Monolithic Power Systems Inc. NB671LAGQ-Z

Overview

NB671LAGQ-Z from Monolithic Power Systems is a high-current, low-quiescent-current synchronous step-down DC/DC converter designed for compact, high-efficiency power delivery in space-constrained systems. It delivers 6A continuous and 9A peak output current across a 5.5V–24V input range, features Constant-On-Time (COT) control for fast transient response, and integrates dual MOSFETs with 30mΩ/15mΩ R_DS(ON). It supports adjustable output from 0.604V to 5.5V and is used in laptop and tablet main power rails.

For engineers reviewing the NB671LAGQ-Z datasheet, NB671LAGQ-Z pinout, NB671LAGQ-Z application, or NB671LAGQ-Z equivalent, key selection criteria include its 120μA quiescent current in LP#-enabled light-load mode, 500kHz switching frequency (adjustable down to ~150kHz at low VIN/VOUT ratios), open-drain PGOOD signaling, and integrated OCP/OVP/UVP/thermal shutdown with latch-off reset via EN or power cycle.

Technical Context

The NB671LAGQ-Z employs proprietary Constant-On-Time (COT) control with internal ramp compensation, enabling stable operation with ceramic output capacitors without external compensation. Its valley-current overcurrent protection uses the low-side MOSFET's R_DS(ON) as the current-sense element, triggering cycle-by-cycle limiting at 7.8–9.5A.

It integrates a 5V internal LDO (VCC) for gate drivers and control logic, supports dynamic low-power mode via active-low LP# (reducing I_Q to 60μA), and implements output discharge via an internal 6Ω MOSFET-distinct from low-side FET conduction-to prevent negative VOUT during shutdown.

Key Specifications

Pinout & Package

Package: QFN16 (3mm × 3mm, exposed thermal pad). Compact footprint supports high-density PCB layouts with efficient thermal dissipation via bottom-side copper.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-current synchronous step-down converter applications.

Compared with MP2451DT-LF-Z and RT7272BGJ8F, NB671LAGQ-Z uniquely combines 6A capability, LP#-enabled 60μA quiescent current, and internal output discharge-making it the only option among the three qualified for battery-sensitive, high-current, single-chip POL designs requiring autonomous fault-safe shutdown.

Availability

NB671LAGQ-Z is available at Aetrix Electronics and suitable for laptop computers, tablet PCs, and flat-panel display logic supplies requiring stable component supply amid end-of-life transitions.

Supply support for NB671LAGQ-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 a focus on energy-efficient DC/DC conversion and motor control solutions.

NB671LAGQ-Z belongs to MPS's high-current synchronous buck converter product line, engineered for compact, high-efficiency point-of-load power in portable and space-constrained computing systems.

FAQ

What is the function of the LP# pin, and how does it affect efficiency?

The LP# (Low Power) pin is an active-low input that reduces quiescent current from 120μA to 60μA in light-load conditions, significantly improving efficiency below 10mA output. When asserted, it modifies internal biasing to minimize control circuit consumption while maintaining regulation. It is 3.3V-tolerant and draws only 1μA, allowing direct connection to system GPIO or logic-level signals.

Does NB671LAGQ-Z require external compensation for ceramic output capacitors?

No-NB671LAGQ-Z includes internal ramp compensation specifically designed to stabilize Constant-On-Time control with low-ESR ceramic output capacitors. This eliminates the need for external RC networks in most designs, simplifying layout and reducing BOM count. External ramp is only required in edge cases involving very high output capacitance or extreme EMI constraints.

How does the output discharge feature operate, and what is its resistance?

The output discharge function activates automatically when EN is low or during fault shutdown (OVP/OCP/UVP/thermal). An internal 6Ω MOSFET connects VOUT to PGND, safely bleeding stored charge without relying on the low-side switch. This prevents residual voltage from interfering with downstream logic sequencing and meets strict system-level power-down requirements.

What is the minimum recommended input voltage for stable 5V output operation?

The NB671LAGQ-Z supports 5V output from as low as 5.5V input due to extended duty cycle capability (up to 95.5%) and adaptive COT timing. At VIN = 5.5V, switching frequency drops to ~150kHz to maintain regulation-verified in the datasheet's typical performance curves. Input capacitance must be sized for worst-case ripple at this low VIN margin.

Can the PGOOD signal drive a microcontroller GPIO directly?

Yes-the PG pin is an open-drain output rated for 4mA sink current at 0.4V. It can directly interface with 3.3V or 5V logic inputs using a pull-up resistor (e.g., 100kΩ to VCC). The 0.5ms delay from FB ≥ 95% VREF to PG high ensures robust sequencing, and the 85% VREF falling threshold provides clean fault indication without chatter.

Is NB671LAGQ-Z pin-compatible with the standard NB671 series?

Yes-NB671LAGQ-Z is pin-to-pin compatible with NB671, except that Pin 3 is redefined from NC to LP#. All other pins retain identical functions and placement. This allows drop-in replacement in existing NB671 designs when low-power mode is added, provided the LP# signal is properly routed and terminated.

What thermal derating applies above +85°C ambient temperature?

With θ_JA = 70°C/W on a 4-layer PCB, the device dissipates up to 1.8W at +25°C ambient. Above +85°C, derating follows PD_MAX = (150°C − T_A) / 70°C/W. At +105°C ambient, maximum continuous power drops to ~0.64W-requiring reduced load current or enhanced heatsinking via the exposed thermal pad and PCB copper area.