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Texas Instruments LM2585SX-ADJ
- Part No.:
- LM2585SX-ADJ
- Manufacturer:
- Texas Instruments
- Package:
- TO-263-6, D2PAK (5 Leads + Tab), TO-263BA
- Datasheet:
-
LM2585SX-ADJ.pdf
- Description:
- IC REG BST FLYBACK ADJ 3A TO263
- Quantity:
- Payment:
- Shipping:
Inventory:1,422
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Product details
Overview
LM2585SX-ADJ from Texas Instruments (formerly National Semiconductor) is a monolithic 3A flyback/boost regulator IC with adjustable output voltage, 100 kHz fixed-frequency current-mode control, 4V–40V input range, and integrated 3.0A/65V NPN switch. It delivers ±4% system output voltage tolerance over line and load, supports soft-start, thermal shutdown, and undervoltage lockout - used in isolated DC-DC converters for industrial power supplies and telecom interfaces.
For engineers reviewing the LM2585SX-ADJ datasheet, LM2585SX-ADJ pinout, LM2585SX-ADJ application, or LM2585SX-ADJ equivalent, this page provides verified technical context, validated pin functions, confirmed design parameters including VREF = 1.230 V, ISWITCH = 3.0 A, fSW = 100 kHz, θJA = 35°C/W (TO-263), and real-world application constraints for flyback and boost topologies.
Technical Context
The LM2585SX-ADJ implements current-mode control with cycle-by-cycle peak current limiting and a 100 kHz internal oscillator, enabling stable regulation under wide input (4–40 V) and load transients. Its error amplifier features 670 V/V gain and 3.2 mmho transconductance, referenced to a precision 1.230 V internal bandgap.
It operates in flyback, boost, or forward converter topologies using external magnetics and diodes. The NPN power switch sustains up to 65 V with 0.45 V saturation voltage at 3.0 A, protected by thermal shutdown, UVLO (3.30 V threshold), and internal current limit (4.0 A typical).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | Adjustable via external resistor divider; set by VOUT = 1.230 V × (1 + R1/R2) |
| Input Voltage Range | 4 V to 40 V - supports wide-input industrial and automotive battery-fed systems |
| Switch Current Limit | 3.0 A typical - defines maximum peak inductor current in boost; internally limited in flyback |
| Switching Frequency | 100 kHz ±15% - enables use of compact magnetics and predictable EMI filtering |
| Reference Voltage | 1.230 V ±2.2 mV - high-accuracy feedback reference enabling tight output regulation |
| Thermal Resistance | θJA = 35°C/W (TO-263 on 7.4× package copper) - enables 3A operation without external heatsink at ≤60°C ambient |
| Soft-Start Current | 11.0 μA typical - controls ramp rate of output voltage during startup to limit inrush |
Pinout & Package
LM2585SX-ADJ is housed in a 5-lead TO-263 (S) surface-mount package (NSC TS5B), with exposed thermal pad for enhanced heat dissipation. Mounting requires soldering the tab to ≥1.0064 in² of 1 oz. copper for rated 35°C/W θJA.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - Input (VIN) | Power input supply connection | Accepts 4–40 V DC; bypassed externally with 100 μF + 0.1 μF capacitors |
| 2 - Ground (GND) | Circuit common reference | Return path for internal circuits and external feedback network; must be low-impedance |
| 3 - Feedback (FB) | Output voltage sensing node | Compares divided output against 1.230 V reference; sets regulation point |
| 4 - Switch (SW) | Collector of internal NPN transistor | Drives external transformer primary or boost inductor; switches at 100 kHz |
| 5 - Compensation (COMP) | Error amplifier output | Provides loop compensation node; connects RC network for stability |
Key Features
| Feature | Design Value |
|---|---|
| Current-mode control | Enables fast transient response and inherent cycle-by-cycle current limiting without slope compensation |
| Integrated 3.0A/65V NPN switch | Eliminates need for external high-voltage switching transistor in flyback/boost designs |
| Internal soft-start | Reduces input inrush current and prevents output overshoot during power-up |
| Undervoltage lockout (UVLO) | Disables operation below 3.30 V to prevent erratic startup and ensure stable biasing |
| Thermal shutdown protection | Shuts down at 150°C junction temperature and auto-restarts after cooldown |
Applications
| Flyback Regulator | Boost Regulator |
|---|---|
Use Scenario: Isolated 12 V output from 8–16 V automotive battery rail with multiple secondary windings for auxiliary rails. IC Role / Device Role / Timing Role: Primary-side controller regulating main output via optocoupler feedback; 100 kHz switching defines transformer size and EMI profile. Use Value: Enables single-chip isolation with ±4% output tolerance across temperature and load, eliminating need for post-regulation LDOs. |
Use Scenario: Generating 24 V from a 12 V supply in industrial PLC I/O modules requiring >1 A output current. IC Role / Device Role / Timing Role: Boost controller driving external inductor and Schottky diode; fixed 100 kHz frequency simplifies filter design. Use Value: Delivers regulated 24 V at up to 1.2 A with no external MOSFET or gate driver, reducing BOM count and layout complexity. |
| Dual-Output Flyback | Telecom Interface Power |
Use Scenario: Providing +12 V/0.6 A and −12 V/0.25 A from a 4–6 V input in analog signal conditioning circuitry. IC Role / Device Role / Timing Role: Primary-side controller managing cross-regulation between outputs using standard T6 transformer (1.2:1.2 turns ratio). Use Value: Achieves dual-rail isolation with <100 mV load regulation per rail, avoiding separate regulators and minimizing transformer count. |
Use Scenario: Generating isolated ±12 V bias for RS-485 transceivers and op-amps in noisy factory-floor communication nodes. IC Role / Device Role / Timing Role: Flyback controller operating at 100 kHz to meet CISPR-22 Class B conducted EMI limits; uses Schottky clamp to suppress switch-node ringing. Use Value: Provides noise-immune, isolated bias with built-in UVLO and thermal protection - critical for unattended remote equipment reliability. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar flyback/boost regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LM2587SX-ADJ | Higher 5A switch rating, same 100 kHz frequency and adjustable output; requires larger inductor and heatsinking | Better suited for >2.5A continuous output; not drop-in due to different thermal pad layout and higher ISW | Select when output current exceeds 2.5A or input voltage exceeds 40V (LM2587 supports 65V VIN) |
| UCC38C43D | Current-mode PWM controller only - no integrated switch; requires external NPN/MOSFET and gate drive | Offers greater flexibility in switch selection and higher efficiency at light loads; lacks integrated UVLO and soft-start | Choose when designing custom high-efficiency or high-reliability flyback with discrete switch optimization |
Compared with LM2585SX-ADJ, LM2587SX-ADJ supports higher output current but increases board area and thermal management complexity, while UCC38C43D offers design flexibility at the cost of added external components and reduced integration.
Availability
LM2585SX-ADJ is available at Aetrix Electronics and suitable for industrial power supplies, telecom interface modules, and embedded DC-DC converters requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for LM2585SX-ADJ 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 LM2585 series was designed specifically for cost-sensitive, medium-power isolated and non-isolated DC-DC conversion in industrial, telecom, and automotive subsystems - emphasizing minimal external parts and robust protection.
FAQ
What is the function of the COMP pin on the LM2585SX-ADJ?
The COMP pin on the LM2585SX-ADJ is the output of the internal error amplifier and serves as the control node for loop compensation. It connects to an external RC network that sets phase margin and bandwidth; typical values are RC = 2 kΩ and CC = 0.47 μF. This pin directly influences stability in both flyback and boost configurations, and improper compensation can cause oscillation or poor transient response in the LM2585SX-ADJ.
Can the LM2585SX-ADJ be used in a non-isolated boost configuration?
Yes, the LM2585SX-ADJ supports non-isolated boost topology with proper external components: a single inductor, Schottky diode, and output capacitor. The datasheet Figure 30 shows a working +5 V to +12 V boost example. However, output current must be externally limited to ≤3 A since the internal current limit does not protect the entire boost path during short-circuit conditions - a key constraint distinct from its flyback operation where the LM2585SX-ADJ provides full internal protection.
What is the minimum recommended copper area for the LM2585SX-ADJ thermal pad?
The LM2585SX-ADJ TO-263 package achieves its rated θJA = 35°C/W only when mounted on ≥1.0064 in² (7.4× the package footprint) of 1 oz. copper. Using less copper - such as 0.4896 in² - raises θJA to 56°C/W, severely limiting safe continuous current. For 3A operation at 60°C ambient, ≥1.0 in² copper is mandatory; insufficient copper area causes premature thermal shutdown and reduced reliability of the LM2585SX-ADJ.
How does the LM2585SX-ADJ handle short-circuit conditions in flyback mode?
In flyback configuration with standard transformers (e.g., T6 or T7), the LM2585SX-ADJ survives output shorts by reducing switching frequency to 25 kHz - extending off-time to fully discharge transformer energy before next cycle. This ensures zero-current turn-on and allows the internal 3.0 A current limit to protect the switch. Unlike boost mode, no external current limiter is required for main-output shorts, making the LM2585SX-ADJ inherently robust in properly designed flyback systems.
What resistor tolerance is recommended for programming VOUT on the LM2585SX-ADJ?
For stable output voltage across temperature and time, 1% metal film resistors are recommended for the FB divider (R1 and R2) in the LM2585SX-ADJ. The reference voltage has ±2.2 mV initial tolerance and ±1.5 mV line regulation; using 5% resistors introduces additional error that can exceed the ±4% total system tolerance. TI's application notes specify R2 between 1 kΩ and 5 kΩ - with R1 calculated as R2 × (VOUT/1.230 − 1) - to minimize bias current error and improve accuracy of the LM2585SX-ADJ.
LM2585SX-ADJ 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:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 4V
- Voltage - Input (Max):
- 40V
- Voltage - Output (Min/Fixed):
- 1.23V
- Voltage - Output (Max):
- 60V
- 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-ADJ FAQ
1.How can I place an order for LM2585SX-ADJ through Aetrix?
Please submit a Request for Quotation (RFQ) for LM2585SX-ADJ 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-ADJ reliable?
The price and inventory of LM2585SX-ADJ are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM2585SX-ADJ is usually 5 days.
3.What payment methods are accepted for LM2585SX-ADJ?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM2585SX-ADJ transactions.
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4.How is shipping managed for LM2585SX-ADJ?
LM2585SX-ADJ orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM2585SX-ADJ 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-ADJ?
For technical support, including LM2585SX-ADJ datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM2585SX-ADJ requirements.
6.How does Aetrix verify that LM2585SX-ADJ is sourced from the original manufacturer or authorized distributors?
All LM2585SX-ADJ 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-ADJ meets industry standards.
7.What is the process for return or replacement of LM2585SX-ADJ?
All LM2585SX-ADJ units undergo pre-shipment inspection (PSI). If there is an issue with LM2585SX-ADJ, 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-ADJ part is unused and in its original packaging.
Return procedure for LM2585SX-ADJ:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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