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Texas Instruments LM2585S-12
- Part No.:
- LM2585S-12
- Manufacturer:
- Texas Instruments
- Package:
- TO-263-6, D2PAK (5 Leads + Tab), TO-263BA
- Datasheet:
-
LM2585S-12.pdf
- Description:
- IC REG BST FLYBACK 12V 3A TO263
- Quantity:
- Payment:
- Shipping:
Inventory:1,064
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Product details
Overview
LM2585S-12 from Texas Instruments (formerly National Semiconductor) is a monolithic 3A flyback/boost regulator IC with fixed 12V output, integrated 65V NPN power switch, 100 kHz fixed-frequency oscillator, and current-mode control architecture. It delivers ±4% output voltage tolerance over line and load, supports 4V–40V input, and is used in isolated DC-DC converters for industrial power supplies and telecom interface modules.
For engineers reviewing the LM2585S-12 datasheet, LM2585S-12 pinout, LM2585S-12 application, or LM2585S-12 equivalent, this page provides verified technical context, package-specific thermal data, confirmed pin functions, real-world flyback/boost implementation constraints, and validated alternative parts for 12V switching regulator designs.
Technical Context
The LM2585S-12 implements current-mode PWM control with cycle-by-cycle current limiting, internal soft-start (11 μA compensation pin current), and undervoltage lockout (3.3 V threshold). Its error amplifier features 70 V/V open-loop gain and 0.328 mmho transconductance at 25°C, referenced to a 12.0 V internal feedback node.
It operates exclusively in flyback or boost topologies - not buck - and requires external magnetics: 15 μH inductor for boost (Figure 3), or transformer T7 (1:1.2 turns ratio) for flyback. Output regulation relies on direct sensing of the 12V output via internal resistor divider; no external feedback resistors are needed.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | Fixed 12.0 V ±4% over 4V–10V input and 0.2A–0.8A load - guarantees stable rail for downstream logic or analog circuitry without trimming. |
| Input Voltage Range | 4V to 40V - supports wide-input industrial rails including 5V, 12V, 24V, and 36V bus systems. |
| Switch Current Limit | 3.0 A peak - sets maximum energy transfer per cycle; output current must be externally limited to 3A in boost mode. |
| Oscillator Frequency | 100 kHz (±15%) - enables use of compact, low-cost magnetics while maintaining EMI below 150 kHz fundamental. |
| Thermal Resistance (θJA) | 26°C/W (TO-263, 7.4× copper area) - defines minimum PCB copper area required for 125°C max junction temperature at full load. |
| Efficiency | 93% at VIN = 10V, IOUT = 0.6A - measured in flyback configuration (Figure 3); drops significantly under light load or high VIN. |
| Reference Voltage | 12.0 V at feedback pin - internally trimmed; ΔVREF ≤ 7.8 mV over 4V–40V input - ensures tight output setpoint stability. |
Pinout & Package
LM2585S-12 uses the 5-lead TO-263 (S) package (NSC TS5B), surface-mount, with exposed thermal pad soldered to PCB copper for heat dissipation. Pin 3 (GND) and Pin 5 (VIN) connect to internal ground and input supply planes; Pin 4 (SW) carries high dv/dt switching node.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| Pin 1 (COMP) | Error amplifier output | Provides transconductance-controlled signal (0.25–2.8 V swing) to modulate duty cycle; requires RC network for loop stability. |
| Pin 2 (FB) | Feedback input | Internally connected to 12V divider; unused in fixed-output version - must be left unconnected or tied to GND per datasheet. |
| Pin 3 (GND) | Power and signal ground | Common return for internal circuits, switch emitter, and external components; must be low-impedance connection to thermal pad. |
| Pin 4 (SW) | Switch collector | Drives primary winding of flyback transformer or boost inductor; sees up to 65V reverse bias and high-frequency ringing - requires snubber. |
| Pin 5 (VIN) | Input supply | Accepts 4–40V DC; powers internal bias circuits and switch base drive; requires ≥100 μF bulk + 0.1 μF ceramic bypass near pin. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 3A/65V NPN switch | Eliminates external transistor and base drive circuitry; reduces BOM count and layout complexity in flyback/boost designs. |
| Current-mode control | Enables inherent line/load transient rejection and simplifies loop compensation - no external slope compensation needed. |
| Internal soft-start | 11 μA COMP pin current limits inrush during startup, preventing input rail sag and output overshoot in multi-rail systems. |
| Thermal shutdown & UVLO | Protects against sustained overload (TJ > 150°C) and brownout (VIN < 3.05V); device resumes operation after fault clearance. |
| Fixed 12V output topology | Removes need for external feedback resistors - improves accuracy, reduces drift, and avoids layout sensitivity in high-noise environments. |
Applications
| Industrial Flyback Power Supply | Telecom Interface Boost Converter |
|---|---|
|
Use Scenario: Isolated 12V/0.8A output powering RS-485 transceivers and microcontroller peripherals from 24V DC bus. IC Role / Device Role / Timing Role: Primary-side controller implementing flyback topology with T7 transformer (1:1.2), regulating output via primary-side sensing. Use Value: Achieves ±4% output tolerance without optocoupler or secondary-side feedback - reduces component count and improves reliability. |
Use Scenario: Non-isolated +12V rail generation from +5V USB-C PD source for analog front-end circuitry in field instruments. IC Role / Device Role / Timing Role: Boost regulator using 15 μH inductor and 1N5820 Schottky diode; 100 kHz switching minimizes EMI in mixed-signal PCBs. Use Value: Delivers 93% efficiency at 0.6A load - extends battery life and reduces thermal stress compared to linear regulators. |
| Automotive Body Control Module | Medical Sensor Bias Supply |
|
Use Scenario: 12V auxiliary rail derived from 12V vehicle battery (4V–16V cold-crank range) for CAN transceiver and LED drivers. IC Role / Device Role / Timing Role: Flyback regulator with Renco RL-5751 transformer; UVLO prevents startup below 3.3V - critical for cold-crank immunity. Use Value: Withstands 40V load-dump transients on VIN pin - eliminates need for external TVS when used with proper input filtering. |
Use Scenario: Low-noise 12V bias for precision op-amps and ADC reference buffers in portable ultrasound sensors. IC Role / Device Role / Timing Role: Boost converter with ceramic output capacitor and RC input filter (Figure 40); soft-start prevents sensor reset during power-up. Use Value: Output ripple <50 mVpp (Figure 6) meets medical-grade analog supply requirements without additional LDO post-regulation. |
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, 5-lead TO-220 (T05D) package; θJA = 45°C/W (4 in² copper) vs. 26°C/W for S-package - requires larger heatsink area. | Through-hole mounting; better suited for prototyping or low-volume manual assembly; less suitable for high-density automated PCBs. | Select LM2585T-12 only if TO-220 mechanical fit or thermal test conditions match legacy designs - not drop-in compatible with TO-263 footprint. |
| LM2577S-12 | Different architecture: 3A step-up-only (no flyback support); 50 kHz switching; lower quiescent current (11 mA vs. 15.5 mA); no internal soft-start. | Limited to non-isolated boost; cannot replace LM2585S-12 in flyback or multiple-output transformer-based designs. | Choose LM2577S-12 only for cost-sensitive, low-EMI boost applications where isolation and transformer flexibility are unnecessary. |
Compared with LM2585T-12 and LM2577S-12, the LM2585S-12 uniquely combines surface-mount TO-263 packaging, flyback capability, and fixed 12V output - enabling compact, isolated power designs with minimal external components and guaranteed ±4% regulation.
Availability
LM2585S-12 is available at Aetrix Electronics and suitable for industrial power supplies, telecom interface modules, and automotive body control units requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LM2585S-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 product support, datasheet archives, and application engineering resources for the SIMPLE SWITCHER® portfolio.
The LM2585S-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, telecom, and automotive applications.
FAQ
What is the maximum input voltage rating for the LM2585S-12?
The absolute maximum input voltage for the LM2585S-12 is 45V, but the recommended operating range is 4V to 40V. Exceeding 40V risks violating the 65V switch voltage limit under flyback off-state conditions - especially with transformer leakage - and may trigger thermal shutdown or permanent damage. Always verify VSW(OFF) = VIN(Max) + (VOUT + VF)/N remains ≤65V in your design.
Can the LM2585S-12 be used in buck (step-down) topology?
No, the LM2585S-12 cannot be used in buck topology. Its internal NPN switch and control architecture are optimized for flyback and boost configurations only. The datasheet explicitly states it is "designed for flyback, step-up (boost), and forward converter applications" - buck operation is unsupported and will result in failure due to incorrect switch placement and lack of synchronous rectification capability.
What is the purpose of the COMP pin on the LM2585S-12?
The COMP pin on the LM2585S-12 is the error amplifier output, providing a transconductance-controlled voltage (0.25–2.8 V) that directly modulates the PWM comparator threshold. It must be connected to an external RC compensation network (e.g., 2 kΩ + 0.47 μF per Figure 3) to stabilize the control loop - omitting this network causes oscillation and output instability.
Does the LM2585S-12 require external feedback resistors?
No, the LM2585S-12 does not require external feedback resistors. As a fixed-output variant, its 12V regulation is implemented with an internal resistor divider connected to the FB pin. The FB pin must remain unconnected or tied to GND per datasheet guidance - adding external resistors will disrupt regulation and cause overvoltage or instability.
How does short-circuit protection work in flyback mode for the LM2585S-12?
In flyback mode, the LM2585S-12 responds to main-output short circuits by reducing switching frequency from 100 kHz to 25 kHz (per Figure 39), extending off-time to fully discharge transformer energy before next cycle. This allows zero-current turn-on and engages internal current limiting to protect the 3A NPN switch - unlike boost mode, where external current limiting is mandatory.
LM2585S-12 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- SIMPLE SWITCHER®
- Package/Case:
- TO-263-6, D2PAK (5 Leads + Tab), TO-263BA
- Packaging:
- Tube
- 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)
LM2585S-12 FAQ
1.How can I place an order for LM2585S-12 through Aetrix?
Please submit a Request for Quotation (RFQ) for LM2585S-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 LM2585S-12 reliable?
The price and inventory of LM2585S-12 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM2585S-12 is usually 5 days.
3.What payment methods are accepted for LM2585S-12?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM2585S-12 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM2585S-12?
LM2585S-12 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM2585S-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 LM2585S-12?
For technical support, including LM2585S-12 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM2585S-12 requirements.
6.How does Aetrix verify that LM2585S-12 is sourced from the original manufacturer or authorized distributors?
All LM2585S-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 LM2585S-12 meets industry standards.
7.What is the process for return or replacement of LM2585S-12?
All LM2585S-12 units undergo pre-shipment inspection (PSI). If there is an issue with LM2585S-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 LM2585S-12 part is unused and in its original packaging.
Return procedure for LM2585S-12:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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