Texas Instruments LM2599S-ADJ

Overview

LM2599S-ADJ from Texas Instruments is a monolithic 150-kHz nonsynchronous step-down DC-DC converter delivering up to 3 A output current, supporting adjustable output voltage from 1.2 V to 37 V (±4% tolerance), with input voltage range up to 40 V and internal thermal/current protection. It serves as a primary buck regulator in industrial power supplies requiring stable, high-efficiency conversion.

For engineers reviewing the LM2599S-ADJ datasheet, LM2599S-ADJ pinout, LM2599S-ADJ application, or LM2599S-ADJ equivalent, key selection criteria include its 3-A continuous output capability, ±4% output voltage accuracy over line/load/temperature, 150-kHz fixed-frequency operation enabling compact magnetics, shutdown/soft-start control, and out-of-regulation error flag for system monitoring.

Technical Context

The LM2599S-ADJ implements a voltage-mode controlled buck topology with internal 150-kHz oscillator, integrated 3-A N-channel DMOS switch, and built-in soft-start and shutdown logic. Its feedback loop uses a precision 1.23-V reference and low-bias-current (≤50 nA) feedback amplifier to maintain regulation across wide input (4.5–40 V) and output (1.2–37 V) ranges.

Functional modes include normal regulation, shutdown (80 μA standby current), and fault response via thermal shutdown and two-stage current limiting. The error flag output provides open-collector indication of >5% output undervoltage with programmable delay via external capacitor on the DELAY pin.

Key Specifications

Pinout & Package

LM2599S-ADJ is available in 7-pin TO-220 (NDZ) and 7-pin TO-263 (KTW) packages. Both variants share identical pin functions and numbering. The exposed tab (pins 4 and 7 in TO-220; tab in TO-263) is electrically connected to GND and serves as primary thermal path.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator applications.

Compared with LM2678-ADJ and TPS54302DDAR, LM2599S-ADJ uniquely balances wide 4.5–40 V input compatibility, 3-A continuous output, and proven ruggedness in harsh environments-making it optimal for industrial and automotive pre-regulation where input voltage variability and fault resilience are paramount.

Availability

LM2599S-ADJ is available at Aetrix Electronics and suitable for industrial power supplies, automotive aftermarket electronics, and programmable lab equipment requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LM2599S-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 is a global semiconductor leader specializing in analog, embedded processing, and power management technologies, with decades of expertise in high-reliability power conversion ICs.

The LM2599 series belongs to TI's SIMPLE SWITCHER® portfolio, designed specifically for ease-of-use in non-isolated DC-DC buck applications where minimal external components, robust protection, and predictable performance are essential.

FAQ

What is the maximum input voltage rating for LM2599S-ADJ?

The absolute maximum input voltage for LM2599S-ADJ is 45 V, but the recommended operating range is 4.5 V to 40 V per the datasheet. Exceeding 40 V continuously risks violating safe operating area limits, especially under high ambient temperatures or heavy load. The device includes internal clamping and thermal shutdown, but sustained operation above 40 V is not guaranteed and may reduce reliability. Always refer to Section 7.1 Absolute Maximum Ratings and Section 7.3 Recommended Operating Conditions in the official LM2599S-ADJ datasheet for design margins.

How do I calculate the output voltage setting for LM2599S-ADJ?

The output voltage of LM2599S-ADJ is set by a resistor divider from VOUT to GND and from the divider junction to the FB pin. Use the formula VOUT = 1.23 V × (1 + R1/R2), where R2 connects FB to GND and R1 connects VOUT to FB. For example, to achieve 12 V output, select R2 = 1.2 kΩ and R1 ≈ 10.5 kΩ (standard 1% value). The feedback bias current is ≤50 nA, so resistor values should stay below 200 kΩ total to avoid significant divider error. TI's Webench® Designer tool validates these calculations using actual LM2599S-ADJ models and thermal constraints.

Does LM2599S-ADJ require an external catch diode, and what type is recommended?

Yes, LM2599S-ADJ requires an external catch diode due to its nonsynchronous buck architecture. A Schottky diode rated for ≥3 A average current and ≥45 V PIV is recommended-such as the SB560 (5 A, 60 V) or MBR360 (3 A, 60 V). Schottky types minimize forward voltage drop (typically 0.4–0.5 V), improving efficiency and reducing thermal stress. Fast recovery diodes like UF5408 may be used if Schottky parts are unavailable, but expect ~0.2%–0.5% efficiency loss and higher diode temperature rise at full load.

Can LM2599S-ADJ be used in an inverting (positive-to-negative) configuration?

Yes, LM2599S-ADJ supports inverting regulator topologies as documented in TI's LM2599 datasheet Figure 21. In this configuration, the GND pin is referenced to the negative output, and the FB pin is tied to system ground, allowing regulation of −VOUT. A Schottky diode (e.g., SB560) and 33-μH inductor are recommended. Startup inrush current can reach ~4.5 A briefly, so soft-start via the SD/SS pin is strongly advised. Input-to-output voltage sum must remain ≤40 V-for example, 20 V input yields up to −20 V output. This mode is validated for low-noise analog biasing in POS terminals and instrumentation.

What thermal considerations apply to LM2599S-ADJ in TO-220 and TO-263 packages?

LM2599S-ADJ in TO-220 (NDZ) has RθJA ≈ 50°C/W with minimal copper; adding a 1-in² 1-oz copper pad reduces it to ~30°C/W. In TO-263 (KTW), RθJA drops to ~20°C/W with 3-in² copper on one side and 16-in² on the other. The junction-to-case (top) thermal resistance is 2°C/W for both packages, making heatsink attachment to the exposed tab highly effective. At 3-A load and 12-V input → 5-V output, dissipation is ~2.1 W-so with 20°C/W and 25°C ambient, junction temperature reaches ~67°C, well within the 125°C max operating limit. Always verify layout per Section 11 of the datasheet.