Monolithic Power Systems Inc. MP1518DJ-LF-Z

Overview

MP1518DJ-LF-Z from Monolithic Power Systems is a fixed-frequency, current-mode boost LED driver IC designed to drive up to 6 series white LEDs from a 2.5V–6V input (e.g., single-cell Li-ion). It integrates a 0.5Ω power MOSFET switch, regulates LED current via a 104mV feedback reference, and features open-load shutdown at 28V on the OV pin. Used in compact portable displays requiring high efficiency (up to 87%) and EMI-conscious layout.

For engineers reviewing the MP1518DJ-LF-Z datasheet, MP1518DJ-LF-Z pinout, MP1518DJ-LF-Z application, or MP1518DJ-LF-Z equivalent, key selection criteria include its 1.0–1.5MHz fixed switching frequency, TSOT23-6 package footprint, 104mV FB threshold for low-loss current sensing, thermal/UVLO protection, and PWM/DC dimming support - all critical for battery-powered LED backlighting.

Technical Context

The MP1518DJ-LF-Z implements a constant-frequency peak-current-mode boost architecture with internal slope compensation to prevent subharmonic oscillation above 50% duty cycle. Its error amplifier compares FB voltage against a precision 104mV reference, modulating the 0.5Ω integrated MOSFET's on-time to maintain regulated LED current.

Protection functions are hardware-based and autonomous: OV pin monitors output voltage and latches off the converter at ≥28V; under-voltage lockout engages below 2.25V (with 92mV hysteresis); thermal shutdown activates at 160°C; and internal current limiting caps switch conduction at 350mA under 60% duty cycle.

Key Specifications

Pinout & Package

MP1518DJ-LF-Z is packaged in a 6-pin TSOT23 (0.95 mm × 1.45 mm × 0.90 mm), optimized for space-constrained portable designs. Pin 1 is bottom-left when reading top marking left-to-right.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar white LED boost driver applications.

Compared with MP1518DJE, the MP1518DJ-LF-Z offers higher EMI margin for cost-sensitive designs; versus RT9397B, it delivers lower system-level BOM cost and intrinsic safety via integrated OV detection - critical for unattended portable devices.

Availability

MP1518DJ-LF-Z is available at Aetrix Electronics and suitable for cell phone backlighting, digital still camera displays, and handheld PDA applications requiring stable component supply, RoHS-compliant packaging, and long-term production continuity.

Supply support for MP1518DJ-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 power ICs, with design centers in the US, China, and Taiwan, and global manufacturing partnerships.

The MP1518 belongs to MPS's White LED Driver product line, engineered specifically for space- and efficiency-constrained portable backlighting applications requiring integrated protection, low quiescent current, and robust thermal performance.

FAQ

What is the maximum number of white LEDs the MP1518DJ-LF-Z can drive?

The MP1518DJ-LF-Z is rated to drive up to 6 series white LEDs, assuming typical forward voltage of 3.0–3.4V per LED and input voltage ≥3.6V. At VIN = 3.6V, the 92% max duty cycle supports ~18V output, sufficient for six 3.0V LEDs (18V total VF). Efficiency drops above 5 LEDs under low-input conditions.

Does the MP1518DJ-LF-Z require an external Schottky diode?

Yes - the MP1518DJ-LF-Z requires an external Schottky diode connected between SW and the LED string anode. The IC integrates only the high-side MOSFET switch; the diode provides the freewheeling path during MOSFET off-time. A 100–200mA-rated Schottky with low V_F (e.g., CMDSH-3) is recommended per the datasheet.

How is LED current set, and what resistor value is needed for 20mA?

LED current is set by the external sense resistor (R_SENSE) between FB and GND, using I_LED = 104mV / R_SENSE. For 20mA, R_SENSE = 104mV / 0.02A = 5.2Ω. The datasheet confirms this value in Table 2 and recommends 1% tolerance metal-film or thick-film resistors for accuracy.

Can the MP1518DJ-LF-Z operate from a 2.5V input?

Yes - the MP1518DJ-LF-Z operates across 2.5V to 6V input. At 2.5V, it can drive up to 3–4 white LEDs (depending on VF) due to duty cycle limitation (max 92%). Startup is guaranteed above the 2.25V UVLO threshold, and quiescent current remains ≤750µA, preserving battery life in standby.

What happens during an open LED condition?

When an LED opens, the OV pin - tied to the LED string anode - detects rising output voltage. At ≥28V, the MP1518DJ-LF-Z immediately disables switching and latches off. Recovery requires cycling IN supply voltage; no automatic retry occurs, preventing repeated stress on remaining LEDs or components.

Is thermal derating required for the TSOT23-6 package?

Yes - the TSOT23-6 has θ_JA = 220°C/W. At 25°C ambient and 350mA switch current, power dissipation can reach ~60mW (I²R + switching losses), raising junction temperature by ~13°C. In enclosed or high-ambient environments (>60°C), output current must be reduced per the thermal derating curve in the datasheet to stay below 125°C T_J.

Does the MP1518DJ-LF-Z support analog dimming without external transistors?

Yes - analog dimming is supported directly at the FB pin using a DC voltage source (e.g., DAC or potentiometer) in series with resistors R2/R3 as shown in Figure 6. Injecting current into FB reduces effective sense voltage, proportionally lowering LED current. No external transistor or op-amp is required for basic linear dimming.