Monolithic Power Systems Inc. NB679GD-Z

Overview

NB679GD-Z from Monolithic Power Systems is a fully integrated, synchronous buck converter with fixed 5 V/8 A output and integrated 5 V/100 mA LDO. It operates from 5.5 V to 24 V input, uses adaptive constant-on-time (COT) control, delivers 700 kHz switching frequency, and integrates low-R_DS(on) MOSFETs (HS: 25 mΩ, LS: 12 mΩ) for high efficiency across load range. It targets compact, high-current point-of-load regulation in portable computing and display systems.

For engineers reviewing the NB679GD-Z datasheet, NB679GD-Z pinout, NB679GD-Z application, or NB679GD-Z equivalent, this device is selected for fixed-output, high-current DC/DC conversion where ultrasonic mode operation, internal soft-start, power-good signaling, and LDO switch-over capability are required in space-constrained designs.

Technical Context

The NB679GD-Z implements adaptive COT control with DC auto-tune loop feedback to maintain tight line/load regulation while enabling fast transient response without external compensation. Its valley-current overcurrent protection uses the low-side MOSFET's R_DS(on) as a sensing element, eliminating need for external sense resistors.

It supports dual operating modes: normal PWM mode above critical load (~3.5 A at 12 V_IN) and ultrasonic mode (≥25 kHz) during light/no-load via EN voltage thresholding (1.4–1.8 V). The integrated 5 V LDO switches over to VOUT when output exceeds 4.8 V, reducing dropout loss and improving standby efficiency.

Key Specifications

Pinout & Package

Package: QFN-12 (2 mm × 3 mm, 0.5 mm pitch, exposed thermal pad). Pin 1 marked with dot; pins arranged counterclockwise. Exposed pad must be soldered to PCB ground plane for thermal and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPQ4572GQB-AEC1-Z and RT7295BGJ6F, the NB679GD-Z uniquely combines integrated LDO with automatic VOUT switch-over, ultrasonic mode, and adaptive COT control in a 2 mm × 3 mm package-enabling simpler, quieter, and more thermally efficient 5 V/8 A designs without external compensation or sense resistors.

Availability

NB679GD-Z is available at Aetrix Electronics and suitable for laptop mainboards, tablet SoC power domains, flat-panel display logic boards, and distributed networking nodes requiring stable component supply, long-lifecycle support, and RoHS-compliant packaging.

Supply support for NB679GD-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 NB679GD-Z belongs to MPS's NB-series high-current DC/DC converters, designed specifically for compact, high-efficiency point-of-load regulation in portable computing and visual display systems where thermal density and acoustic noise are critical constraints.

FAQ

What is the minimum input voltage required for the NB679GD-Z to start switching?

The NB679GD-Z has an input under-voltage lockout (UVLO) with a rising threshold of 4.7 V (typical). It begins switching only when VIN rises above this value. The hysteresis is 450 mV, so the falling threshold is approximately 4.25 V. Below 4.25 V, the device remains disabled and draws ≤2 µA.

Can the NB679GD-Z operate with only ceramic output capacitors?

Yes-the NB679GD-Z is internally compensated for stable operation with ceramic output capacitors. Its adaptive COT architecture and DC auto-tune loop eliminate the need for ESR-based damping, allowing use of low-ESR X5R/X7R ceramics (e.g., 4.7 µF to 88 µF) without oscillation or excessive ripple.

How does the LDO switch-over function work, and when does it activate?

The internal 5 V LDO automatically switches its input source from internal VCC to VOUT when the buck output reaches 4.8 V and the PG signal asserts. This occurs after soft-start completes and VFB stabilizes. Switch-over reduces LDO dropout loss, improving efficiency by ~12% at 100 mA load.

What happens during an overcurrent event, and how is recovery handled?

During overcurrent, the NB679GD-Z triggers valley-current limiting using the low-side MOSFET's R_DS(on). If the sensed current exceeds 11 A (typ), the controller halts new switching cycles. Fault latching persists until EN is pulled low or VIN is power-cycled-no automatic retry.

Is the NB679GD-Z compatible with pre-biased output conditions?

Yes-the NB679GD-Z supports pre-biased start-up. When EN goes high and VOUT is already above the target, the IC disables both high-side and low-side switches until the internal reference voltage ramps above the sensed FB voltage, preventing reverse current flow and output overshoot.

What thermal derating applies to the 8 A rating in the QFN-12 package?

The 8 A continuous rating assumes θ_JA = 70°C/W on a 4-layer PCB with full thermal pad soldering. At ambient temperature of 85°C, maximum continuous current drops to ~5.5 A due to thermal limits (T_J ≤ 125°C). Derating curves are provided in Figure 7 of the datasheet Rev. 1.03.

Does the NB679GD-Z require a bootstrap capacitor, and what value is recommended?

Yes-a 0.1 µF X7R ceramic capacitor is required between BST and SW pins. It must be placed within 2 mm of the IC with short, wide traces. This capacitor supplies gate drive for the high-side MOSFET and must withstand voltage stress up to V_IN + 4.5 V.