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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Voltage Regulators - DC DC Switching Regulators

Monolithic Power Systems Inc. NB639DL-LF-P

Name: NB639DL-LF-P
Brand: Monolithic Power Systems Inc.
SKU: NB639DL-LF-P
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: NB639DL-LF-P

Manufacturer:: Monolithic Power Systems Inc.

Category:: Voltage Regulators - DC DC Switching Regulators

Package:: 20-VFQFN Exposed Pad

Datasheet:: NB639DL-LF-P.pdf

Description:: IC REG BUCK ADJ 8A 20QFN

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Product details

Overview

NB639DL-LF-P from Monolithic Power Systems is a high-efficiency, fast-transient synchronous step-down DC/DC converter delivering 8A continuous output current from a 4.5V–28V input, featuring integrated 30mΩ/12mΩ MOSFETs, Constant-On-Time (COT) control, and 0.8V–13V adjustable output voltage in a QFN20 (3×4mm) package-designed for notebook I/O power and distributed POL systems.

For engineers reviewing the NB639DL-LF-P datasheet, NB639DL-LF-P pinout, NB639DL-LF-P application, or NB639DL-LF-P equivalent, key selection considerations include its COT-based transient response, external VCC biasing requirement, programmable soft-start, PGOOD open-drain signaling, and thermal shutdown with 25°C hysteresis.

Technical Context

The NB639DL-LF-P employs Constant-On-Time (COT) control with line feed-forward via the FREQ pin, enabling fast load-step response and simplified loop stability without external compensation. Its internal high-side and low-side MOSFETs operate with dead-time control to prevent shoot-through, and light-load efficiency is enhanced via skip-mode operation with current-modulator-based zero-current detection.

Protection architecture includes cycle-by-cycle over-current limit (16.5A), short-circuit detection (triggered at <50% VREF), output over-voltage (125% VREF) and under-voltage (70% VREF) monitoring, VCC UVLO (4.0V rising threshold), and non-latch thermal shutdown at 150°C with 25°C hysteresis.

Key Specifications

Parameter	Value and Actual Design Meaning
Input Voltage Range	4.5V to 28V - supports wide-rail industrial and computing inputs including 12V and 24V bus systems.
Output Current	8A continuous - sufficient for core logic, GPU I/O, or multi-rail POL applications without external current sharing.
Output Voltage Range	0.8V to 13V - adjustable via resistor divider on FB pin; 1% reference voltage (815mV typ) enables ±1.2% output accuracy.
Internal MOSFET RDS(on)	HS: 30mΩ, LS: 12mΩ - enables high efficiency (>92% at 12V→1.05V/5A) and reduces external component count.
Switching Control	Constant-On-Time (COT) - delivers sub-10μs load transient recovery and eliminates need for Type-II/III compensation networks.
Soft Start	Programmable via SS capacitor - 8.5μA internal charge/discharge current allows precise ramp time control (e.g., 1ms SS = 1nF).
Power Good	Open-drain PGOOD with 90% rising / 85% falling thresholds and 0.5ms + 50% SS delay - provides reliable system sequencing and fault indication.
Thermal Protection	Non-latch shutdown at 150°C with 125°C restart - ensures safe operation under sustained overload or poor PCB thermal design.

Pinout & Package

Package: QFN20 (3mm × 4mm, 0.5mm pitch), exposed thermal pad, RoHS-compliant, lead-free.

Pin/Terminal	Circuit Role	Design Meaning
1 AGND	Analog Ground Reference	Low-noise ground return for feedback and control circuitry; must be separated from PGND in layout.
2 FREQ	Frequency Set Input	Resistor-connected pin that sets ON-time and switching frequency via VIN feed-forward; decoupling with 1nF required.
3 FB	Feedback Input	Monitors output via resistor divider; 815mV reference enables precise output regulation and ramp compensation interface.
4 SS	Soft Start Control	Capacitor-programmed node for controlled output ramp-up/down; 8.5μA internal current source defines timing.
5 EN	Enable Input	Active-high logic input with 1.35V typical threshold and 420mV hysteresis; internal 1MΩ pull-down enables auto-start.
6 PGOOD	Power-Good Output	Open-drain status signal indicating regulated output; requires external pull-up to VCC or system rail.
7 BST	Bootstrap Supply	Connects to SW through 0.1–1μF capacitor to generate floating gate drive for high-side MOSFET.
8,19 IN	Main Input Supply	High-current input pins (4.5–28V); require low-ESR ceramic input capacitors and wide PCB traces/vias.
9,10,17,18 SW	Switch Node	High dv/dt node connecting internal HS/LS MOSFETs to external inductor; demands tight layout and minimal parasitic inductance.
11–16 PGND	Power Ground	High-current return path for output inductor and MOSFETs; must connect directly to thermal pad and minimize impedance.
20 VCC	External Bias Supply	5V external supply required to bias internal circuitry; decoupled with 1μF capacitor close to pin.

Key Features

Feature	Design Value
Proprietary Switching Loss Reduction	Optimizes gate drive timing and dead-time to minimize conduction and switching losses across load range.
External VCC Biasing	Enables independent 5V bias supply, improving light-load efficiency by eliminating internal LDO dropout and quiescent loss.
Programmable Switching Frequency	Set via FREQ resistor; supports 300kHz–1.2MHz range depending on VIN and R_FREQ, enabling EMI optimization and size trade-offs.
Soft Shutdown	Controlled discharge of SS capacitor during disable ensures monotonic output voltage fall, preventing system brown-out glitches.
Ramp Compensation Interface	Dedicated FB node supports external R4/C4 network for stable operation with low-ESR ceramic output capacitors.
Full Fault Protection Suite	Integrated SCP, OCP, OVP, UVP, VCC UVLO, and thermal shutdown - eliminates need for discrete protection ICs in most designs.

Applications

Notebook I/O Power

Networking System POL

Use Scenario: Providing clean, tightly regulated 1.05V/3.3V rails for CPU I/O, chipset, or PCIe switch logic in ultra-thin notebooks.

IC Role / Device Role / Timing Role: Primary synchronous buck regulator with COT control ensuring sub-10μs transient response to burst I/O activity.

Use Value: Eliminates need for external compensation and reduces BOM count while maintaining <±1.2% output accuracy under dynamic load steps.

Use Scenario: Delivering 5V/12V intermediate rails to FPGA transceivers, PHYs, and packet processors in 1U rack-mounted switches.

IC Role / Device Role / Timing Role: High-current POL converter operating in CCM mode with programmable frequency to avoid noise coupling into SerDes lanes.

Use Value: Integrated 30mΩ/12mΩ MOSFETs and QFN20 package enable >93% peak efficiency at 12V→5V/6A, reducing thermal footprint in dense layouts.

Optical Communication Modules

Distributed Power Architecture

Use Scenario: Powering laser diode drivers and TIA amplifiers in SFP+/QSFP modules where low noise and fast transient response are critical.

IC Role / Device Role / Timing Role: Low-noise, high-PSRR buck regulator with AGND/PGND separation and soft-start to prevent optical bias disturbance during hot-plug.

Use Value: 1% reference voltage and PGOOD sequencing ensure stable analog bias before digital initialization, avoiding laser turn-on faults.

Use Scenario: Local point-of-load conversion from 24V backplane to 3.3V/5V for industrial controllers, PLC I/O modules, and sensor hubs.

IC Role / Device Role / Timing Role: Robust, protected buck converter supporting wide input range and operating up to 125°C junction temperature.

Use Value: Full protection suite (OVP/UVP/SCP/thermal) enables unattended operation in harsh environments without external supervision circuitry.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
NB700	Successor device with improved efficiency (94% typ), lower R_DS(on) (22mΩ/9mΩ), and extended temperature range (−40°C to +150°C).	Designed for next-gen high-density POL where thermal margin and efficiency at light load are prioritized.	Select NB700 for new designs requiring longer product lifecycle support and higher reliability in thermally constrained spaces.
NB693A	Pin-compatible replacement with identical QFN20 package, same 8A rating, but updated protection thresholds and reduced quiescent current (30μA vs. 40μA).	Drop-in upgrade path for legacy NB639 designs needing EOL mitigation without PCB redesign.	Choose NB693A when maintaining identical layout and bill-of-materials while achieving RoHS-6 compliance and minor performance refinements.

Compared with NB639DL-LF-P, NB700 offers higher efficiency and extended thermal capability for future-proofing, while NB693A provides seamless pin-and-footprint compatibility with modest improvements in IQ and protection behavior-making it ideal for direct EOL replacement without requalification.

Availability

NB639DL-LF-P is available at Aetrix Electronics and suitable for notebook I/O power, networking POL systems, optical module biasing, and distributed industrial power architectures requiring stable component supply despite end-of-life status.

Supply support for NB639DL-LF-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 NB639 belongs to MPS's high-current synchronous buck converter product line, engineered for compact, high-efficiency DC/DC conversion in space-constrained computing and communications equipment where fast transient response and integrated protection are essential.

FAQ

What does "END OF LIFE, REFER TO NB700 OR NB693A" mean for NB639DL-LF-P?

NB639DL-LF-P is officially discontinued by Monolithic Power Systems. Production has ceased, and no new wafers are being fabricated. While limited inventory may exist, long-term supply is not guaranteed. Engineers should migrate to NB700 (enhanced successor) or NB693A (pin-compatible replacement) for new designs and ongoing production.

Why does NB639DL-LF-P require an external 5V VCC supply?

The NB639DL-LF-P uses an external 5V VCC to bias its internal control circuitry, gate drivers, and protection blocks-separating bias power from the main input rail. This improves light-load efficiency by avoiding LDO dropout losses and enables stable operation across the full 4.5V–28V input range without VCC starvation.

Can NB639DL-LF-P operate without external ramp compensation?

Yes-but only when using output capacitors with sufficient ESR (≥12mΩ), such as POSCAP or polymer types. With low-ESR ceramic capacitors, external ramp compensation (R4/C4 network) is mandatory to ensure stability in PWM mode, as confirmed by slope analysis in the datasheet (VSLOPE1 target: 15–30V/ms).

How is the soft-start time calculated for NB639DL-LF-P?

Soft-start time (T_SS in ms) is determined by T_SS = (C_SS × V_REF) / I_SS, where C_SS is the external capacitor in nF, V_REF = 0.815V, and I_SS = 8.5μA. For example, a 1nF capacitor yields ~96ms soft-start; a 10nF capacitor yields ~960ms.

What is the function of the FREQ pin beyond setting switching frequency?

The FREQ pin implements line feed-forward in the COT control loop: the ON-time is inversely proportional to input voltage (T_ON ∝ 1/V_IN), maintaining near-constant frequency and improving line transient rejection-critical for systems with variable input rails like battery-backed or adapter-sourced supplies.

Does NB639DL-LF-P support forced PWM mode?

No. NB639DL-LF-P automatically transitions between CCM (heavy load) and skip mode (light load) based on inductor current. There is no external pin or register to force continuous PWM operation; light-load efficiency is optimized via this automatic mode switching and current-modulator control.

How does the PGOOD delay scale with soft-start time?

PGOOD rising delay is calculated as T_PGOOD = 0.5 × T_SS + 0.5ms. For a 2ms soft-start, PGOOD asserts after 1.5ms; for a 3ms soft-start, it asserts after 2ms. This ensures PGOOD only goes high after output regulation is fully established and stable.

NB639DL-LF-P Specifications

Product attributes: Attribute value

Manufacturer:: Monolithic Power Systems Inc.

Series:: -

Package/Case:: 20-VFQFN Exposed Pad

Packaging:: Tape & Reel (TR)

Product Status:: Active

Function:: Step-Down

Output Configuration:: Positive

Topology:: Buck

Output Type:: Adjustable

Number of Outputs:: 1

Voltage - Input (Min):: 4.5V

Voltage - Input (Max):: 28V

Voltage - Output (Min/Fixed):: 0.8V

Voltage - Output (Max):: 13V

Current - Output:: 8A

Frequency - Switching:: -

Synchronous Rectifier:: Yes

Operating Temperature:: -40°C ~ 125°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 20-QFN (3x4)

NB639DL-LF-P FAQ

1.How can I place an order for NB639DL-LF-P through Aetrix?

Please submit a Request for Quotation (RFQ) for NB639DL-LF-P on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for NB639DL-LF-P reliable?

The price and inventory of NB639DL-LF-P are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for NB639DL-LF-P is usually 5 days.

3.What payment methods are accepted for NB639DL-LF-P?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for NB639DL-LF-P transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for NB639DL-LF-P?

NB639DL-LF-P orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your NB639DL-LF-P order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for NB639DL-LF-P?

For technical support, including NB639DL-LF-P datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your NB639DL-LF-P requirements.

6.How does Aetrix verify that NB639DL-LF-P is sourced from the original manufacturer or authorized distributors?

All NB639DL-LF-P products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that NB639DL-LF-P meets industry standards.

7.What is the process for return or replacement of NB639DL-LF-P?

All NB639DL-LF-P units undergo pre-shipment inspection (PSI). If there is an issue with NB639DL-LF-P, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The NB639DL-LF-P part is unused and in its original packaging.

Return procedure for NB639DL-LF-P:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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