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Texas Instruments LM2585SX-12
- Part No.:
- LM2585SX-12
- Manufacturer:
- Texas Instruments
- Package:
- TO-263-6, D2PAK (5 Leads + Tab), TO-263BA
- Datasheet:
-
LM2585SX-12.pdf
- Description:
- IC REG BST FLYBACK 12V 3A TO263
- Quantity:
- Payment:
- Shipping:
Inventory:4,817
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Product details
Overview
LM2585SX-12 from Texas Instruments (formerly National Semiconductor) is a monolithic 3A flyback/boost regulator IC with fixed 12V output, 100 kHz fixed-frequency oscillator, NPN internal switch rated for 65V standoff and 3.0A current, and ±4% system output voltage tolerance over line and load. It operates from 4V to 40V input and is used in isolated DC-DC power supplies for industrial control and telecom interface modules.
For engineers reviewing the LM2585SX-12 datasheet, LM2585SX-12 pinout, LM2585SX-12 application, or LM2585SX-12 equivalent, key selection criteria include its TO-263-5 package thermal performance (θJA = 26°C/W with 7.4× copper), 12V fixed-output architecture, flyback topology support, and absence of external feedback resistor network.
Technical Context
The LM2585SX-12 implements current-mode control with cycle-by-cycle current limiting, internal soft-start (11 μA soft-start current), and undervoltage lockout (3.30V threshold). Its error amplifier features 70 V/V voltage gain and 0.328 mmho transconductance at 25°C, with reference voltage of 12.0V (±0.48V min/max) measured at the feedback pin under specified conditions.
It integrates a 100 kHz oscillator (±15 kHz variation over temperature), supports duty cycles up to 98%, and delivers 93% efficiency at 10V input and 0.6A load in boost configuration. The NPN switch exhibits 0.45V saturation voltage at 3.0A and sustains 65V in off-state.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | Fixed 12.0V ±4% over full line/load/temperature range - eliminates need for external feedback resistors. |
| Input Voltage Range | 4V to 40V - supports wide-range industrial and automotive battery inputs without pre-regulation. |
| Switch Current Limit | 3.0A typical - sets maximum peak inductor current in flyback/boost topologies. |
| Oscillator Frequency | 100 kHz ±15 kHz - enables use of compact magnetics while balancing EMI and efficiency. |
| Thermal Resistance θJA | 26°C/W with 7.4× package-area copper - enables high-power operation without external heatsink in PCB-integrated thermal design. |
| Efficiency | 93% at VIN = 10V, IOUT = 0.6A - reflects optimized switching loss and conduction loss in 12V boost configuration. |
| Reference Voltage | 12.0V (min 11.52V / max 12.48V) - defines regulated output accuracy and stability across operating conditions. |
Pinout & Package
LM2585SX-12 is housed in a 5-lead TO-263 (S) surface-mount package (NSC TS5B), with exposed metal tab thermally and electrically connected to Pin 2 (Ground). The package supports high-current routing and low thermal resistance when soldered to ≥1.0064 in² of 1 oz. copper.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - Input | Power input supply connection | Accepts 4–40V DC; requires ≥100 μF bulk + 0.1 μF ceramic bypass capacitance near pin. |
| 2 - Ground | Circuit common reference and thermal path | Internally tied to exposed tab; must be soldered to large copper pour for thermal management. |
| 3 - Feedback | Output voltage sensing node | Internally connected to 12V reference; no external resistor divider required for fixed-output operation. |
| 4 - Switch | Collector of internal NPN power transistor | Drives primary winding of flyback transformer or boost inductor; withstands 65V off-state. |
| 5 - Compensation | Error amplifier output for loop stabilization | Connect RC network (e.g., 2kΩ + 0.47 μF) to set pole-zero for stable flyback/boost control loop. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 3A/65V NPN switch | Eliminates external transistor and drive circuitry; reduces BOM count and layout complexity in flyback designs. |
| Current-mode control | Provides inherent line and load transient immunity, simplifies loop compensation, and enables reliable cycle-by-cycle current limiting. |
| Internal soft-start | 11 μA soft-start current limits inrush into input capacitors and prevents output overshoot during power-up. |
| Undervoltage lockout (UVLO) | 3.30V turn-on threshold prevents erratic operation during brownout or cold-start conditions. |
| Fixed 12V output configuration | Removes feedback resistor selection errors and drift; guarantees output accuracy without calibration. |
Applications
| Industrial Isolated Power Supply | Telecom Interface Module |
|---|---|
|
Use Scenario: Generating isolated 12V rail from 24V DC bus in programmable logic controller (PLC) backplane. IC Role / Device Role / Timing Role: Flyback controller regulating isolated secondary output using Schott transformer T6 with 1.2:1 turns ratio. Use Value: Delivers 0.6A at 12V with 93% efficiency and survives short-circuit via frequency foldback to 25 kHz. |
Use Scenario: Providing 12V bias for RS-485 transceivers and optocouplers in fieldbus gateway. IC Role / Device Role / Timing Role: Boost regulator stepping 5V USB-derived input to stable 12V output with minimal external components. Use Value: Achieves ±4% regulation across −40°C to +125°C junction temperature without trimming or feedback adjustment. |
| Automotive Body Control Unit | Test Equipment Auxiliary Supply |
|
Use Scenario: Deriving 12V from vehicle battery (9–16V) for microcontroller peripherals in door module. IC Role / Device Role / Timing Role: Flyback regulator with Renco RL-5533 transformer, leveraging internal UVLO to prevent startup below 3.3V. Use Value: Maintains regulation during cold-crank (4V input) and load dump (40V input) per ISO 7637-2 requirements. |
Use Scenario: On-board 12V supply for analog front-end circuitry in portable DMM or signal generator. IC Role / Device Role / Timing Role: Step-up regulator converting 3.3V/5V system rail to 12V for op-amp biasing and DAC reference. Use Value: Enables compact, low-noise 12V source with only inductor, diode, and two capacitors-no external feedback network. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar flyback/boost regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LM2585T-12 | Same die, but in through-hole TO-220-5 (T05D) package with θJA = 45°C/W (no heatsink) vs. 26°C/W for LM2585SX-12 on large copper. | Requires PCB mounting with vertical leads and socket or soldered leads; less suitable for high-density SMT layouts. | Select LM2585T-12 only when manual assembly, prototyping, or legacy through-hole compatibility is required. |
| LM2577-12 | Different architecture: 3A step-up-only regulator with 52 kHz oscillator, no flyback capability, and adjustable soft-start via external capacitor. | Lacks transformer-driven isolation; limited to non-isolated boost applications where ground-referenced 12V is acceptable. | Choose LM2577-12 only for cost-sensitive, non-isolated boost designs where 52 kHz EMI profile is preferred and isolation is unnecessary. |
Compared with LM2585T-12 and LM2577-12, the LM2585SX-12 offers superior thermal performance in SMT production, native flyback topology support, and fixed-output simplicity-making it optimal for volume-manufactured isolated 12V supplies.
Availability
LM2585SX-12 is available at Aetrix Electronics and suitable for industrial control systems, telecom interface modules, and automotive body electronics requiring stable component supply with long-term lifecycle assurance.
Supply support for LM2585SX-12 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
Texas Instruments acquired National Semiconductor in 2011 and maintains full technical and manufacturing continuity for the SIMPLE SWITCHER® product line.
The LM2585SX-12 belongs to the SIMPLE SWITCHER® family of integrated switching regulators, designed specifically for cost-effective, low-component-count flyback and boost power conversion in industrial and embedded applications.
FAQ
What topology does the LM2585SX-12 support?
The LM2585SX-12 supports flyback, boost (step-up), and forward converter topologies. Its internal 3A/65V NPN switch, current-mode control, and 100 kHz oscillator make it especially suited for isolated flyback designs using standard transformers like Renco RL-5533 or Coilcraft Q4339-B. It does not support buck (step-down) operation.
Does the LM2585SX-12 require external feedback resistors?
No. The LM2585SX-12 is a fixed-output variant with internal 12V reference connected directly to the Feedback pin (Pin 3), eliminating the need for external resistor dividers. This ensures ±4% output accuracy without calibration or component tolerance drift affecting regulation.
What is the maximum continuous output current for LM2585SX-12 in flyback mode?
In flyback configuration with appropriate transformer selection (e.g., Renco RL-5533), the LM2585SX-12 delivers up to 0.6A continuously at 12V output while maintaining regulation and thermal safety. Output current is internally limited in flyback mode, unlike boost mode where external current limiting is required.
How does the LM2585SX-12 handle short-circuit conditions?
In flyback mode, the LM2585SX-12 responds to output short-circuit by reducing switching frequency from 100 kHz to 25 kHz (short-circuit frequency), extending off-time to fully discharge transformer energy and enabling zero-current turn-on. This protects the internal NPN switch without requiring external circuitry.
What thermal considerations apply to the LM2585SX-12 in TO-263 package?
The LM2585SX-12 achieves θJA = 26°C/W when mounted on 1.0064 in² of 1 oz. copper - critical for sustaining 3A switch current at elevated ambient temperatures. The exposed tab (Pin 2) must be soldered to this copper area; insufficient copper or poor solder joint increases junction temperature and risks thermal shutdown.
LM2585SX-12 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- SIMPLE SWITCHER®
- Package/Case:
- TO-263-6, D2PAK (5 Leads + Tab), TO-263BA
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Function:
- Step-Up, Step-Up/Step-Down
- Output Configuration:
- Positive
- Topology:
- Boost, Flyback, Forward Converter
- Output Type:
- Fixed
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 4V
- Voltage - Input (Max):
- 40V
- Voltage - Output (Min/Fixed):
- 12V
- Voltage - Output (Max):
- -
- Current - Output:
- 3A (Switch)
- Frequency - Switching:
- 100kHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- TO-263 (DDPAK-5)
LM2585SX-12 FAQ
1.How can I place an order for LM2585SX-12 through Aetrix?
Please submit a Request for Quotation (RFQ) for LM2585SX-12 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 LM2585SX-12 reliable?
The price and inventory of LM2585SX-12 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM2585SX-12 is usually 5 days.
3.What payment methods are accepted for LM2585SX-12?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM2585SX-12 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM2585SX-12?
LM2585SX-12 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM2585SX-12 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 LM2585SX-12?
For technical support, including LM2585SX-12 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM2585SX-12 requirements.
6.How does Aetrix verify that LM2585SX-12 is sourced from the original manufacturer or authorized distributors?
All LM2585SX-12 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 LM2585SX-12 meets industry standards.
7.What is the process for return or replacement of LM2585SX-12?
All LM2585SX-12 units undergo pre-shipment inspection (PSI). If there is an issue with LM2585SX-12, 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 LM2585SX-12 part is unused and in its original packaging.
Return procedure for LM2585SX-12:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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