Texas Instruments LM2585T-12

Overview

LM2585T-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 LM2585T-12 datasheet, LM2585T-12 pinout, LM2585T-12 application, or LM2585T-12 equivalent, key selection criteria include its TO-220 package thermal performance (θ_JA = 65°C/W unheatsinked), current-mode control architecture, soft-start function, and compatibility with standard flyback transformers like Coilcraft T7 and Renco RL-5751.

Technical Context

The LM2585T-12 implements current-mode PWM control with an internal 100 kHz oscillator, enabling stable regulation using small magnetics. Its error amplifier compares feedback voltage against a trimmed 12.0V reference (V_REF = 11.79–12.24V), generating a compensation signal that modulates peak switch current via cycle-by-cycle current limiting.

Protection includes undervoltage lockout (3.05–3.75V), thermal shutdown, and internal current limit (4.0–7.0A typical). The NPN switch exhibits V_SAT ≤ 0.65V at 3.0A and sustains up to 65V, supporting flyback topologies where V_SW(OFF) = V_IN(MAX) + (V_OUT + V_F)/N.

Key Specifications

Pinout & Package

LM2585T-12 is housed in a 5-lead TO-220 package (NSC package T05D) with bent, staggered leads. The case is electrically connected to Pin 2 (Ground), requiring isolation if mounting to heatsink.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar flyback/boost regulator applications.

Compared with LM2585S-12 and LM2577-12, the LM2585T-12 uniquely supports both flyback and boost topologies in a through-hole TO-220 package, offering design flexibility for isolated and non-isolated 12V supplies without layout change penalties-critical for industrial field-serviceable equipment.

Availability

LM2585T-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 LM2585T-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 legacy SIMPLE SWITCHER® product lines with full datasheet, simulation model, and application support.

The LM2585 series was designed specifically for cost-effective, low-component-count flyback and boost DC-DC conversion in industrial, telecom, and automotive power systems-emphasizing ruggedness, thermal reliability, and ease of transformer selection.

FAQ

What is the maximum input voltage the LM2585T-12 can handle?

The LM2585T-12 supports an absolute maximum input voltage of 45V, but its recommended operating range is 4V to 40V. Exceeding 40V risks violating the 65V switch standoff rating under transient conditions, especially in flyback configurations where reflected voltages add to input. Always verify V_SW(OFF) = V_IN(MAX) + (V_OUT + V_F)/N remains below 65V using the selected transformer turns ratio.

Does the LM2585T-12 require external components to set the output voltage?

No. The LM2585T-12 has a factory-trimmed 12.0V reference internally connected to the Feedback pin, eliminating external resistor dividers. This differs from the LM2585T-ADJ version, which requires R1/R2 to program V_OUT. For LM2585T-12, the Feedback pin connects directly to the output via a short trace or optional RC filter for noise immunity.

Can the LM2585T-12 be used in a non-isolated boost configuration?

Yes. The LM2585T-12 functions as a boost regulator per Figure 30 in the datasheet, delivering 12V from inputs as low as 4V. However, output current must be externally limited to ≤3A since the internal current limit does not protect the entire boost path during short circuits. Use input current limiting or foldback protection in safety-critical designs.

What thermal considerations apply to the LM2585T-12 in TO-220 package?

The LM2585T-12 in TO-220 has θ_JA = 65°C/W with minimal copper and 45°C/W with 4 in² copper. At 1.5W dissipation and 25°C ambient, junction temperature reaches ~120°C-near the 125°C max operating limit. A heatsink or ≥2 in² thermal pad is mandatory for continuous 3A output. Derate output current above 70°C ambient per Figure 10 thermal curves.

Which transformers are validated for use with the LM2585T-12 in flyback mode?

The LM2585T-12 is validated with Coilcraft T7 (S6000-A, S6057-A), Renco RL-5751, Pulse PE-68482, and Schott 26606 transformers per Figure 13. These provide 1:1.2 or 1:1.15 turns ratios optimized for 12V output at 0.2–0.8A load. Using non-listed transformers may cause instability or exceed V_SW limits due to leakage inductance or saturation.