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

Monolithic Power Systems Inc. NB621EV-LF-P

Name: NB621EV-LF-P
Brand: Monolithic Power Systems Inc.
SKU: NB621EV-LF-P
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: NB621EV-LF-P

Manufacturer:: Monolithic Power Systems Inc.

Category:: Voltage Regulators - Linear + Switching

Package:: 28-VFQFN Exposed Pad

Datasheet:: NB621EV-LF-P.pdf

Description:: IC REG DL BUCK/LNR 600KHZ 28QFN

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Product details

Overview

NB621EV-LF-P from Monolithic Power Systems is a synchronous step-down DC/DC converter with integrated high-side MOSFET and 100mA LDO regulator, delivering up to 8A continuous output current across 5.5V–25V input range, fixed 600kHz switching frequency, and adjustable output voltage from 0.8V to 15V - deployed in notebook I/O power and flat-panel TV main power rails.

For engineers reviewing the NB621EV-LF-P datasheet, NB621EV-LF-P pinout, NB621EV-LF-P application, or NB621EV-LF-P equivalent, key selection criteria include its dual-regulator architecture (buck + LDO), thermal shutdown at 150°C, power-good output with 0.42×soft-start delay, and QFN28 (4mm×5mm) package with exposed thermal pad for high-current thermal management.

Technical Context

The NB621 operates in peak-current-mode control with internal compensation, enabling fast transient response and simplified loop stability without external Type-II/III networks. Its oscillator supports synchronization from 300kHz to 2MHz via the EN/SYNC pin, while fold-back frequency reduction below 400mV FB voltage prevents current-limit runaway during short-circuit faults.

It integrates two independent regulation paths: a primary synchronous buck stage with 50mΩ high-side R_DS(on) and an auxiliary LDO with selectable 3.3V/5V output (via SELH), switchable to pass-through mode via REGO when buck output is valid - enabling seamless power sequencing in multi-rail systems.

Key Specifications

Parameter	Value and Actual Design Meaning
Input Voltage Range	5.5V to 25V - supports wide industrial and computing input rails including 12V and 19V adapter inputs.
Continuous Output Current	8A - delivered by integrated high-side MOSFET with 50mΩ R_DS(on), enabling compact single-chip solutions for high-current point-of-load applications.
Switching Frequency	Fixed 600kHz - balances efficiency and size; externally synchronizable from 300kHz to 2MHz for EMI mitigation in noise-sensitive systems.
LDO Output Options	Selectable 3.3V or 5V (±2.5% accuracy) - configured via SELH pin; delivers 100mA with 5Ω typical R_DS(on) for auxiliary bias rails.
Feedback Reference Voltage	0.808V ±20mV - sets output voltage via external resistor divider; enables precise low-voltage regulation down to 0.8V.
Thermal Shutdown Threshold	150°C - protects die under overload or poor PCB thermal design; auto-recovery at ~140°C hysteresis.
Power Good Accuracy	±10% of V_FB - PG asserts when output reaches 90% of target and de-asserts at 70%, with 20µs fault delay for clean system monitoring.

Pinout & Package

Package: 4mm × 5mm, 28-pin QFN with exposed thermal pad (JEDEC MO-220 VHGD-3 compliant); requires solder paste stencil aperture matching land pattern per datasheet Figure 14.

Pin/Terminal	Circuit Role	Design Meaning
1 (BST)	Bootstrap supply node	Connects external capacitor between SW and BST to generate floating gate drive voltage for high-side MOSFET driver.
2–5 (SW)	Switch node	High-current output of synchronous rectifier; requires wide copper traces and multiple vias for 8A peak current handling.
7, 10, 23 (GND / AGND)	System and analog ground	GND is power return path; AGND is isolated reference for feedback and error amplifier - must be star-connected near IC.
11 (VCC)	Bias supply rail	Internal 5V regulator output; decoupled with 1µF ceramic capacitor to stabilize gate drivers and analog circuitry.
14 (FB)	Voltage feedback input	Senses output via resistor divider; internal 0.808V reference enables precise output programming from 0.8V to 15V.
15 (PG)	Power-good open-drain output	Signals valid regulation (high) or fault (low); used for sequencing enable/disable of downstream rails or microcontroller reset assertion.
16 (EN/SYNC)	Enable and clock sync input	Pull ≥2V to enable; apply external 300kHz–2MHz clock to synchronize switching and reduce EMI beat frequencies.
22 (SELH)	LDO voltage select	Ground = 5V LDO output; pull ≥2.5V = 3.3V LDO output - enables dual-rail flexibility without external regulators.
23 (ENLDO)	LDO enable control	High = enable integrated LDO; low = disable LDO independently of main buck regulator.
25 (LDO)	LDO output terminal	Delivers regulated 3.3V or 5V; requires 10µF ceramic decoupling capacitor placed adjacent to pin for stability and transient response.
26 (REGO)	LDO source selector	Connects LDO input to buck output when valid - allows LDO to operate from higher-efficiency buck rail instead of VIN.

Key Features

Feature	Design Value
Integrated high-side MOSFET	50mΩ R_DS(on) enables 8A output without external switches - reduces BOM count and layout complexity in space-constrained designs.
Synchronous rectification	Eliminates external Schottky diode; improves full-load efficiency by >5% vs. asynchronous topology at 12V_IN/5V_OUT.
Internal compensation network	Removes need for external Type-II/III compensation components - simplifies design validation and reduces footprint by ≥3 passive parts.
Power-good (PG) with delay	0.42× soft-start time delay ensures PG only asserts after output settles - prevents false system resets during startup transients.
Hiccup-mode overcurrent protection	Enters periodic restart on sustained short-circuit - limits average fault current and junction temperature rise, enhancing reliability.

Applications

Notebook I/O Power

Flat Panel TV Main Rail

Use Scenario: Supplies 5V or 12V to USB controllers, card readers, and display interface logic in ultrabooks and 2-in-1 platforms.

IC Role / Device Role / Timing Role: Primary buck regulator with integrated LDO powering auxiliary circuits; sequenced via ENLDO and PG signals.

Use Value: Eliminates discrete LDO and external MOSFET drivers - reduces solution size by 35% versus discrete buck+LDO implementation.

Use Scenario: Generates 12V main logic rail and 3.3V MCU core supply in LCD/LED TV power boards.

IC Role / Device Role / Timing Role: Dual-output regulator: buck stage powers backlight drivers and TCON; LDO supplies SoC standby domain.

Use Value: SELH and REGO pins enable dynamic LDO sourcing - improves light-load efficiency by 12% vs. fixed-VIN LDO operation.

Distributed Networking Power

Personal Video Recorder (PVR) Board

Use Scenario: Powers FPGA I/O banks and PHY interfaces in 1U rack-mounted switches with 12V backplane input.

IC Role / Device Role / Timing Role: High-current POL regulator with sync capability - synchronized to system clock to suppress conducted EMI in dense board layouts.

Use Value: 600kHz base frequency + 300kHz–2MHz sync range meets CISPR-32 Class B emissions limits without added shielding.

Use Scenario: Delivers 5V/3A to HDD controller and 3.3V/100mA to tuner demodulator in set-top box PVR modules.

IC Role / Device Role / Timing Role: Single-package solution replacing two separate regulators - simplifies thermal design and reduces layer count.

Use Value: Integrated bootstrap diode and internal LDO eliminate 4 external components - cuts assembly cost by $0.18/unit at volume.

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous buck + integrated LDO applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
NB700	Successor device with 10A rating, 2.5V–24V input, and improved 30mΩ R_DS(on); supports programmable soft-start and enhanced thermal metrics.	Designed for next-gen notebooks and AI edge modules requiring higher current density and lower thermal resistance (θ_JA = 32°C/W).	Select NB700 for new designs targeting >8A loads or tighter thermal budgets; pin-compatible but requires updated layout for thermal pad and BST cap.
NB693A	Lower-cost variant with 6A rating, 4.5V–24V input, no integrated LDO - requires external 3.3V/5V regulator for auxiliary rails.	Targeted at cost-sensitive consumer electronics where auxiliary LDO is implemented separately or omitted.	Choose NB693A only if LDO integration is unnecessary and 6A output suffices; not drop-in due to missing LDO pins (SELH, ENLDO, LDO, REGO).

Compared with NB621EV-LF-P, NB700 offers higher current and better thermal performance but requires layout revision, while NB693A sacrifices LDO integration and output current to reduce BOM cost - making NB621 the optimal balance for legacy designs needing dual-rail integration in minimal area.

Availability

NB621EV-LF-P is available at Aetrix Electronics and suitable for notebook I/O power, flat-panel TV main rail, and distributed networking power applications requiring stable component supply amid end-of-life transitions.

Supply support for NB621EV-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 mixed-signal ICs for power management, motion control, and automotive applications.

The NB621 belongs to MPS's NB-series high-current synchronous buck converters, designed specifically for space-constrained computing and consumer electronics requiring integrated power delivery with minimal external components.

FAQ

What does "END OF LIFE, REFER TO NB700 OR NB693A" mean for NB621EV-LF-P?

This designation indicates Monolithic Power Systems has discontinued active development and long-term production of NB621EV-LF-P. It remains available through authorized distributors like Aetrix Electronics for legacy program support, but new designs should migrate to NB700 (feature-enhanced successor) or NB693A (cost-optimized alternative), both of which share functional overlap in buck regulation but differ in LDO integration and current capability.

Can NB621EV-LF-P operate without an external bootstrap capacitor?

No. Pin 1 (BST) requires an external capacitor (0.1µF–1µF) connected between BST and SW to generate the floating gate-drive voltage for the internal high-side MOSFET. Omitting this capacitor disables the high-side switch, causing immediate failure or unregulated output. The datasheet specifies ceramic X5R/X7R types with low ESR and tight tolerance for reliable bootstrapping across temperature.

How is the LDO output voltage selected between 3.3V and 5V?

Voltage selection is controlled by the SELH pin (Pin 22): grounding SELH configures the LDO for 5V output (±2.5%); pulling SELH to ≥2.5V (e.g., via resistor divider from VIN or VCC) selects 3.3V output (±2.5%). This is a hardware-configured, non-volatile setting - no I²C or digital interface is involved. ENLDO (Pin 23) independently enables or disables the LDO regardless of SELH state.

What is the purpose of the REGO pin, and when should it be used?

REGO (Pin 26) connects the LDO's input to the main buck regulator's output instead of VIN, allowing the LDO to draw power from the more efficient buck rail once it's stable. This improves light-load efficiency by avoiding LDO dropout losses from high VIN. Use REGO when the buck output voltage exceeds the LDO's required input headroom (e.g., 5V buck output feeding a 3.3V LDO), and tie REGO directly to the buck output node.

Does NB621EV-LF-P support forced PWM mode, or does it automatically enter discontinuous conduction mode (DCM) at light load?

NB621EV-LF-P operates exclusively in forced continuous conduction mode (FCCM) - it does not auto-shift to DCM or pulse-frequency modulation (PFM). The AAM pin (Pin 12) allows optional non-synchronous operation under light load via external resistor dividers, but the default configuration (AAM grounded) maintains synchronous rectification across all load conditions, ensuring predictable EMI profile and output ripple behavior.

Is the PG (Power Good) signal actively driven or open-drain, and what external pull-up is required?

PG (Pin 15) is an open-drain output requiring an external pull-up resistor to a valid logic rail (e.g., 3.3V or 5V). Typical values range from 10kΩ to 100kΩ. When the output voltage reaches ≥90% of the programmed value, PG pulls high via the external resistor; during undervoltage or startup, it remains low. The 20µs delay on PG de-assertion prevents chatter during brief line transients.

What thermal derating applies to the 8A output current rating?

The 8A rating is specified at T_A = +25°C with proper PCB copper area (4-layer JEDEC standard). Derating begins above +25°C ambient: at +85°C ambient, maximum continuous current drops to ~5.2A (based on θ_JA = 40°C/W and T_J(MAX) = 150°C). Layout with 2oz copper, thermal vias under the exposed pad, and airflow improves real-world current capacity by up to 1.8A at +85°C.

NB621EV-LF-P Specifications

Product attributes: Attribute value

Manufacturer:: Monolithic Power Systems Inc.

Series:: -

Package/Case:: 28-VFQFN Exposed Pad

Packaging:: Tape & Reel (TR)

Product Status:: Active

Topology:: Step-Down (Buck) (1), Linear (LDO) (1)

Number of Outputs:: 2

Frequency - Switching:: 600kHz

Voltage/Current - Output 1:: 0.8V ~ 15V, 8A

Voltage/Current - Output 2:: 3V/5V, 100mA

Voltage/Current - Output 3:: -

w/LED Driver:: No

w/Supervisor:: No

w/Sequencer:: No

Voltage - Supply:: 5.5V ~ 25V

Operating Temperature:: -20°C ~ 85°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 28-QFN (4x5)

NB621EV-LF-P FAQ

1.How can I place an order for NB621EV-LF-P through Aetrix?

Please submit a Request for Quotation (RFQ) for NB621EV-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 NB621EV-LF-P reliable?

The price and inventory of NB621EV-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 NB621EV-LF-P is usually 5 days.

3.What payment methods are accepted for NB621EV-LF-P?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for NB621EV-LF-P transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for NB621EV-LF-P?

NB621EV-LF-P orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your NB621EV-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 NB621EV-LF-P?

For technical support, including NB621EV-LF-P datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your NB621EV-LF-P requirements.

6.How does Aetrix verify that NB621EV-LF-P is sourced from the original manufacturer or authorized distributors?

All NB621EV-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 NB621EV-LF-P meets industry standards.

7.What is the process for return or replacement of NB621EV-LF-P?

All NB621EV-LF-P units undergo pre-shipment inspection (PSI). If there is an issue with NB621EV-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 NB621EV-LF-P part is unused and in its original packaging.

Return procedure for NB621EV-LF-P:

1.Submit a request within 90 days.

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

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