Monolithic Power Systems Inc. NB650GL-Z

Overview

NB650GL-Z from Monolithic Power Systems is a fully-integrated, synchronous step-down DC/DC converter delivering 6A continuous output current with 4.5V–28V input range, 0.6V–13V programmable output voltage, and constant-on-time (COT) control for fast transient response in notebook I/O and distributed power systems.

For engineers reviewing the NB650GL-Z datasheet, NB650GL-Z pinout, NB650GL-Z application, or NB650GL-Z equivalent, key selection criteria include its 2-bit VID dynamic voltage scaling, integrated 50mΩ/18mΩ MOSFETs, QFN17 (3mm×4mm) package, thermal shutdown at 150°C, and OCP behavior differences between NB650 (latch-off) and NB650H (hiccup mode).

Technical Context

The NB650GL-Z implements constant-on-time (COT) control with feed-forward input voltage modulation, enabling stable regulation across wide VIN/VOUT combinations without external compensation. Its internal high-side and low-side MOSFETs feature RDS(on) of 50mΩ and 18mΩ respectively, and the bootstrap circuit (BST pin) enables gate drive for the high-side switch.

Dynamic output voltage adjustment is achieved via two VID inputs controlling parallel FB-divider resistors (RFB1/RFB2), yielding four discrete VOUT levels. Protection logic includes cycle-by-cycle over-current detection with 50μs hold-off timer, non-latching UVLO (4V rising threshold), and open-drain Power Good (PG) with 0.9×VFB rising threshold and 0.5ms delay.

Key Specifications

Pinout & Package

Package: QFN17 (3mm × 4mm, 0.5mm pitch), exposed thermal pad on underside for enhanced heat dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP2451DT-LF-Z and RT7297CGQW, NB650GL-Z uniquely supports real-time 2-bit VID voltage scaling, wider 28V input capability, and COT-based sub-10μs transient response-making it suitable for high-performance portable and networking applications requiring adaptive power delivery.

Availability

NB650GL-Z is available at Aetrix Electronics and suitable for notebook I/O power, networking system rails, and flat-panel display logic supplies requiring stable component supply and long-term design continuity.

Supply support for NB650GL-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.

The NB650 series belongs to MPS's high-current synchronous buck converter product line, engineered for fast-transient, high-efficiency DC/DC conversion in space-constrained portable and infrastructure equipment.

FAQ

What is the purpose of the BST pin on NB650GL-Z?

The BST (bootstrap) pin connects to an external capacitor between SW and BST to generate a floating voltage supply for the high-side MOSFET gate driver. This enables full enhancement of the internal 50mΩ high-side switch without requiring a charge pump or external high-voltage bias source. Proper BST capacitor selection (typically 0.1μF X7R ceramic) and placement are critical for reliable operation above 12V input.

How does the 2-bit VID interface change output voltage without resetting the IC?

The VID1/VID2 pins control internal NMOS switches (RFB1/RFB2) that parallel external FB-divider resistors (R2A/R2B/R2C). As VID states change, the effective R2 value shifts, altering the FB divider ratio while maintaining continuous regulation. The COT control loop tracks the new reference instantly-no soft-start restart or digital register write is needed, enabling true on-the-fly voltage scaling.

Why does NB650GL-Z specify "NOT RECOMMENDED FOR NEW DESIGNS"?

This designation indicates MPS has released the NB650A as a pin-compatible, enhanced successor with improved efficiency, tighter reference tolerance, and updated protection thresholds. While NB650GL-Z remains fully functional and supported, new designs should evaluate NB650A for better long-term supply assurance, extended temperature performance, and reduced design risk.

Can NB650GL-Z operate with ceramic output capacitors?

Yes, but requires external ramp compensation via R4/C4 on the FB pin to ensure stability in PWM mode. Ceramic capacitors have low ESR, which reduces natural ramp slope on the FB node; without added ramp, subharmonic oscillation may occur. The datasheet provides equations to size R4 and C4 based on VIN, VOUT, and inductor value to maintain adequate noise immunity and phase margin.

What is the difference between NB650 and NB650H OCP behavior?

Under over-current or short-circuit conditions, NB650 enters latch-off mode and remains disabled until input power is cycled. NB650H uses hiccup mode: it disables the power stage, discharges the SS capacitor, waits, then attempts automatic restart. If the fault persists, it repeats the cycle-providing safer fault containment in systems where unattended recovery is required.

How is Power Good (PG) timing determined?

PG asserts high after FB reaches 90% of the 600mV reference voltage, with a fixed 0.5ms delay. The delay is independent of soft-start time and begins once the FB comparator threshold is crossed. PG deasserts when FB falls below 85% of reference, providing clean sequencing for downstream logic enablement and system reset coordination.