems is a high-voltage, fixed off-time, current-mode buck switching regulator in an 8-lead SOIC with exposed thermal pad (LJ package), supporting 8–50 V input and adjustable 1.2–24 V output up to 1.2 A continuous load, with integrated DMOS switch and internal soft-start for printer and consumer power supply applications.
For engineers reviewing the A8499SLJTR-T datasheet, A8499SLJTR-T pinout, A8499SLJTR-T application, or A8499SLJTR-T equivalent, this page delivers verified electrical parameters, thermal characteristics, functional block context, and discontinued-status-aware selection guidance for legacy design support and transition planning.
Technical Context
The A8499SLJTR-T implements fixed off-time control with external TSET resistor programming (e.g., 121 kΩ sets ~15 µs off-time), enabling operation across wide VIN/VOUT ratios while maintaining cycle-skipping regulation at light loads. Its current-mode architecture uses peak-current limiting (2.2–3 A) and internal blanking (200 ns) to suppress diode reverse-recovery noise.
Thermal management relies on the exposed pad in the LJ package (RθJA = 35°C/W on 4-layer PCB), with thermal shutdown at 165°C and 15°C hysteresis. Bias is supplied via VBIAS connected to VOUT (for 3.3–5 V outputs) or VIN, eliminating external bias supplies while maintaining efficiency.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 8–50 V - supports wide industrial and automotive input transients without external pre-regulation |
| Output Voltage Range | 1.2–24 V (adjustable via FB resistor divider) - enables single IC to serve multiple rail requirements |
| Continuous Output Current | 1.2 A - validated at 3.3 V/1.2 A with 47 µH inductor and 100 µF/50 V output capacitor |
| Feedback Reference Voltage | 1.200 V ±2% - sets output accuracy; VOUT = 1.2 × (1 + R1/R2) |
| Switch On-Resistance | 700–800 mΩ @ 25°C - determines conduction loss and thermal rise under full load |
| Soft Start Time | 10 ms nominal - limits inrush current into output capacitor during power-up |
| Thermal Shutdown Threshold | 165°C junction - protects against sustained overload or poor heatsinking |
Pinout & Package
Package: 8-lead SOIC with exposed thermal pad (suffix LJ), 4.90 × 3.90 mm body, 1.75 mm height, 0.65 mm lead pitch. Exposed pad must be soldered to PCB thermal plane with ≥4 thermal vias for RθJA ≤35°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BOOT | Gate drive bootstrap node | Charges high-side driver circuit; requires 0.01 µF ceramic capacitor to LX |
| ENB | Enable logic input | Pulled low to enable; open-circuit disables output and forces decay to 0 V |
| TSET | Fixed off-time programming | Resistor to GND sets tOFF (e.g., 121 kΩ → ~15 µs); critical for minimum on-time compliance |
| GND | Analog and power ground reference | Common return for FB, ENB, TSET, and thermal pad; must be low-impedance |
| FB | Feedback input | Senses output voltage divider; 100 nA bias current enables high-resistor-divider designs |
| VBIAS | Bias supply input | Connected to VOUT for 3.3–5 V outputs to improve efficiency; otherwise powered from VIN |
| LX | Switching node | Connects to inductor and Schottky catch diode anode; high dV/dt node requiring tight layout |
| VIN | Main power input | Accepts 8–50 V; requires local 22 µF/25 V ceramic + bulk electrolytic filtering |
Key Features
| Feature | Design Value |
|---|---|
| Integrated DMOS power switch | Eliminates external MOSFET and gate driver, reducing BOM count and layout complexity |
| Adjustable fixed off-time control | Enables stable operation across wide input/output ratios without loop compensation redesign |
| Cycle-skipping light-load mode | Maintains regulation down to microamp loads by skipping switching cycles, minimizing quiescent current |
| Internal 10 ms soft start | Prevents inrush-induced voltage droop on upstream supplies and avoids overstress on output capacitors |
| Thermal shutdown with hysteresis | 165°C trip with 15°C recovery margin prevents thermal oscillation during transient overloads |
Applications
| Printer Power Supplies | Consumer Equipment Power Supplies |
|---|---|
|
Use Scenario: Powering logic rails (3.3 V, 5 V) and motor drivers in inkjet/laser printers with 24–42 V DC bus. IC Role / Device Role / Timing Role: Primary step-down regulator converting high-voltage DC bus to stable low-voltage system rails. Use Value: Delivers 1.2 A at 3.3 V with >86% efficiency at full load, reducing heat sink requirements in compact printer enclosures. |
Use Scenario: Generating auxiliary 5 V/1.8 A rails in set-top boxes, DVD players, and audio amplifiers using 12 V wall adapters. IC Role / Device Role / Timing Role: High-efficiency buck converter replacing linear regulators to minimize thermal dissipation in sealed consumer enclosures. Use Value: Achieves 88% efficiency at 5 V/1.8 A, cutting standby power loss versus 7805-based solutions and meeting Energy Star requirements. |
| Industrial Control I/O Modules | Point-of-Sale Terminal Power |
|
Use Scenario: Providing isolated 12 V and 3.3 V rails from 24 V factory bus in programmable logic controller (PLC) I/O modules. IC Role / Device Role / Timing Role: Non-isolated primary regulator feeding downstream isolated DC/DC converters and microcontroller domains. Use Value: Withstands 50 V transients per IEC 61000-4-5, enabling direct connection to noisy 24 V industrial buses without additional TVS protection. |
Use Scenario: Converting 12 V adapter output to 3.3 V for ARM-based payment terminals operating in retail environments. IC Role / Device Role / Timing Role: Main system power regulator powering SoC, display, and secure element with tight voltage tolerance. Use Value: 1.200 V ±2% feedback reference ensures <±3% output regulation across line/load/temperature, meeting PCI PTS voltage stability requirements. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar high-voltage step-down regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| A4447 | Pin-compatible successor with enhanced efficiency (up to 92%), lower RDS(on) (300 mΩ), and extended temperature range (–40°C to 125°C). | Supports new designs requiring higher reliability and wider ambient operation; includes improved EMI performance. | Select A4447 for all new designs; migration path documented in Allegro transition notice dated June 2, 2015. |
| LM5164 | 3–65 V input, 1.5 A, adjustable frequency (100 kHz–2.2 MHz), no integrated boot diode - requires external bootstrap capacitor. | Better suited for space-constrained designs needing higher switching frequency and smaller magnetics. | Choose LM5164 when board area is limited and layout can accommodate external bootstrap components. |
Compared with A8499SLJTR-T, A4447 offers higher efficiency and broader temperature capability for new designs, while LM5164 provides frequency flexibility and higher input voltage margin but demands more external components and careful layout - both require schematic and layout revision.
Availability
A8499SLJTR-T is available at Aetrix Electronics and suitable for legacy printer power supplies, consumer equipment power supplies, and industrial control I/O modules requiring stable component supply for repair, replacement, or end-of-life inventory replenishment.
Supply support for A8499SLJTR-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 ICs, specializing in motion control, energy-efficient power conversion, and robust automotive-grade semiconductors.
The A8499 belongs to Allegro's high-voltage DC/DC regulator product line, engineered for cost-sensitive industrial and consumer applications requiring wide-input, adjustable-output buck conversion without external MOSFETs.
FAQ
Is A8499SLJTR-T still in production?
No, A8499SLJTR-T is a discontinued product. Allegro MicroSystems ceased production as of June 2, 2015. Samples are no longer available, and the device should not be purchased for new design applications. Aetrix Electronics maintains limited legacy stock for repair and replacement use only, with full traceability and documentation.
What is the correct pinout for A8499SLJTR-T?
The A8499SLJTR-T uses an 8-lead SOIC with exposed thermal pad (LJ package): Pin 1 = BOOT, Pin 2 = ENB, Pin 3 = TSET, Pin 4 = GND, Pin 5 = FB, Pin 6 = VBIAS, Pin 7 = LX, Pin 8 = VIN. The exposed pad is electrically connected to GND and must be soldered to the PCB thermal plane for proper thermal performance.
Can A8499SLJTR-T regulate 3.3 V output at 1.2 A?
Yes, A8499SLJTR-T is validated for 3.3 V/1.2 A operation using a 47 µH inductor, 100 µF/50 V output capacitor, and 17.8 kΩ/10.2 kΩ feedback divider. Efficiency exceeds 86% at full load, and thermal performance remains within spec with proper PCB thermal vias under 85°C ambient conditions.
What is the function of the TSET pin on A8499SLJTR-T?
The TSET pin on A8499SLJTR-T sets the fixed off-time via an external resistor to GND. For example, a 121 kΩ resistor yields ~15 µs off-time. This parameter directly affects minimum on-time compliance, switching frequency, and light-load behavior - undersized RTSET risks cycle skipping or instability at high VIN/VOUT ratios.
How does A8499SLJTR-T handle short-circuit conditions?
A8499SLJTR-T responds to short-circuit events by reducing the off-time multiplier based on FB voltage: if VFB falls below 0.5 V, off-time extends to 4× nominal to limit peak current to ~0.8 A. This protects the internal DMOS switch while maintaining control, unlike hard current-limit schemes that may cause thermal runaway.
A8499SLJTR-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):
- 1.2V
- Voltage - Output (Max):
- 24V
- Current - Output:
- -
- Frequency - Switching:
- -
- Synchronous Rectifier:
- No
- Operating Temperature:
- -20°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC-EP
A8499SLJTR-T FAQ
1.How can I place an order for A8499SLJTR-T through Aetrix?
Please submit a Request for Quotation (RFQ) for A8499SLJTR-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 A8499SLJTR-T reliable?
The price and inventory of A8499SLJTR-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A8499SLJTR-T is usually 5 days.
3.What payment methods are accepted for A8499SLJTR-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A8499SLJTR-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A8499SLJTR-T?
A8499SLJTR-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A8499SLJTR-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 A8499SLJTR-T?
For technical support, including A8499SLJTR-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A8499SLJTR-T requirements.
6.How does Aetrix verify that A8499SLJTR-T is sourced from the original manufacturer or authorized distributors?
All A8499SLJTR-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 A8499SLJTR-T meets industry standards.
7.What is the process for return or replacement of A8499SLJTR-T?
All A8499SLJTR-T units undergo pre-shipment inspection (PSI). If there is an issue with A8499SLJTR-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 A8499SLJTR-T part is unused and in its original packaging.
Return procedure for A8499SLJTR-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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