Monolithic Power Systems Inc. NB679AGD-Z

Overview

NB679AGD-Z from Monolithic Power Systems is a fully integrated synchronous buck converter with fixed 5.1V output, 8A continuous current capability, integrated 5V/100mA LDO, and LP#-controlled VOUT scaling (4.85V in low-power mode). It operates from 5.5V–24V input, uses adaptive constant-on-time control, and delivers stable power to core logic rails in space-constrained portable systems.

For engineers reviewing the NB679AGD-Z datasheet, NB679AGD-Z pinout, NB679AGD-Z application, or NB679AGD-Z equivalent, key selection criteria include its QFN-12 (2mm × 3mm) footprint, ultrasonic mode for audible-noise-sensitive designs, DC auto-tune loop for ±0.5% load regulation, and dual-mode EN pin enabling seamless transition between normal and ultrasonic operation.

Technical Context

The NB679AGD-Z implements adaptive constant-on-time (COT) control with DC auto-tune feedback to maintain tight output regulation across line and load variations while enabling fast transient response without external compensation. Its internal high-side (25mΩ) and low-side (12mΩ) MOSFETs support up to 10A peak current and enable >92% efficiency at 5A/12V_IN–5.1V_OUT.

It integrates three independent voltage regulation functions: primary 5.1V/8A buck output, auxiliary 5V/100mA LDO with switch-over to VOUT when PG asserts, and LP#-selectable low-power mode (4.85V) for system-level power state coordination. Protection includes valley-current OCP, 122% OVP, dual-threshold UVP (75% and 50% V_REF), thermal shutdown at 140°C, and output discharge via internal 6Ω FET.

Key Specifications

Pinout & Package

Package: QFN-12 (2mm × 3mm, 0.5mm pitch, exposed thermal pad).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP2451DT-LF-Z and RT7272BGJ6F, the NB679AGD-Z uniquely integrates 8A power delivery, 5V LDO, LP#-based VOUT scaling, and ultrasonic mode in a 2mm × 3mm QFN-enabling single-chip power architecture for next-gen portable and embedded systems.

Availability

NB679AGD-Z is available at Aetrix Electronics and suitable for laptop computers, tablet PCs, and flat-panel display logic supplies requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for NB679AGD-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 NB679AGD-Z belongs to MPS's NB-series high-current synchronous buck converters, engineered specifically for space-constrained, high-efficiency computing and consumer electronics power delivery where integration, thermal performance, and intelligent power-state management are critical.

FAQ

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

The LP# pin is an active-low logic input that controls output voltage scaling: when left open or pulled high, VOUT is regulated to 5.1V; when driven low, VOUT scales to 4.85V. This enables hardware-coordinated entry into low-power system states (e.g., S3/S5) without software intervention, reducing idle power by ~5% in typical notebook workloads.

Does the NB679AGD-Z require external compensation components?

No. The NB679AGD-Z uses adaptive constant-on-time (COT) control with an integrated DC auto-tune loop, eliminating the need for external compensation networks. It remains stable with POSCAP or ceramic output capacitors - verified across 10μF–100μF ranges and ESR values from 1mΩ to 20mΩ.

How does the ultrasonic mode (USM) operate, and what triggers it?

Ultrasonic mode activates automatically when the EN pin voltage is held between 1.4V and 1.8V. In USM, the controller extends off-time to maintain regulation while keeping switching frequency above 20kHz, suppressing audible noise from inductor vibration during light-load or standby conditions - critical for premium consumer audio-visual devices.

What is the purpose of the VOUT pin, and why must it be routed with special care?

The VOUT pin serves dual roles: it senses the output voltage for regulation feedback and provides the input to the internal LDO switch-over circuit. It must be routed as a Kelvin sense trace (>25 mil width, no vias, isolated from SW node) to avoid noise coupling and ensure accurate regulation and reliable LDO handover at 4.8V.

Can the NB679AGD-Z safely drive pre-biased outputs during start-up?

Yes. The NB679AGD-Z includes pre-bias start-up protection: if the output is already biased above the soft-start ramp target when EN goes high, the controller disables both high-side and low-side switches until the internal reference voltage exceeds the sensed FB voltage, preventing reverse current flow and output collapse.

What thermal management considerations apply to the QFN-12 package?

The QFN-12 (2mm × 3mm) package has θ_JA = 70°C/W on a 4-layer JEDEC board. For 8A operation at 12V_IN, thermal pad soldering to ≥2 internal copper layers and ≥6 thermal vias is mandatory. Junction temperature must stay below 125°C continuous; thermal shutdown activates at 140°C with 25°C hysteresis.

How does the integrated LDO interact with the main buck output?

The 5V/100mA LDO powers internal control logic and can supply external peripherals. Once VOUT reaches 4.8V and PG asserts, an internal MOSFET switches the LDO input from VCC to VOUT - reducing dropout loss and improving overall system efficiency by ~150mW at full LDO load.