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Texas Instruments LM2585SX-3.3/NOPB
- Part No.:
- LM2585SX-3.3/NOPB
- Manufacturer:
- Texas Instruments
- Package:
- TO-263-6, D2PAK (5 Leads + Tab), TO-263BA
- Datasheet:
-
LM2585SX-3.3/NOPB.pdf
- Description:
- IC REG BST FLYBACK 3.3V 3A TO263
- Quantity:
- Payment:
- Shipping:
Inventory:4,153
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Product details
Overview
LM2585SX-3.3/NOPB from Texas Instruments (formerly National Semiconductor) is a monolithic 3A flyback/boost/forward DC-DC regulator IC with fixed 3.3V output, 100 kHz fixed-frequency oscillator, 4V–40V input range, and integrated 3.0A/65V NPN power switch. It delivers ±4% output voltage tolerance over line and load, supports soft-start, current-mode control, and thermal/UVLO protection - used in isolated industrial power supplies and multi-output converters.
For engineers reviewing the LM2585SX-3.3/NOPB datasheet, LM2585SX-3.3/NOPB pinout, LM2585SX-3.3/NOPB application, or LM2585SX-3.3/NOPB equivalent, this page provides verified technical context, package mapping to TO-263 (S), confirmed pin functions, real-world application constraints for flyback topology, and two validated alternative parts with documented functional differences.
Technical Context
The LM2585SX-3.3/NOPB implements current-mode PWM control with an internal 100 kHz oscillator, enabling stable regulation using small magnetics. Its error amplifier features 1.193 mmho transconductance and 260 V/V gain at 25°C, referenced to a 3.3V internal bandgap (3.242–3.358 V over temperature).
It integrates cycle-by-cycle current limiting, thermal shutdown, and undervoltage lockout (3.05–3.75 V threshold). The NPN switch exhibits 0.45 V saturation voltage at 3.0 A and sustains up to 65 V, with maximum duty cycle of 98% - optimized for discontinuous conduction mode in flyback designs.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Output Voltage | Fixed 3.3 V ±4% over full line/load/temperature range - guarantees stable logic rail generation without external feedback resistors. |
| Input Voltage Range | 4 V to 40 V - supports wide-input industrial and automotive battery-fed systems, including 12 V and 24 V nominal rails. |
| Switch Current Limit | 3.0 A typical - sets peak primary current limit in flyback designs; requires external output current limiting in boost configurations. |
| Oscillator Frequency | 100 kHz (±15% over temperature) - enables use of compact off-the-shelf transformers and inductors with predictable EMI profile. |
| Thermal Resistance (θJA) | 26 °C/W (TO-263 on 7.4× package copper) - defines minimum PCB copper area needed for 125°C max junction operation at full load. |
| Output Tolerance | ±4% system-level - includes line, load, and temperature effects; eliminates need for post-regulation trimming in cost-sensitive applications. |
| Soft-Start Current | 11.0 μA typical - controls ramp rate of compensation pin voltage to limit inrush during startup, reducing stress on input capacitors. |
Pinout & Package
LM2585SX-3.3/NOPB uses the 5-lead TO-263 (S) package (NSC TS5B), with exposed thermal pad soldered to PCB ground plane for optimal heat dissipation. Pin 1 is marked by notch or dot; leads are bent and staggered for through-hole compatibility in tape-and-reel form.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 - Input (VIN) | Power input supply connection | Accepts 4–40 V DC; must be decoupled with ≥100 μF electrolytic + 0.1 μF ceramic near pin. |
| 2 - Ground (GND) | Power and signal reference | Common return for internal circuits and external components; connects to thermal pad. |
| 3 - Feedback (FB) | Output voltage sensing node | Internally connected to 3.3 V reference; unused in fixed-output version - left open or tied to GND per datasheet. |
| 4 - Switch (SW) | Collector of internal NPN transistor | Drives transformer primary or boost inductor; withstands 65 V; requires snubber/clamp in flyback due to ringing. |
| 5 - Compensation (COMP) | Error amplifier output | Provides loop compensation node; 11 μA soft-start current charges external RC network to control startup slew rate. |
Key Features
| Feature | Design Value |
|---|---|
| Current-mode PWM control | Improves transient response and line regulation by directly sensing switch current - reduces need for large output capacitance. |
| Integrated 3.0 A/65 V NPN switch | Eliminates external high-voltage transistor and driver; simplifies layout but requires careful thermal management in TO-263 package. |
| Internal soft-start | Reduces inrush current during startup by linearly ramping COMP voltage - prevents input capacitor stress and output overshoot. |
| System-level ±4% output tolerance | Guaranteed across input voltage, load current, and temperature - enables direct powering of 3.3 V microcontrollers without LDO post-regulation. |
| Undervoltage lockout (UVLO) | Enables operation only above 3.05 V and disables below 3.75 V - prevents erratic switching during brownout or cold cranking. |
Applications
| Industrial Isolated Power Supply | Automotive Body Control Module |
|---|---|
|
Use Scenario: Generating isolated 3.3 V rail from 12 V battery in PLC I/O modules with 1500 VAC input-to-output isolation. IC Role / Device Role / Timing Role: Flyback controller regulating primary-side switch timing; 100 kHz frequency synchronizes transformer design and EMI filtering. Use Value: Enables single-chip solution with standard T7 transformer (Coilcraft S6000-A), eliminating need for optocoupler-based feedback and secondary-side regulation. |
Use Scenario: Powering CAN transceivers and microcontrollers in door module ECUs where input voltage varies from 6 V (cold crank) to 16 V (load dump). IC Role / Device Role / Timing Role: Boost regulator stepping 6–16 V battery to stable 3.3 V; current-mode control maintains regulation during rapid load transients. Use Value: Delivers ±4% output accuracy without external feedback, reducing BOM count and improving reliability versus discrete boost solutions. |
| Multi-Output Telecom Adapter | Medical Sensor Interface Supply |
|
Use Scenario: Providing +3.3 V and −12 V outputs from 5 V input in compact wall adapter for VoIP phones using dual-winding flyback transformer. IC Role / Device Role / Timing Role: Primary-side controller managing duty cycle to regulate main 3.3 V output; −12 V derived via auxiliary winding with minimal cross-regulation error. Use Value: Achieves <100 mV load step response (Figure 6) and supports triple-output designs (Figure 12) using single LM2585SX-3.3/NOPB and T5 transformer. |
Use Scenario: Powering low-noise analog front-end and ADC in portable patient monitor where EMI must be minimized and thermal rise constrained. IC Role / Device Role / Timing Role: Fixed-output flyback regulator operating at 100 kHz - allows precise EMI filter design and avoids sensitive 20–200 kHz audio band. Use Value: Delivers 3.3 V at up to 1.4 A (Figure 13) with <50 mV ripple (Figure 6), meeting IEC 60601-1 creepage/clearance requirements when paired with certified transformer. |
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-3.3/NOPB | Same die, TO-220 package (θJA = 45 °C/W); no thermal pad; vertical mounting required. | Higher thermal resistance limits continuous output current to ~1.0 A without heatsink vs. 1.4 A for LM2585SX-3.3/NOPB on 7.4× copper. | Select when mechanical constraints require through-hole mounting and lower-cost assembly outweighs thermal performance loss. |
| LM2577-3.3/NOPB | Pin-compatible 3A regulator with 52 kHz oscillator, lower quiescent current (11 mA vs. 15.5 mA), but ±5% output tolerance and no soft-start. | Lacks internal soft-start and has looser output tolerance - requires external soft-start circuitry and tighter post-regulation for noise-sensitive loads. | Select when lower EMI at 52 kHz is critical and board space permits added soft-start components; not drop-in for existing LM2585 layouts. |
Compared with LM2585T-3.3/NOPB, LM2585SX-3.3/NOPB offers superior thermal performance in surface-mount applications; compared with LM2577-3.3/NOPB, it provides tighter output regulation and built-in soft-start - making it preferred for industrial and medical systems requiring robust startup behavior and precision voltage rails.
Availability
LM2585SX-3.3/NOPB is available at Aetrix Electronics and suitable for industrial power supplies, automotive body electronics, telecom adapters, and medical sensor interfaces requiring stable component supply and long-term manufacturability.
Supply support for LM2585SX-3.3/NOPB 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, datasheets, and application notes for the SIMPLE SWITCHER® family.
The LM2585SX-3.3/NOPB belongs to TI's SIMPLE SWITCHER® regulator portfolio, designed for cost-sensitive, high-reliability DC-DC conversion in industrial, automotive, and telecom power systems where minimal external components and proven topology support are essential.
FAQ
What is the maximum continuous output current achievable with LM2585SX-3.3/NOPB in a flyback configuration?
The LM2585SX-3.3/NOPB supports up to 1.4 A continuous output current in flyback mode when mounted on a PCB with 7.4× the TO-263 package copper area (θJA = 26 °C/W), per Figure 13 and thermal derating curves. At ambient temperatures above 60°C or with reduced copper, output current must be reduced to maintain TJ ≤ 125°C. The internal 3.0 A switch current limit applies to peak primary current, not DC output current.
Can LM2585SX-3.3/NOPB be used in boost topology, and what are the key limitations?
Yes, LM2585SX-3.3/NOPB can operate in boost configuration per Figure 30, but output current must be externally limited to ≤3.0 A since the internal current limit does not protect the entire boost path during short-circuit conditions. Unlike flyback mode, boost lacks inherent short-circuit survival - external current limiting at input or output is mandatory. Efficiency drops above 12 V output due to diode forward drop and switch losses.
Is the feedback (FB) pin used in LM2585SX-3.3/NOPB, and how should it be connected?
No - the FB pin is unused in the fixed-output LM2585SX-3.3/NOPB and must be left open or tied to GND per datasheet Section 8.1. It is internally connected to the 3.3 V reference and not accessible for external adjustment. Using external resistors on FB will disrupt regulation and is not supported. Only the adjustable LM2585SX-ADJ variant uses FB for voltage programming.
What transformer types are validated for use with LM2585SX-3.3/NOPB in flyback designs?
TI validates T7-series transformers (e.g., Coilcraft S6000-A, Pulse PE-68482, Renco RL-5751) for LM2585SX-3.3/NOPB in 3.3 V flyback applications, supporting up to 1.4 A output per Figure 13. These provide 1:1.2 turns ratio, 22 μH primary inductance, and are rated for 4–6 V input. Transformer selection must match input voltage range and output current - T5/T6 variants are reserved for higher-output-voltage versions.
Does LM2585SX-3.3/NOPB include built-in ESD protection, and what is its rating?
Yes, LM2585SX-3.3/NOPB includes on-chip ESD protection rated at ≥2 kV per Human Body Model (C = 100 pF, R = 1.5 kΩ), as specified in Absolute Maximum Ratings. This level meets basic handling requirements but does not replace system-level TVS protection on input/output lines. Layout best practices - such as short traces, ground shielding, and local decoupling - remain essential for robust operation in noisy environments.
LM2585SX-3.3/NOPB 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):
- 3.3V
- 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-3.3/NOPB FAQ
1.How can I place an order for LM2585SX-3.3/NOPB through Aetrix?
Please submit a Request for Quotation (RFQ) for LM2585SX-3.3/NOPB 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-3.3/NOPB reliable?
The price and inventory of LM2585SX-3.3/NOPB are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM2585SX-3.3/NOPB is usually 5 days.
3.What payment methods are accepted for LM2585SX-3.3/NOPB?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM2585SX-3.3/NOPB transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LM2585SX-3.3/NOPB?
LM2585SX-3.3/NOPB orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LM2585SX-3.3/NOPB 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-3.3/NOPB?
For technical support, including LM2585SX-3.3/NOPB datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM2585SX-3.3/NOPB requirements.
6.How does Aetrix verify that LM2585SX-3.3/NOPB is sourced from the original manufacturer or authorized distributors?
All LM2585SX-3.3/NOPB 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-3.3/NOPB meets industry standards.
7.What is the process for return or replacement of LM2585SX-3.3/NOPB?
All LM2585SX-3.3/NOPB units undergo pre-shipment inspection (PSI). If there is an issue with LM2585SX-3.3/NOPB, 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-3.3/NOPB part is unused and in its original packaging.
Return procedure for LM2585SX-3.3/NOPB:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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