Monolithic Power Systems Inc. NB671AGQ-P

Overview

NB671AGQ-P from Monolithic Power Systems is a fully integrated 5V–22V input, synchronous step-down DC/DC converter delivering 6A continuous and 9A peak output current with adjustable 0.604V–5.5V output voltage. It employs Constant-On-Time (COT) control, features internal 30mΩ/15mΩ MOSFETs, 500kHz switching frequency, and integrated power-good (open-drain PG), soft-start, and output discharge for point-of-load regulation in compact space-constrained systems.

For engineers reviewing the NB671AGQ-P datasheet, NB671AGQ-P pinout, NB671AGQ-P application, or NB671AGQ-P equivalent, key selection criteria include its COT-based transient response, internal MOSFET R_DS(ON), thermal shutdown at 150°C, 7ms soft-start, and compatibility with ceramic output capacitors without external ramp compensation.

Technical Context

The NB671AGQ-P uses Constant-On-Time (COT) control with internal ramp compensation to ensure stability with low-ESR ceramic output capacitors-eliminating need for external ramp networks. Its valley-current overcurrent protection monitors the low-side MOSFET's R_DS(ON) during the off-state to trigger cycle-by-cycle limiting at 8.5A typical.

Power sequencing is managed via EN pin with 1.25V threshold and 100mV hysteresis, while the open-drain PG signal asserts after FB reaches 95% V_REF with 0.5ms delay and de-asserts at 85% V_REF. Internal 5V LDO (VCC) powers control circuitry and requires ≥1µF X7R/X5R decoupling.

Key Specifications

Pinout & Package

Package: QFN16 (3mm × 3mm, exposed thermal pad). Pin count: 16 terminals, including 3 NC pins and dual SW connections for current sharing.

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 RT7295BGJ8F, the NB671AGQ-P uniquely combines 6A capability, COT control with internal ramp, adjustable output, PG, and output discharge in a 3×3mm QFN-making it optimal for space-constrained, high-transient-response POL applications despite its "Not Recommended for New Designs" status.

Availability

NB671AGQ-P is available at Aetrix Electronics and suitable for laptop computer power delivery, networking ASIC biasing, flat panel display logic rails, and distributed power system modules requiring stable component supply and long-lifecycle support.

Supply support for NB671AGQ-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 design centers in the US, China, and Taiwan, and global manufacturing partnerships.

The NB671AGQ-P belongs to MPS's high-current synchronous buck converter product line, engineered for compact, high-efficiency point-of-load regulation in computing, consumer, and industrial applications where thermal performance and transient response are critical.

FAQ

What does "NOT RECOMMENDED FOR NEW DESIGNS" mean for NB671AGQ-P?

This designation indicates MPS has superseded the NB671AGQ-P with newer-generation converters (e.g., MPQ4572 series) offering improved efficiency, lower quiescent current, or enhanced protection. However, NB671AGQ-P remains fully qualified, in active production, and supported with full documentation and lifetime buy options for legacy program continuity.

Can NB671AGQ-P operate with only ceramic output capacitors?

Yes. Its integrated ramp compensation eliminates reliance on output capacitor ESR for loop stability. Verified designs use three 22µF X5R/X7R ceramics (total 66µF) with no external ramp components, achieving stable PWM operation and <15mV p-p output ripple at full load.

How is the output voltage set, and what resistor tolerance is recommended?

VOUT is set by an external resistor divider from VOUT to AGND, connected to FB. With VREF = 604mV, R2 is typically 10kΩ; R1 = R2 × ((VOUT/0.604) − 1). Use 0.5% tolerance, 25ppm/°C metal-film or thin-film resistors to maintain ≤1% output accuracy across temperature and line regulation.

What is the purpose of the exposed thermal pad, and how should it be connected?

The exposed pad (Pins 8 & 9) is electrically connected to PGND and serves as the primary thermal path. It must be soldered to a minimum 100mm² copper pour with ≥6 thermal vias (0.3mm diameter) to an internal ground plane to achieve the specified θ_JA = 70°C/W and sustain 6A continuous current at +85°C ambient.

Does NB671AGQ-P support pre-biased output startup?

Yes. When VOUT is pre-charged before EN assertion, the IC disables both HS and LS switches until the internal reference voltage ramps above the sensed FB voltage. This prevents reverse current flow and ensures monotonic startup without output voltage overshoot or ringing.

How does the valley-current OCP respond during short-circuit conditions?

Under short-circuit, valley-current OCP triggers every cycle once inductor current exceeds 8.5A (typical), forcing immediate PWM inhibition. The controller then enters hiccup mode-repeated soft-start attempts every ~20ms-until fault clears, limiting average power dissipation and preventing thermal runaway.

Is the PG signal compatible with 3.3V logic systems?

Yes. PG is an open-drain output rated for 5.5V max. When pulled up to 3.3V via a 100kΩ resistor, it delivers valid logic-high (>2.4V) and logic-low (<0.4V) levels compatible with standard CMOS inputs, with sink current capability up to 4mA at 0.4V.