Texas Instruments LM2587S-3.3

Overview

LM2587S-3.3 from Texas Instruments is a monolithic 5A flyback/boost switching regulator IC with fixed 3.3V output, integrated 5.0A/65V NPN power switch, 100 kHz fixed-frequency oscillator, and internal soft-start. It delivers ±4% system output voltage tolerance over line and load, supports 4V–40V input, and is used in isolated DC-DC converters for industrial power supplies and embedded systems requiring compact, low-component-count 3.3V generation.

For engineers reviewing the LM2587S-3.3 datasheet, LM2587S-3.3 pinout, LM2587S-3.3 application, or LM2587S-3.3 equivalent, key selection criteria include its 3.3V fixed output, 5A switch current rating, TO-263 (S) package thermal performance, and compatibility with standard flyback transformers such as Coilcraft Q4434-B and Schott 67141450.

Technical Context

The LM2587S-3.3 implements current-mode control with cycle-by-cycle current limiting, enabling stable regulation under transient load and line variations. Its error amplifier features 3.3V reference voltage (VREF), 1.193 mmho transconductance (GM), and 260 V/V open-loop gain (AVOL), referenced to the feedback pin.

Operation relies on internal soft-start (11.0 μA ISS), undervoltage lockout (3.30V threshold), and thermal shutdown. The 100 kHz oscillator drives the NPN switch with up to 98% duty cycle, supporting flyback, boost, and forward topologies without external frequency programming.

Key Specifications

Pinout & Package

LM2587S-3.3 is housed in a 5-lead TO-263 (S) surface-mount package with exposed thermal pad. Pin 1 is Input (VIN), Pin 2 is Ground (GND), Pin 3 is Feedback (FB), Pin 4 is Output Switch (SW), and Pin 5 is Compensation (COMP). The exposed pad must be soldered to PCB copper for thermal management.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2587T-3.3, the LM2587S-3.3 offers superior thermal performance in SMT layouts due to lower θJA (26°C/W vs 45°C/W), while LM2577S-3.3 trades switching frequency, protection features, and output current capability for reduced system cost in non-critical applications.

Availability

LM2587S-3.3 is available at Aetrix Electronics and suitable for industrial PLC power supplies, automotive body control modules, medical patient monitors, and telecom remote terminal units requiring stable component supply and long-term production continuity.

Supply support for LM2587S-3.3 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 leader specializing in analog, embedded processing, and power management technologies, with decades of expertise in switching regulator design and manufacturing.

The LM2587S-3.3 belongs to TI's SIMPLE SWITCHER® family-engineered for ease-of-use in isolated and non-isolated DC-DC conversion, targeting cost-sensitive, high-reliability industrial and automotive power applications.

FAQ

What is the maximum output current capability of the LM2587S-3.3 in flyback configuration?

The LM2587S-3.3 supports up to 1.75A output current in flyback configuration under specified conditions (VIN = 4V–12V, TJ ≤ 125°C), as guaranteed by system-level testing in the datasheet. This assumes proper transformer selection (e.g., Coilcraft Q4434-B), adequate PCB copper area for thermal dissipation, and adherence to the recommended layout guidelines for the TO-263 package. Exceeding this current risks thermal shutdown or degraded regulation.

Does the LM2587S-3.3 require external feedback resistors to set the output voltage?

No, the LM2587S-3.3 does not require external feedback resistors because it integrates a factory-trimmed 3.3V reference directly tied to the feedback pin. Unlike the adjustable LM2587-ADJ variant, the -3.3 version uses internal resistor networks to fix the output at 3.3V, simplifying design and eliminating resistor tolerance and temperature drift concerns. The FB pin remains accessible for optional monitoring or loop compensation tuning.

What is the purpose of the COMP pin on the LM2587S-3.3, and how should it be configured?

On the LM2587S-3.3, the COMP pin is the output of the internal error amplifier and serves as the compensation node for stabilizing the control loop. It must be connected to an RC network (e.g., 2 kΩ resistor and 0.47 μF capacitor as shown in Figure 6 of the datasheet) between COMP and GND. This network sets dominant pole frequency and phase margin-critical for preventing oscillation and ensuring step-load stability in flyback or boost configurations.

Can the LM2587S-3.3 be used in boost topology, and what are the key design constraints?

Yes, the LM2587S-3.3 can be used in boost topology, but output current must be externally limited to ≤5A since internal current limiting does not protect the entire boost path during short-circuit conditions. Designers must ensure the inductor (e.g., Renco RL-5472-5) and output diode (e.g., 1N5820) are rated for peak currents and reverse voltages exceeding worst-case conditions. Efficiency drops significantly below 4V input, and thermal management becomes critical above 1A output in boost mode.

How does the undervoltage lockout (UVLO) function on the LM2587S-3.3 affect system startup behavior?

The LM2587S-3.3 incorporates a 3.30V UVLO threshold with ~0.45V hysteresis, meaning the device remains disabled until VIN rises above 3.75V and stays active down to 3.30V. This prevents erratic switching and output instability during brown-out conditions. Startup is synchronized with internal soft-start, so the COMP pin ramps linearly over ~10 ms, ensuring controlled rise of output voltage and limiting in-rush current into output capacitors-critical for reliable operation in battery-powered systems.