Texas Instruments LM25018SDX/NOPB

Overview

LM25018SDX/NOPB from Texas Instruments is a 48-V, 325-mA synchronous buck/Fly-Buck™ regulator with integrated high-side and low-side N-channel MOSFETs, constant on-time (COT) control, 7.5–48 V input range, and 1.225 V ±2% feedback reference. It delivers isolated bias power in telecom systems and industrial equipment without requiring external Schottky diodes.

For engineers reviewing the LM25018SDX/NOPB datasheet, LM25018SDX/NOPB pinout, LM25018SDX/NOPB application, or LM25018SDX/NOPB equivalent, key selection criteria include its COT architecture enabling no loop compensation, intelligent peak current limit (390–750 mA), adjustable switching frequency up to 1 MHz via RON, and dual-package availability (WSON-8 and SO PowerPAD-8) for thermal optimization.

Technical Context

The LM25018SDX/NOPB implements a constant on-time control scheme where on-time varies inversely with VIN-ensuring nearly constant operating frequency across 7.5–48 V input. Its internal 7.6-V VCC regulator powers gate drivers and logic, with UVLO hysteresis programmable via external resistor divider on UVLO pin.

It features an intelligent current-limit off-timer whose duration depends on FB voltage and VIN (e.g., 16 µs at FB = 0 V, VIN = 48 V), enabling robust short-circuit protection without foldback. The synchronous rectifier operates in continuous conduction mode (CCM) at all loads, with no diode emulation.

Key Specifications

Pinout & Package

LM25018SDX/NOPB is packaged in an 8-pin WSON (4.00 mm × 4.00 mm) with exposed thermal pad, optimized for compact layouts and enhanced thermal dissipation in high-density industrial PCBs.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous buck regulator applications.

Compared with LM5164QDDARQ1 and TPS54202DDCR, the LM25018SDX/NOPB uniquely balances 48-V input capability, Fly-Buck™ isolation support, and zero-compensation COT control in a thermally enhanced 8-pin WSON-making it optimal for industrial and telecom auxiliary power where input voltage range and topology flexibility outweigh raw current rating.

Availability

LM25018SDX/NOPB is available at Aetrix Electronics and suitable for industrial equipment power supplies, smart power meter bias rails, and telecom line card applications requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LM25018SDX/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 leader designing analog, embedded processing, and connectivity technologies for industrial, automotive, and communications markets.

The LM25018SDX/NOPB belongs to TI's high-voltage DC/DC regulator product line, engineered specifically for efficient, compact, and reliable step-down conversion from 7.5–48 V input rails in space- and thermal-constrained industrial systems.

FAQ

What is the recommended minimum on-time for LM25018SDX/NOPB and how is it set?

The LM25018SDX/NOPB requires a minimum on-time ≥100 ns at maximum input voltage (48 V) for stable operation. This is set by selecting the RON resistor value per the equation T_ON = (10⁻¹⁰ × R_ON) / V_IN. For example, with R_ON = 100 kΩ at 48 V, T_ON ≈ 208 ns-well above the 100 ns threshold. Using LM25018SDX/NOPB with insufficient RON risks pulse-skipping and regulation instability.

Does LM25018SDX/NOPB support Fly-Buck™ topology and what design considerations apply?

Yes, LM25018SDX/NOPB explicitly supports Fly-Buck™ isolated DC/DC conversion using a coupled inductor. Critical design considerations include ensuring ≥25 mV ripple at the FB pin (achieved via output capacitor ESR or added RC network), maintaining tight coupling (k > 0.98) in the transformer, and verifying that the secondary winding voltage does not exceed absolute maximum ratings on BST/SW pins. The LM25018SDX/NOPB datasheet provides validated Fly-Buck™ reference designs confirming this capability.

What is the function of the UVLO pin on LM25018SDX/NOPB and how is it configured?

The UVLO pin on LM25018SDX/NOPB enables programmable input undervoltage lockout with independently adjustable threshold and hysteresis. It is configured using a resistor divider from VIN to RTN, where the threshold (1.225 V typ) and hysteresis (set by internal 20-μA current source × R_UV2) determine startup and shutdown points. Pulling UVLO below 0.66 V forces LM25018SDX/NOPB into low-current shutdown mode-enabling remote enable/disable functionality.

Can LM25018SDX/NOPB operate without an external bootstrap capacitor?

No, LM25018SDX/NOPB requires an external 0.01-μF ceramic capacitor between BST and SW pins. This capacitor supplies gate drive voltage to the high-side MOSFET during its on-time. During the off-time, the internal diode recharges the BST capacitor from the VCC rail. Omitting this capacitor will prevent proper high-side switching, causing immediate functional failure and potential damage to the LM25018SDX/NOPB.

What thermal performance can be expected from LM25018SDX/NOPB in WSON-8 package?

In the WSON-8 package, LM25018SDX/NOPB achieves θ_JA = 41.3°C/W (junction-to-ambient) and θ_JC(bot) = 3.2°C/W (junction-to-case bottom) when mounted on a 2-layer PCB with 1-in² 2-oz copper thermal pad. With proper thermal vias to inner ground planes, typical junction temperature rise is ≤35°C at 325 mA output and 24 V input-well within the 125°C max operating limit. The exposed pad must be soldered to RTN for these values to hold.