Monolithic Power Systems Inc. MP3908DK-LF-P

Overview

MP3908DK-LF-P from Monolithic Power Systems is a current-mode PWM controller with synchronous secondary gate drive, designed for high-efficiency boost, SEPIC, flyback, and forward topologies. It delivers 250 kHz constant-frequency operation, 10 V gate driver compliance, programmable dead-time control, and lossless current sensing (≤28 V) - enabling >10 A MOSFET drive in PoE PD and telecom isolated power supplies.

For engineers reviewing the MP3908DK-LF-P datasheet, MP3908DK-LF-P pinout, MP3908DK-LF-P application, or MP3908DK-LF-P equivalent, key selection criteria include its 0.818 V feedback reference, 270 µA typical operating current, 50 ns minimum on-time, cycle-by-cycle current limiting, and resistor-programmable RDELAY timing for synchronous rectifier overlap control.

Technical Context

The MP3908DK-LF-P implements a peak-current-mode control architecture with an internal 0.818 V reference, transconductance error amplifier (0.32 mA/V typ), and slope compensation to ensure loop stability across wide duty cycles. Its dual gate drivers provide matched sourcing/sinking impedances (16 Ω/5.0 Ω) for main and synchronous MOSFETs, supporting precise timing coordination.

It integrates UVLO (4.7 V turn-on), soft-start via CSS pin (5 µA charging current), and thermal shutdown at 150 °C. The ISENSE pin accepts direct drain-sense up to 28 V, eliminating external sense resistors in low-voltage boost applications - reducing conduction loss and component count.

Key Specifications

Pinout & Package

The MP3908DK-LF-P is housed in a thermally enhanced 10-pin MSOP package (3.0 mm × 3.0 mm × 1.0 mm), rated for –40°C to +85°C ambient operation and featuring 150°C/W junction-to-ambient thermal resistance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar current-mode synchronous PWM controller applications.

Compared with UCC28064A and LM5022, the MP3908DK-LF-P uniquely integrates dual independent gate drivers, resistor-programmable dead-time, and lossless current sensing - making it the only solution among the three capable of fully self-contained synchronous flyback implementation without auxiliary timing ICs or discrete drivers.

Availability

MP3908DK-LF-P is available at Aetrix Electronics and suitable for PoE PD power supplies, telecom isolated power modules, TV CCFL backlight generation, and industrial off-line boost converters requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for MP3908DK-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 mixed-signal ICs for power management, with expertise in DC/DC conversion, LED drivers, and motor control.

The MP3908 belongs to MPS's high-efficiency current-mode PWM controller product line, engineered specifically for isolated and non-isolated DC/DC topologies demanding synchronous rectification, low quiescent current, and robust cycle-by-cycle protection.

FAQ

What is the maximum allowable voltage on the ISENSE pin?

The ISENSE pin has an absolute maximum rating of +28 V. When used in lossless sensing mode, it must connect directly to the drain of the main MOSFET only if the peak drain voltage remains ≤28 V. Exceeding this risks permanent damage; for higher-voltage applications, a sense resistor must be used instead.

How is dead-time controlled on the MP3908DK-LF-P?

Dead-time is set by an external resistor (RDELAY) tied from Pin 5 to ground. The internal 50 kΩ resistor combines with the external value to determine delay duration - e.g., 100 kΩ yields ~50 ns. This delay occurs between SYNC gate turn-off and MAIN gate turn-on to prevent shoot-through.

Can the MP3908DK-LF-P operate in discontinuous conduction mode (DCM)?

Yes - the MP3908DK-LF-P supports both continuous and discontinuous conduction modes. Its current-mode architecture and slope compensation ensure stable operation across DCM boundaries, particularly in flyback and SEPIC configurations with light loads or high turns ratios.

What is the purpose of the CSS pin, and how is it sized?

The CSS pin accepts an external capacitor charged by a 5 µA internal current to implement soft-start. To achieve a 10 ms ramp time, use C = t × I / ΔV = 10 ms × 5 µA / 2.7 V ≈ 18.5 nF. A 22 nF ceramic capacitor is commonly selected for margin and temperature stability.

Does the MP3908DK-LF-P support external synchronization of switching frequency?

No - the MP3908DK-LF-P operates at a fixed internal oscillator frequency of 250 kHz (±20%). It does not include an external sync input or frequency programming interface; frequency variation is limited to the specified 220–300 kHz range due to process and temperature drift.

What thermal considerations apply to the MSOP10 package?

The MSOP10 package has θ_JA = 150°C/W on a 1"² 1 oz copper PCB. For reliable operation at full load, keep junction temperature below 125°C. Use thermal vias under the exposed pad (if present per variant) and minimize trace length to GND to reduce thermal resistance.

Is the FB pin internally clamped, and why does it matter?

Yes - the FB pin is internally clamped to ≤1.2 V to prevent error amplifier saturation during startup or fault conditions. This ensures fast recovery from overvoltage events and maintains COMP node linearity, preserving loop stability during transient load steps.