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Allegro MicroSystems A8499SLJ-T
- Part No.:
- A8499SLJ-T
- Manufacturer:
- Allegro MicroSystems
- Package:
- 8-SOIC (0.154", 3.90mm Width) Exposed Pad
- Datasheet:
-
A8499SLJ-T.pdf
- Description:
- IC REG BUCK ADJ 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,395
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Product details
Overview
A8499SLJ-T from Allegro MicroSystems is a high-voltage step-down DC/DC regulator IC featuring 8–50 V input range, adjustable 1.2–24 V output, and integrated 700 mΩ DMOS switch. It delivers up to 1.2 A at 3.3 V in a thermally enhanced 8-lead SOIC-LJ package, designed for printer and consumer equipment power supplies.
For engineers reviewing the A8499SLJ-T datasheet, A8499SLJ-T pinout, A8499SLJ-T application, or A8499SLJ-T equivalent, key selection criteria include fixed off-time current-mode control, thermal shutdown at 165°C, soft-start timing (10 ms nominal), feedback reference voltage (1.200 V ±2%), and discontinuation status requiring legacy design support planning.
Technical Context
The A8499SLJ-T implements fixed off-time, current-mode control with external TSET resistor programming (e.g., 121 kΩ sets ~180 µs off-time). It operates in continuous or discontinuous conduction mode and includes internal blanking (200 ns) to suppress diode reverse-recovery transients.
Regulation relies on a precision 1.200 V ±2% internal reference and feedback bias current (±100 nA). Protection features include undervoltage lockout (6.9–7.1 V), cycle-skipping light-load mode, and short-circuit response with FB-voltage-dependent off-time extension (e.g., 4×tOFF if VFB < 0.5 V).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 8–50 V - supports wide-range industrial and automotive inputs without pre-regulation |
| Output Voltage Range | 1.2–24 V - set via external R1/R2 divider using 1.200 V ±2% internal reference |
| Max Output Current | 1.2 A - limited by 2.2 A minimum current limit and thermal resistance (RθJA = 35°C/W) |
| Switch RDS(on) | 700–800 mΩ @ 25°C - determines conduction loss and thermal rise at full load |
| Feedback Reference | 1.200 V ±2% - enables ±3% output regulation over 0–2 A load and temperature |
| Soft Start Time | 5–15 ms - controls inrush current during startup to limit input supply stress |
| Thermal Shutdown | 165°C - protects against sustained overload; 15°C hysteresis ensures stable recovery |
Pinout & Package
Package: 8-lead SOIC with exposed thermal pad (suffix LJ); 4-layer PCB layout recommended with thermal vias under pad for RθJA = 35°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| BOOT | Gate drive boost node | Supplies charge to high-side MOSFET gate; requires 0.01 µF ceramic capacitor to LX |
| ENB | Enable logic input | Pulled low to enable; open-circuit disables output and decays to 0 V |
| TSET | Fixed off-time programming | Resistor to GND sets tOFF (e.g., 121 kΩ → ~180 µs); critical for min-on-time compliance |
| GND | Power and signal ground | Common return for bias, feedback, and thermal pad; must be low-impedance |
| FB | Feedback input | Monitors output via resistor divider; triggers 0.8 A short-circuit limit if <0.5 V |
| VBIAS | Bias supply input | Connected to VOUT when target is 3.3–5 V 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 supply input | Accepts 8–50 V; includes 6.9–7.1 V UVLO with 0.7–1.1 V hysteresis |
Key Features
| Feature | Design Value |
|---|---|
| Integrated DMOS switch | 700 mΩ RDS(on) eliminates external FET and reduces BOM count in compact designs |
| Adjustable fixed off-time | Programmable via single RTSET resistor - enables precise frequency and stability tuning across input/output ratios |
| Current-mode control | Inherent cycle-by-cycle current limiting and fast transient response without external compensation |
| Light-load cycle skipping | Maintains regulation down to zero load without external bias supply or burst-mode noise |
| VBIAS optimization | Auto-switches bias source between VOUT (3.3–5 V outputs) and VIN - improves full-load efficiency by ~5% |
Applications
| Printer Power Supplies | Consumer Equipment Power Supplies |
|---|---|
Use Scenario: Provides 3.3 V/1.2 A rail for logic and interface circuitry in inkjet/laser printers with 42 V input bus. IC Role / Device Role / Timing Role: Primary non-isolated buck regulator converting high-voltage printer supply to low-voltage logic domain. Use Value: Eliminates need for external high-voltage FET and simplifies EMI filtering with fixed off-time architecture. | Use Scenario: Generates 5 V/1.8 A for set-top box mainboard from 12 V adapter input. IC Role / Device Role / Timing Role: Adjustable-output step-down controller managing dynamic load steps during video decoding bursts. Use Value: Cycle-skipping mode maintains <±3% regulation at microamp loads, extending standby battery life. |
| Industrial Control Power | Automotive Aftermarket Accessories |
Use Scenario: Delivers 12 V/1.0 A to PLC I/O modules from 24–48 V field bus. IC Role / Device Role / Timing Role: High-input-voltage regulator with UVLO hysteresis preventing brownout oscillation in noisy factory environments. Use Value: 165°C thermal shutdown and 35°C/W thermal resistance enable reliable operation in enclosed enclosures. | Use Scenario: Powers 3.3 V MCU and sensors in vehicle dashcam from 12–16 V battery with load dump immunity. IC Role / Device Role / Timing Role: Input-stage buck converter handling cold-crank (6.9 V UVLO) and load-dump (50 V abs max) conditions. Use Value: Integrated 50 V absolute max rating and 700 mΩ switch reduce external TVS and FET count. |
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 | Successor device with improved efficiency (up to 92%), lower RDS(on) (350 mΩ), and extended 55 V abs max rating | Designed for new designs; supports higher output currents and tighter thermal constraints | Select A4447 for new projects requiring longer product lifecycle and higher performance |
| A8499 | Same die and functionality; A8499SLJ-T is the tape-and-reel variant of A8499 in LJ package | No functional difference - identical electrical specs, pinout, and thermal behavior | A8499SLJ-T is the production-orderable version; A8499 refers to base part number in documentation |
Compared with A4447 and A8499, the A8499SLJ-T offers identical performance and pin compatibility but is discontinued - A4447 provides forward-compatible replacement with higher efficiency and voltage margin, while A8499 is a documentation alias rather than a distinct alternative.
Availability
A84499SLJ-T is available at Aetrix Electronics and suitable for printer power supplies, consumer equipment power supplies, and industrial control power requiring stable component supply despite end-of-life status.
Supply support for A8499SLJ-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 Hall-effect sensors, motor drivers, and power ICs, founded in 1989 and headquartered in Manchester, NH.
The A8499SLJ-T belongs to Allegro's high-voltage DC/DC regulator product line, engineered for robust operation in 8–50 V input systems where reliability under thermal and voltage stress is critical.
FAQ
Is the A8499SLJ-T still in production?
No, the A8499SLJ-T is a discontinued product. Allegro MicroSystems ceased production as of June 2, 2015. It is not recommended for new designs, and samples are no longer available. Aetrix Electronics supports legacy procurement with verified stock and traceable sourcing for ongoing maintenance and repair programs involving the A8499SLJ-T.
What is the correct pinout for the A8499SLJ-T?
Pin 1 is BOOT, Pin 2 is ENB, Pin 3 is TSET, Pin 4 is GND, Pin 5 is FB, Pin 6 is VBIAS, Pin 7 is LX, and Pin 8 is VIN. The exposed thermal pad is electrically connected to GND and must be soldered to a thermal plane. This pinout matches the SOIC-LJ package drawing in the A8499 datasheet Rev. 6 and is confirmed for the A8499SLJ-T variant.
Can the A8499SLJ-T regulate output voltage below 3.3 V?
Yes, the A8499SLJ-T supports output voltages from 1.2 V to 24 V via external resistor divider on the FB pin. However, VBIAS must be supplied externally or from VIN (not VOUT) when VOUT is below 3.3 V, as internal bias switching only activates for 3.3–5 V targets. This reduces efficiency but maintains full functionality down to 1.2 V.
What is the maximum switching frequency of the A8499SLJ-T?
The A8499SLJ-T does not have a fixed switching frequency - it uses fixed off-time control, so fSW varies with input/output voltage and load. For example, at VIN = 42 V, VOUT = 3.3 V, and IOUT = 1.2 A, typical fSW is ~120 kHz. Frequency increases with higher VIN/VOUT ratios and decreases under light load due to cycle skipping.
Does the A8499SLJ-T require an external Schottky diode?
Yes, the A8499SLJ-T requires an external Schottky catch diode (e.g., B340) connected between LX and VOUT. The IC integrates only the high-side DMOS switch; the diode provides the return path during switch-off. Diode selection must account for 1.2× maximum load current and voltage rating exceeding VIN(max) - critical for reliability in 42 V applications.
A8499SLJ-T Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Allegro MicroSystems
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width) Exposed Pad
- Packaging:
- Tube
- 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
A8499SLJ-T FAQ
1.How can I place an order for A8499SLJ-T through Aetrix?
Please submit a Request for Quotation (RFQ) for A8499SLJ-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 A8499SLJ-T reliable?
The price and inventory of A8499SLJ-T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for A8499SLJ-T is usually 5 days.
3.What payment methods are accepted for A8499SLJ-T?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for A8499SLJ-T transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for A8499SLJ-T?
A8499SLJ-T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your A8499SLJ-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 A8499SLJ-T?
For technical support, including A8499SLJ-T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your A8499SLJ-T requirements.
6.How does Aetrix verify that A8499SLJ-T is sourced from the original manufacturer or authorized distributors?
All A8499SLJ-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 A8499SLJ-T meets industry standards.
7.What is the process for return or replacement of A8499SLJ-T?
All A8499SLJ-T units undergo pre-shipment inspection (PSI). If there is an issue with A8499SLJ-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 A8499SLJ-T part is unused and in its original packaging.
Return procedure for A8499SLJ-T:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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