Monolithic Power Systems Inc. MP3908DK-LF-Z

Overview

MP3908DK-LF-Z 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, 0.818 V feedback reference, 270 µA typical operating current, and dual 10 V gate drivers capable of >10 A MOSFETs-enabling PoE PD and telecom isolated power supplies.

For engineers reviewing the MP3908DK-LF-Z datasheet, MP3908DK-LF-Z pinout, MP3908DK-LF-Z application, or MP3908DK-LF-Z equivalent, key selection criteria include programmable dead-time control, lossless current sense (≤28 V), cycle-by-cycle current limiting, slope compensation, and RDELAY-adjustable synchronous-to-main gate delay for optimal efficiency in isolated DC-DC designs.

Technical Context

The MP3908DK-LF-Z implements a peak-current-mode control architecture with an internal 0.818 V reference error amplifier, transconductance gain of 0.32 mA/V, and translator gain of 0.32 V/V. Its COMP node interfaces with external RC compensation to stabilize loops across boost and isolated flyback configurations.

It integrates dual gate drivers: MAIN GATE (Pin 9) and SYNC GATE (Pin 10), each with 16 Ω sourcing / 5.0 Ω sinking impedance, 10 V compliance, and externally programmable turn-off delay via RDELAY (Pin 5). The ISENSE (Pin 6) supports direct drain-sense below 28 V, eliminating external shunts in low-voltage boost applications.

Key Specifications

Pinout & Package

The MP3908DK-LF-Z is housed in a space-saving 10-pin MSOP package (3.0 mm × 3.0 mm × 1.0 mm), rated for –40°C to +85°C ambient operation, with exposed thermal pad for enhanced power dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with UCC28064DR and LM5122MH/NOPB, the MP3908DK-LF-Z uniquely combines 250 kHz fixed-frequency control, dual independent gate drivers, and lossless current sensing-making it the only choice for cost-sensitive, efficiency-critical 28 V-class synchronous boost and isolated flyback designs requiring <100 µA shutdown current and MSOP footprint.

Availability

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

Supply support for MP3908DK-LF-Z 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 synchronous rectified boost, flyback, and SEPIC topologies in telecom, industrial, and consumer power applications demanding low quiescent current and minimal external components.

FAQ

What is the maximum allowable voltage on the ISENSE pin?

The ISENSE pin has an absolute maximum rating of +28 V. Exceeding this voltage risks permanent damage. For applications with higher drain swings-such as 48 V output boost-the pin must be connected through a resistive divider or isolated current sense amplifier to maintain signal integrity and safety.

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

Yes, the MP3908DK-LF-Z supports both continuous and discontinuous conduction modes. Its current-mode architecture and slope compensation remain effective in DCM, though slope compensation may be reduced or disabled per design notes to avoid over-compensation at light loads.

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

RDELAY sets delay via internal 50 kΩ bias plus external resistance. A 100 kΩ external resistor yields ~50 ns delay; 0 Ω yields ~30 ns. Use the datasheet's Figure 7 (Delay vs. RDELAY) for precise interpolation-no formula is provided, and values beyond 200 kΩ yield diminishing returns.

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

No, the MP3908DK-LF-Z operates at a fixed internal oscillator frequency of 250 kHz and does not provide an external sync input. Frequency adjustment is limited to ±20 kHz tolerance; for synchronized multi-phase systems, external clock injection is not supported.

What is the recommended minimum trace width for the MAIN GATE and SYNC GATE outputs?

For reliable 10 A peak gate drive, use ≥12 mil (0.3 mm) trace width with 2 oz copper and adjacent ground pour. Keep traces under 5 mm length and avoid vias to minimize inductance-excessive inductance causes ringing, delayed turn-on, and increased switching loss in high-speed MOSFETs.

Is the FB pin internally clamped, and what happens if it exceeds 1.2 V?

Yes, the FB pin is internally clamped at 1.2 V. Sustained voltage above this level can cause comparator saturation, leading to loss of regulation, erratic duty cycle, or temporary latch-up. External Zener or resistor divider limiting is strongly advised in noisy environments or during startup overshoot.

What thermal derating applies above 85°C ambient?

The MP3908DK-LF-Z is rated for operation up to +85°C ambient. Above this, power dissipation must be reduced per θ_JA = 150 °C/W: for every 10°C rise, maximum allowable power drops by ~67 mW. Derating curves are not published; thermal shutdown at 150°C provides last-resort protection.