Monolithic Power Systems Inc. MP3908DK-LF

Overview

MP3908DK-LF 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 250kHz constant-frequency operation, 10V gate drivers capable of >10A MOSFETs, programmable dead-time control, and lossless current sensing (≤28V drain voltage). Used in PoE PD power supplies and telecom isolated power modules.

For engineers reviewing the MP3908DK-LF datasheet, MP3908DK-LF pinout, MP3908DK-LF application, or MP3908DK-LF equivalent, key selection criteria include its 0.818V feedback reference, 270µA typical operating current, 50ns minimum on-time, cycle-by-cycle current limiting, and resistor-programmable synchronous delay via RDELAY pin - all critical for stable high-efficiency DC-DC design.

Technical Context

The MP3908DK-LF implements a constant-frequency peak current-mode control architecture with an internal 0.8V reference error amplifier, transconductance gain of 0.32mA/V, and slope compensation to ensure loop stability across duty cycles. Its dual gate drivers (MAIN and SYNC) operate with matched sourcing/sinking impedances (16Ω/5Ω), enabling precise timing control between primary and secondary switches.

Functional block integration includes under-voltage lockout (4.7V turn-on threshold), soft-start via CSS pin (5µA charging current), and an IMAX clamp that limits ISENSE voltage to 190mV for cycle-by-cycle protection. The RDELAY pin accepts external resistors (with 50kΩ internal pull-up) to program 30ns–500ns delay between synchronous rectifier turn-off and main switch turn-on - essential for preventing shoot-through in isolated topologies.

Key Specifications

Pinout & Package

The MP3908DK-LF is housed in a thermally enhanced 10-pin MSOP package (3.0mm × 4.9mm, 0.5mm pitch), rated for –40°C to +85°C operation and compatible with standard reflow profiles.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC28064DR and NCP1252ADR2G, the MP3908DK-LF uniquely integrates synchronous secondary drive, resistor-programmable dead-time, and lossless current sensing - making it the only option among the three qualified for high-efficiency isolated boost/flyback designs requiring <50µA shutdown current and 250kHz operation.

Availability

MP3908DK-LF is available at Aetrix Electronics and suitable for PoE PD power supplies, telecom isolated power systems, TV CCFL generation, and brick module auxiliary supplies requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for MP3908DK-LF 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 core expertise in DC-DC conversion, LED drivers, and motor control solutions.

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 precision timing, low quiescent power, and integrated synchronous rectification control.

FAQ

What is the maximum allowable voltage on the ISENSE pin?

The ISENSE pin has an absolute maximum rating of +28V. Exceeding this voltage risks permanent damage. For lossless sensing, connect directly to the MOSFET drain only when the drain voltage swing remains ≤28V; otherwise, use a dedicated current-sense resistor to avoid exceeding the rating.

Can the MP3908DK-LF be used in discontinuous conduction mode (DCM)?

Yes - the MP3908DK-LF operates reliably in DCM, CCM, and boundary conduction modes. Its peak current-mode architecture inherently adapts to load and input variations, and slope compensation ensures stability across all modes without external adjustment.

How is the RDELAY resistor value calculated for a desired dead-time?

RDELAY value is determined by subtracting the internal 50kΩ pull-up from the total resistance needed for target delay. For example, a 100kΩ external resistor yields ~150kΩ total, producing ~50ns delay per Figure 1 in the datasheet. Use the provided delay vs. RDELAY graph (Rev.0.9, p.5) for precise selection.

Does the MP3908DK-LF support external synchronization?

No - the MP3908DK-LF operates with an internal oscillator only and does not provide an external sync input or clock output. Its 250kHz switching frequency is factory-trimmed and not user-adjustable beyond tolerance (±10%).

What is the recommended minimum output capacitance for stable regulation?

For stable loop response, the output capacitor must provide sufficient ESR zero and phase margin. With typical 250kHz operation and 5A load, ≥10µF ceramic (or equivalent low-ESR tantalum) is required; datasheet Example 1 specifies 14.5µF minimum for 1% ripple at 25V output.

Is the FB pin internally clamped?

Yes - the FB pin is internally clamped to 1.2V maximum. Exceeding this voltage risks saturating the error amplifier and disrupting regulation. External voltage dividers must be designed so FB never rises above 1.2V, even during transient overvoltage conditions.

What thermal derating applies above 85°C ambient?

The device is rated for operation up to +85°C ambient. Beyond this, junction temperature must remain ≤125°C. With θJA = 150°C/W, power dissipation must be reduced by 1.25mW/°C above 85°C - e.g., at 100°C ambient, max dissipation drops to ~18.75mW unless board-level heatsinking improves θJA.