Texas Instruments LM2598SX-3.3

Overview

LM2598SX-3.3 from Texas Instruments is a monolithic 150 kHz step-down (buck) switching voltage regulator IC delivering a fixed 3.3 V output at up to 1 A, with ±4% output voltage tolerance over line and load, input voltage range up to 40 V, and integrated thermal shutdown and current limiting. It serves as a high-efficiency DC-DC power conversion stage in embedded power supplies.

For engineers reviewing the LM2598SX-3.3 datasheet, LM2598SX-3.3 pinout, LM2598SX-3.3 application, or LM2598SX-3.3 equivalent, key selection considerations include its fixed 3.3 V output, 7-pin DDPAK surface-mount package, 150 kHz oscillator, soft-start/shutdown control, and dropout flag functionality - all critical for compact, thermally constrained industrial and automotive power designs.

Technical Context

The LM2598SX-3.3 implements a current-mode PWM buck topology with internal 150 kHz oscillator, two-stage current limit protection, and built-in soft-start via the SS/SD pin. Its feedback loop is internally compensated and references a stable bandgap, eliminating external compensation components.

It integrates a high-side N-channel MOSFET switch, error amplifier, oscillator, soft-start timer, thermal shutdown circuitry, and an open-collector FLAG output that asserts low when output drops below 92–98% of nominal. The device operates across −25°C to +125°C junction temperature and supports input voltages from 4.5 V to 40 V.

Key Specifications

Pinout & Package

LM2598SX-3.3 is housed in a 7-lead DDPAK (KTT/KTW0007B) surface-mount package with exposed thermal pad for enhanced heat dissipation. The package is lead-free and RoHS-compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2596SX-3.3, LM2598SX-3.3 adds essential system-level supervision (FLAG/DELAY) and ultra-low shutdown IQ; versus MP1584EN-LF-Z, it trades higher frequency for simpler layout, integrated compensation, and robust fault signaling - making it optimal for reliability-critical industrial power rails.

Availability

LM2598SX-3.3 is available at Aetrix Electronics and suitable for industrial PLCs, automotive body control units, medical point-of-care devices, and industrial Ethernet gateways requiring stable component supply, long-term lifecycle support, and guaranteed traceability.

Supply support for LM2598SX-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 high-reliability power conversion ICs.

The LM2598 series was designed specifically for cost-sensitive, thermally constrained industrial and automotive DC-DC applications where simplicity, fault visibility, and long-term manufacturability are prioritized over ultra-high frequency or ultra-miniaturization.

FAQ

What is the maximum input voltage rating for LM2598SX-3.3?

The absolute maximum input voltage for LM2598SX-3.3 is 45 V, but the recommended operating range is 4.5 V to 40 V per the datasheet. Exceeding 40 V may compromise long-term reliability and thermal margin. The device's internal current limit and thermal shutdown protect against transient overvoltage events, but sustained operation above 40 V is not specified or guaranteed. Always verify input transient clamping in your application when using near-maximum inputs.

Does LM2598SX-3.3 require external compensation components?

No, LM2598SX-3.3 does not require external compensation components. It features fully internal frequency compensation optimized for standard buck configurations with 68 μH inductors and 120 μF output capacitors. This simplifies design, reduces BOM count, and improves production yield. The fixed-output version uses an internal resistor divider, eliminating feedback network tuning - unlike the adjustable LM2598-ADJ variant, which requires external resistors and optional feedforward compensation.

How does the FLAG pin on LM2598SX-3.3 function in practice?

The FLAG pin on LM2598SX-3.3 is an open-drain output that pulls low when the regulated 3.3 V output drops below 92–98% of nominal (i.e., <3.04 V). Its assertion is delayed by an external capacitor on the DELAY pin (typically 0.1 μF for ~10 ms), preventing false triggers during brief load transients. In normal operation, FLAG remains high-impedance; a pull-up resistor (e.g., 4.7 kΩ to 3.3 V) is required. This signal directly interfaces with microcontroller GPIOs or supervisor ICs for real-time power health monitoring.

Can LM2598SX-3.3 operate without a heatsink in a 1 A application?

Yes, LM2598SX-3.3 can operate without an external heatsink at 1 A when mounted on a double-sided PCB with ≥3 in² copper area on the component side and ≥16 in² on the opposite side (θJA = 20°C/W), provided ambient temperature stays ≤50°C. At higher ambient or with reduced copper area (e.g., single-sided board, θJA = 50°C/W), thermal derating applies: output current must be reduced to ~0.5 A to maintain TJ <125°C. The DDPAK package's exposed thermal pad must be soldered to the PCB copper for effective conduction.

What inductor value is recommended for LM2598SX-3.3 at 12 V input and 1 A load?

For LM2598SX-3.3 operating at VIN = 12 V and IOUT = 1 A, the recommended inductor is 68 μH (inductor code L30), as specified in TI's Figure 26 and Table 2. This value balances peak-to-peak inductor ripple current (~30% of IOUT), core saturation margin, and physical size. Standard through-hole or surface-mount variants (e.g., Coilcraft MSS7341-683, Bourns SRP1265-683) are validated for use. Inductor DCR should be ≤150 mΩ to minimize conduction losses and preserve efficiency.