Monolithic Power Systems Inc. MP28257DD-LF-P

Overview

MP28257DD-LF-P from Monolithic Power Systems is a fully integrated, synchronous step-down DC/DC converter delivering up to 4A continuous output current with 4.2V–20V input range, 0.815V–13V adjustable output, and constant-on-time (COT) control for fast transient response in space-constrained power rails such as networking and distributed power systems.

For engineers reviewing the MP28257DD-LF-P datasheet, MP28257DD-LF-P pinout, MP28257DD-LF-P application, or MP28257DD-LF-P equivalent, key selection criteria include its 2mm×3mm QFN12 package, internal 120mΩ/50mΩ MOSFETs, programmable switching frequency, power-good indicator, and comprehensive protection suite (OCP, SCP, OVP, UVP, thermal shutdown).

Technical Context

The MP28257DD-LF-P employs constant-on-time (COT) control architecture with feed-forward input voltage compensation, enabling stable regulation across wide VIN and VOUT ranges without external compensation components. Its internal high-side and low-side MOSFETs eliminate external switch losses and simplify layout.

It integrates bootstrap circuitry (BST pin), soft-start/stop timing (~1ms), and open-drain power-good (PG) with 90% rising/85% falling thresholds and 500μs delay. Protection logic includes cycle-by-cycle over-current detection with 50μs hold-off, latch-off mode OCP/SCP, and non-latching UVLO (3.1V rising, 300mV hysteresis) and thermal shutdown (150°C, 25°C hysteresis).

Key Specifications

Pinout & Package

MP28257DD-LF-P is housed in a thermally enhanced, RoHS-compliant 2mm × 3mm QFN12 package with exposed thermal pad (Pin 11), optimized for high-power density and efficient PCB heat dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP28257DD-LF-P, MP2384GQ-Z offers higher current and wider input but requires more PCB area and lacks programmable frequency; RT6220HGJ6F saves space but sacrifices PG functionality and adds compensation complexity-making MP28257DD-LF-P optimal for balanced performance, protection, and layout simplicity in mid-density power rails.

Availability

MP28257DD-LF-P is available at Aetrix Electronics and suitable for networking equipment power rails, distributed telecom power systems, industrial PLC I/O modules, and embedded computing power applications requiring stable component supply, RoHS compliance, and long-term lifecycle support.

Supply support for MP28257DD-LF-P 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

Monolithic Power Systems (MPS) is a fabless semiconductor company specializing in high-performance analog and power ICs, with design centers in the US, China, and Taiwan, and global manufacturing partnerships.

The MP28257 belongs to MPS's high-efficiency, fast-transient synchronous buck converter product line, engineered for compact, thermally constrained power delivery in networking, telecom, and industrial embedded systems where reliability and minimal external components are critical.

FAQ

What is the recommended input capacitor configuration for MP28257DD-LF-P?

A minimum 22µF X5R/X7R ceramic capacitor rated for ≥25V should be placed directly at the IN pin with short, wide traces and multiple vias to ground. For systems with high input ripple current, add a second 10µF capacitor in parallel. Total RMS current rating must exceed half the maximum output current (e.g., ≥2A for 4A load) to prevent overheating and capacitance loss.

Does MP28257DD-LF-P support ceramic output capacitors without external compensation?

Yes-MP28257DD-LF-P is explicitly designed to operate stably with low-ESR ceramic output capacitors. However, external ramp compensation (R4/C4) is required for PWM-mode stability when using ceramics; the datasheet provides equations and design guidelines to size R4 and C4 based on switching frequency, inductance, and output voltage.

How does the constant-on-time (COT) control affect light-load efficiency?

COT control enables automatic frequency reduction in light-load conditions, transitioning into skip mode where the inductor current drops to zero and the LS-FET enters high-Z state. This reduces switching losses significantly-achieving >85% efficiency at 10mA load-while maintaining regulation without requiring external control signals.

What is the function of the BST pin and how should it be implemented?

The BST pin supplies the floating gate drive voltage for the internal high-side MOSFET. It must be connected to SW via a 0.1µF ceramic capacitor (X5R/X7R, 10V rating). Improper BST capacitor placement or value causes high-side driver failure, leading to no output or thermal shutdown. The capacitor must be placed adjacent to the BST and SW pins with minimal trace length.

Can MP28257DD-LF-P be used in new designs despite the "Not Recommended for New Designs" note?

No-Monolithic Power Systems explicitly states "NOT RECOMMENDED FOR NEW DESIGNS" and directs users to MP2384. While MP28257DD-LF-P remains functional and supported for existing production, Aetrix Electronics advises new designs to evaluate MP2384GQ-Z for improved specs, active lifecycle status, and long-term supply assurance.

What is the thermal performance limit for continuous 4A operation?

At TA = 85°C with a 4-layer PCB per JESD51-7, the MP28257DD-LF-P can sustain 4A output continuously if the PCB includes a 200mm² copper pour connected to the exposed thermal pad (Pin 11) and ≥4 thermal vias. Junction temperature remains below 125°C under these conditions; exceeding this requires derating or forced airflow.

How does the power-good (PG) signal behave during startup and fault conditions?

PG goes high 500μs after FB reaches ≥90% of 815mV (i.e., ≥734mV), indicating valid regulation. During faults-such as OVP (FB > 1019mV), UVP (FB < 408mV), or thermal shutdown-PG pulls low within microseconds. PG remains low until a full power cycle resets protection latches, ensuring unambiguous system-level fault indication.