Texas Instruments LMR51420XDDCR

Overview

LMR51420XDDCR from Texas Instruments is a synchronous buck DC-DC converter IC designed for industrial power conditioning, delivering up to 2 A continuous output current from a 4.5 V to 36 V input supply, operating at a fixed 500-kHz switching frequency in PFM mode, and housed in a 6-pin SOT-23 (DBV) package for compact board space.

For engineers reviewing the LMR51420XDDCR datasheet, LMR51420XDDCR pinout, LMR51420XDDCR application, or LMR51420XDDCR equivalent, key selection considerations include its 70-ns minimum on-time, ±1.5% reference voltage tolerance, precision enable with adjustable UVLO, internal compensation, and support for prebiased startup in rugged wide-VIN systems.

Technical Context

The LMR51420XDDCR employs fixed-frequency peak-current mode control with internal slope compensation and an integrated error amplifier. It features cycle-by-cycle current limiting, hiccup-mode short-circuit protection, and thermal shutdown at 163°C with 22°C hysteresis.

It operates in PFM mode at light load for high efficiency and supports frequency foldback down to ~133 kHz when minimum on-time (70 ns) or off-time (150 ns) limits are reached-enabling regulation across its full 4.5–36 V input range while maintaining 98% maximum duty cycle capability.

Key Specifications

Pinout & Package

LMR51420XDDCR is packaged in a 6-pin SOT-23 (DBV) case measuring 2.90 mm × 1.60 mm, optimized for thermal performance on 2-layer PCBs (R_θJA ≈ 80°C/W) and minimal layout area.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LMR51420XDDCR, TPS54202DRCT offers legacy compatibility but sacrifices 36 V operation and extended temperature capability, while LMR51420XFDDCR delivers identical robustness with deterministic FPWM behavior-making it ideal for noise-sensitive or time-critical subsystems.

Availability

LMR51420XDDCR is available at Aetrix Electronics and suitable for industrial motor drives, building automation sensors, appliance control boards, and general-purpose wide-VIN power supplies requiring stable component supply across long production lifecycles.

Supply support for LMR51420XDDCR 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 industrial and automotive power solutions.

The LMR51420 series belongs to TI's SIMPLE SWITCHER® portfolio-designed specifically for ease-of-use, ruggedness, and rapid deployment in cost-sensitive industrial power applications where wide input range and thermal resilience are critical.

FAQ

What is the switching frequency of the LMR51420XDDCR?

The LMR51420XDDCR operates at a fixed 500 kHz switching frequency in PFM mode. This frequency is factory-trimmed and not user-adjustable. It enables compact magnetics and predictable EMI behavior while supporting frequency foldback below 500 kHz under extreme duty-cycle conditions (e.g., very low VIN or very high step-down ratio). The LMR51420XDDCR does not support 1.1 MHz operation-that variant is designated LMR51420YDDCR.

Does the LMR51420XDDCR support prebiased output startup?

Yes, the LMR51420XDDCR supports start-up with a prebiased output. This feature prevents reverse current flow when the output voltage is already present (e.g., from backup supplies or hot-swap conditions) before input power is applied. During prebias start, the device controls high-side and low-side FETs to ramp the output safely without damaging external components or causing system instability-verified per datasheet Section 8.3.1 and electrical characteristics tables.

What is the purpose of the CB pin on the LMR51420XDDCR?

The CB (bootstrap capacitor) pin on the LMR51420XDDCR provides the gate drive voltage for the internal high-side NMOS FET. A 100-nF ceramic capacitor must be connected between CB and SW pins. During low-side conduction, this capacitor charges from the internal LDO; during high-side conduction, it supplies the boosted voltage needed to fully enhance the high-side FET. Using an X7R/X5R dielectric capacitor rated ≥16 V ensures stable bootstrap operation across temperature and line/load variations.

Can the LMR51420XDDCR replace the TPS54202 in an existing design?

The LMR51420XDDCR is pin-to-pin compatible with the TPS54202 and TPS54302 per TI documentation, sharing the same 6-pin SOT-23 (DBV) footprint and pinout. However, the LMR51420XDDCR extends input voltage to 36 V (vs. 28 V) and junction temperature to 150°C (vs. 125°C), offering greater design margin. Layout reuse is possible, but verify thermal performance and input transient handling-especially if operating near 28–36 V-since internal FET R_DS(on) and protection thresholds differ.

What output voltage accuracy can be expected from the LMR51420XDDCR?

The LMR51420XDDCR achieves ±1.5% reference voltage tolerance (0.6 V ±9 mV) over –40°C to +150°C, contributing directly to output voltage accuracy. Total output regulation error-including FB resistor divider tolerance, temperature drift, and load/line effects-is typically ±2.5% for PFM operation and ±1.5% for FPWM operation (per Section 7.6). Using 1% metal-film resistors with low TCR in the feedback network minimizes additional error and ensures compliance with most industrial MCU and sensor supply requirements.