Texas Instruments LM2585T-ADJ/NOPB

Overview

LM2585T-ADJ/NOPB from Texas Instruments is a monolithic step-up (boost) and flyback DC-DC converter IC featuring a 3-A NPN output switch with 65-V standoff capability, 100-kHz fixed-frequency operation, current-mode control, and internal soft-start. It delivers adjustable output voltage (1.23 V to 40 V), supports 4 V to 40 V input range, and achieves ±4% system output voltage tolerance over line and load - used in industrial power supplies requiring compact, high-voltage boost conversion.

For engineers reviewing the LM2585T-ADJ/NOPB datasheet, LM2585T-ADJ/NOPB pinout, LM2585T-ADJ/NOPB application, or LM2585T-ADJ/NOPB equivalent, key selection criteria include its adjustable feedback reference (1.23 V), 3-A switch current limit, thermal shutdown protection, undervoltage lockout (3.3 V threshold), and compatibility with standard flyback transformers and boost inductors per TI's design guides.

Technical Context

The LM2585T-ADJ/NOPB implements current-mode PWM control using an internal 100-kHz oscillator and cycle-by-cycle peak current limiting. Its error amplifier compares a resistor-divided output voltage against a precise 1.230-V internal reference, generating a compensation signal that modulates switch on-time via a transconductance amplifier (3.2 mmho typical) and comparator.

Operation supports both boost and flyback topologies: in boost mode, energy transfers from input to output via series inductor; in flyback mode, it uses transformer-coupled isolation with primary-side switching and secondary-side rectification. The NPN switch sustains up to 65 V and saturates at ≤0.65 V at 3 A, with built-in thermal shutdown, UVLO, and current limiting protecting against fault conditions.

Key Specifications

Pinout & Package

LM2585T-ADJ/NOPB is packaged in a 5-pin TO-220 (NDH) with exposed tab for thermal dissipation (14.986 mm × 10.16 mm body). The tab is electrically connected to Pin 2 (Ground) and must be thermally coupled to a heatsink or copper pour.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar DC-DC controller applications.

Compared with LM2585T-ADJ/NOPB, LM2587T-ADJ/NOPB offers better EMI control at the cost of slightly higher supply current, while UC3845N provides frequency scalability and external switch freedom but demands more external circuitry and careful loop compensation.

Availability

LM2585T-ADJ/NOPB is available at Aetrix Electronics and suitable for industrial power supplies, telecom interface modules, automotive LED drivers, and isolated sensor power rails requiring stable component supply and long-term manufacturability.

Supply support for LM2585T-ADJ/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 is a global semiconductor company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and personal electronics markets.

The LM2585 series was designed as a cost-effective, easy-to-use monolithic solution for non-isolated boost and isolated flyback converters - targeting applications where minimal external components, thermal robustness, and ±4% output regulation are critical.

FAQ

What is the function of the Compensation pin (Pin 4) on the LM2585T-ADJ/NOPB?

The Compensation pin (Pin 4) is the output of the internal error amplifier in the LM2585T-ADJ/NOPB. It drives an external RC network to stabilize the feedback loop, ensuring phase margin and preventing oscillation. With a transconductance of 3.2 mmho (typ), this pin sources or sinks up to 260 μA, and its voltage swing ranges from 0.25 V to 2.8 V - directly influencing duty cycle and dynamic response in the LM2585T-ADJ/NOPB.

Can the LM2585T-ADJ/NOPB be used in a flyback configuration without an optocoupler?

Yes, the LM2585T-ADJ/NOPB supports primary-side sensing in flyback configurations using reflected voltage techniques, eliminating the need for an optocoupler. Its 1.23-V reference and current-mode control enable regulation based on primary-side feedback - confirmed in TI's Application Report SLVA053 and Figure 22–27 of the LM2585T-ADJ/NOPB datasheet. This reduces component count and improves reliability in the LM2585T-ADJ/NOPB design.

What is the maximum output current achievable with the LM2585T-ADJ/NOPB in boost mode?

In boost configuration, the LM2585T-ADJ/NOPB's output current is limited by external components and thermal design, not internal regulation. While the NPN switch handles 3 A peak, output current must be externally limited to ≤3 A to avoid switch overstress - per datasheet Section 6.1 Note (3). At 12 V output from 5 V input, practical continuous output is ~1.5 A with adequate heatsinking; the LM2585T-ADJ/NOPB datasheet specifies this constraint explicitly.

Does the LM2585T-ADJ/NOPB require a minimum load to maintain regulation?

No, the LM2585T-ADJ/NOPB does not require a minimum load for regulation. Its current-mode architecture and 100-kHz fixed frequency ensure stable operation down to zero load, as verified in typical characteristics (Figure 14, load step response) and electrical specifications across I_LOAD = 0.2 A to 0.8 A in flyback mode. Regulation remains within ±4% from no-load to full rated current in the LM2585T-ADJ/NOPB.

How does the LM2585T-ADJ/NOPB handle input voltage transients above 40 V?

The LM2585T-ADJ/NOPB has an absolute maximum input rating of 45 V, but recommended operation caps at 40 V. Transients exceeding 40 V - such as automotive load dump - risk damage unless clamped externally. TI recommends using a TVS diode (e.g., SMAJ33A) between VIN and GND, sized to absorb energy while holding voltage below 45 V. This protection strategy is documented in LM2585T-ADJ/NOPB application notes for automotive-grade implementations.