Monolithic Power Systems Inc. NB649EQJ-LF-P

Overview

NB649EQJ-LF-P from Monolithic Power Systems is a synchronous step-down DC/DC converter with integrated 100mA LDO, delivering 8A continuous output current across 5.5V–25V input range, fixed 600kHz switching frequency, and adjustable output voltage from 0.8V to 15V. It integrates high- and low-side MOSFETs (R_DS(ON) = 50mΩ / 8mΩ), power good output, thermal shutdown, and OCP-designed for notebook I/O power rails requiring compact, high-current regulation.

For engineers reviewing the NB649EQJ-LF-P datasheet, NB649EQJ-LF-P pinout, NB649EQJ-LF-P application, or NB649EQJ-LF-P equivalent, key selection criteria include its dual-regulator architecture (buck + LDO), 30-pin QFN package thermal performance (θ_JA = 42°C/W), SELH-selectable LDO output (3.3V/5V), and sync capability from 300kHz to 1MHz.

Technical Context

The NB649EQJ-LF-P implements peak-current-mode control with internal compensation, enabling stable regulation without external loop components. Its error amplifier compares FB voltage against a precise 0.808V reference and drives COMP to modulate high-side switch conduction time.

It features dual power domains: a main buck regulator with bootstrap-driven high-side gate driver (BST pin), and an independent LDO (enabled via ENLDO) with selectable 3.3V/5V output (SELH-controlled) and 5Ω R_DS(ON). Thermal shutdown triggers at 150°C with 10°C hysteresis, and hiccup-mode OCP activates when FB drops below 70% of regulation.

Key Specifications

Pinout & Package

Package: 5mm × 6mm, 30-pin QFN with exposed thermal pad (JEDEC MO-220 VHJD). Pin 1 marked by corner notch or dot; pins 9–15 and 27–29 are GND; pin 21 is VCC bias supply; pin 20 is analog ground (AGND) for noise-sensitive circuitry.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous buck + LDO applications.

Compared with NB649EQJ-LF-P, NB700 offers higher efficiency and broader input range but requires layout changes, while NB693A preserves mechanical compatibility at the cost of halved LDO output capability-making NB693A suitable only for minimal LDO load scenarios.

Availability

NB649EQJ-LF-P is available at Aetrix Electronics and suitable for notebook I/O power, networking ASIC supplies, distributed POL systems, and industrial embedded controllers requiring stable component supply despite end-of-life status.

Supply support for NB649EQJ-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 core expertise in DC/DC conversion, motor drivers, and LED lighting controllers.

The NB649 belongs to MPS's high-current synchronous buck converter product line, designed specifically for space-constrained computing and communications applications demanding integrated power management with minimal external components.

FAQ

What does "END OF LIFE, REFER TO NB700 OR NB693A" mean for NB649EQJ-LF-P?

This designation indicates Monolithic Power Systems has discontinued active manufacturing of NB649EQJ-LF-P. While Aetrix Electronics maintains legacy stock and supports existing designs, new projects should migrate to NB700 (enhanced successor) or NB693A (pin-compatible alternative) per MPS's official migration guidance.

Can NB649EQJ-LF-P operate with input voltage below 5.5V?

No. The absolute minimum operating input voltage is 5.5V per the Recommended Operating Conditions table. Although Absolute Maximum Ratings list VIN down to 4.5V, the device is not guaranteed to regulate or maintain specifications below 5.5V, and startup may fail due to VCC UVLO (4.0V threshold).

How is the LDO output voltage selected between 3.3V and 5V?

The SELH pin determines LDO output: grounding SELH sets VLDO to 5V (±250mV), while pulling SELH to ≥2V (e.g., via resistor divider from VIN or VOUT) selects 3.33V (±170mV). This selection is active only when ENLDO is high and REGO is connected appropriately.

What is the purpose of the REGO pin, and how should it be connected?

REGO connects the internal LDO's input to the main buck output (VOUT) instead of VIN. When VOUT is present and ≥3.3V, this improves LDO efficiency by reducing dropout voltage and heat generation. If VOUT is unavailable at startup, connect REGO to VIN via a diode or leave unconnected for default VIN sourcing.

Does NB649EQJ-LF-P require an external bootstrap diode?

No - the device integrates a bootstrap diode. An external diode (e.g., IN4148) is optional and recommended only when duty cycle exceeds 65% (e.g., VOUT ≥5V with VIN=12V) to reduce BST capacitor charging losses and improve light-load efficiency.

What thermal derating applies above +25°C ambient?

With θ_JA = 42°C/W on a 4-layer PCB, maximum continuous power dissipation decreases linearly: PD_MAX = (125°C − T_A) / 42°C/W. At +60°C ambient, max dissipation drops to ~1.55W - requiring careful layout, copper area, and airflow to sustain 8A output without thermal shutdown.

Is the PG (Power Good) signal compatible with 3.3V logic systems?

Yes. PG is an open-drain output with 4mA sink capability and 0.4V max saturation voltage at 4mA. It can be pulled up to 3.3V (or 5V) with a 10kΩ resistor, producing a clean logic-high signal for microcontroller reset or enable inputs without level-shifting.