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

Monolithic Power Systems Inc. NB634EL-LF-Z

Name: NB634EL-LF-Z
Brand: Monolithic Power Systems Inc.
SKU: NB634EL-LF-Z
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: NB634EL-LF-Z

Manufacturer:: Monolithic Power Systems Inc.

Category:: Voltage Regulators - DC DC Switching Regulators

Package:: 14-VFDFN Exposed Pad

Datasheet:: NB634EL-LF-Z.pdf

Description:: IC REG BUCK ADJ 5A 14QFN

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Product details

Overview

NB634EL-LF-Z from Monolithic Power Systems is a synchronous step-down DC/DC converter IC with integrated 120 mΩ high-side and 20 mΩ low-side MOSFETs, delivering 5 A continuous output current across 4.5 V–24 V input range, fixed 500 kHz switching frequency, and adjustable 0.8 V reference output voltage - deployed in notebook I/O power rails and flat-panel display bias supplies.

For engineers reviewing the NB634EL-LF-Z datasheet, NB634EL-LF-Z pinout, NB634EL-LF-Z application, or NB634EL-LF-Z equivalent, key selection criteria include internal MOSFET R_DS(on), latch-off OCP behavior, thermal shutdown threshold (150 °C), and QFN14 (3 mm × 4 mm) package layout constraints for high-current SW and GND routing.

Technical Context

The NB634EL-LF-Z operates in peak current-mode control with internal compensation, enabling stable regulation without external loop components. Its proprietary switching loss reduction technique and bootstrap-driven high-side gate driver support efficient operation up to 90% duty cycle at VIN = 24 V.

It integrates under-voltage lockout (rising threshold 4.0 V, hysteresis 880 mV), soft-start ramp (0–1.2 V), and power-good monitoring (90%/70% V_FB thresholds with 250 μs delay). The EN/SYNC pin enables both enable control and external clock synchronization from 300 kHz to 2 MHz.

Key Specifications

Parameter	Value and Actual Design Meaning
Input Voltage Range	4.5 V to 24 V - supports wide industrial and computing input rails including 12 V and 19 V adapter inputs.
Output Current	5 A continuous - sufficient for CPU core I/O, GPU memory, or LCD panel logic supply without external current boosting.
Switching Frequency	Fixed 500 kHz ±150 kHz - balances EMI filtering complexity and inductor size; sync-capable up to 2 MHz for noise-sensitive designs.
Feedback Reference	0.805 V ±20 mV - sets output voltage via resistor divider; enables precise 1.05 V to 5 V outputs with <1% error at room temperature.
Thermal Shutdown	150 °C junction - latches off until thermal recovery to ~140 °C; protects against sustained overload or poor PCB heatsinking.
OCP Threshold	7 A cycle-by-cycle limit - triggers latch-off when output drops below 70% of V_FB and current exceeds limit, ensuring fault containment.
Package	QFN14 (3 mm × 4 mm, 0.75 mm height) - exposes thermal pad for direct PCB copper connection; requires 14-pin land pattern per JEDEC MO-229 VGED-3.

Pinout & Package

Package: QFN14 (3 mm × 4 mm) with exposed thermal pad (Pin 12/13/GND + Pin 14/AGND); RoHS-compliant, lead-free, moisture sensitivity level 3.

Pin/Terminal	Circuit Role	Design Meaning
1 IN	Input Supply Rail	Accepts 4.5–24 V; requires local 22 µF low-ESR ceramic decoupling capacitor placed adjacent to pins 1 and 12/13.
2–5 SW	Switch Node Output	High-current path connecting internal HS/LS MOSFETs to external inductor; must use wide traces and multiple vias to minimize parasitic inductance.
6 BST	Bootstrap Capacitor Terminal	Connects to SW via 0.1–1 µF ceramic capacitor; powers floating high-side gate driver; optional external diode (e.g., IN4148) improves efficiency at >65% duty cycle.
7 EN/SYNC	Enable & Clock Input	Pull high ≥2 V to enable; pull low ≤0.4 V for shutdown; accepts external 300 kHz–2 MHz clock signal for EMI mitigation.
8 FB	Feedback Input	Senses output voltage via resistor divider; internal 0.805 V reference enables accurate output setting; fold-back frequency reduces switching at light load faults.
9 PG	Power-Good Open-Drain Output	Asserts high after 250 µs when V_FB ≥ 90% of reference; pulls low immediately when V_FB ≤ 70%; drives external enable chains or fault indicators.
10 AAM	Advanced Asynchronous Mode Control	Resistor-divider-set voltage determines transition point between AAM (light-load efficiency) and CCM (full-load stability); optimizes ripple vs. efficiency trade-off.
11 VCC	Bias Regulator Output	Internal 5 V regulator powers control circuitry; requires 0.1 µF ceramic decoupling; supplies bootstrap capacitor charging path.
14 AGND	Analog Ground Reference	Reference node for FB, PG, and error amplifier; must be routed separately from power ground and connected to star point near FB divider.
12, 13, Exposed Pad GND	System Ground & Thermal Path	Low-impedance return for high-current paths (IN, SW, GND); exposed pad must be soldered to large internal/external GND plane for θ_JA = 48 °C/W.

Key Features

Feature	Design Value
Integrated Power Stage	120 mΩ HS + 20 mΩ LS MOSFETs eliminate external switch losses and reduce BOM count by two discrete FETs and drivers.
Internal Compensation	Eliminates need for external Type-II/III compensation network; simplifies design while maintaining phase margin >45° across 1–10 A loads.
Latch-off Overcurrent Protection	Prevents repeated fault cycling during short-circuit events; requires EN or VIN recycle to reset - enhances system reliability in unattended applications.
Sync-Capable Oscillator	EN/SYNC pin accepts external clock from 300 kHz to 2 MHz, enabling synchronized multi-rail systems and deterministic EMI frequency placement.
Bootstrap Charging Architecture	Self-contained floating gate drive with internal UVLO (2.2 V rising threshold) ensures robust high-side switching even at low input voltages.

Applications

Application 1

Application 2

Use Scenario: Notebook motherboard I/O rail supplying USB controller, PCIe switch, and SATA PHY.

IC Role / Device Role / Timing Role: Primary synchronous buck regulator converting 19 V adapter input to 3.3 V/5 V logic supply.

Use Value: Delivers 5 A with <85 mV output ripple at full load using 1 µH inductor and 22 µF ceramic input cap - meets Intel IMVP-7 transient response requirements.

Use Scenario: Flat-panel TV main board powering TCON (timing controller) and LVDS transmitter.

IC Role / Device Role / Timing Role: High-efficiency 12 V-to-1.8 V step-down for display interface logic with tight 1.5% output tolerance.

Use Value: Achieves >92% efficiency at 3 A load and 12 V input; PG signal sequences TCON initialization after 250 µs power stabilization.

Application 3

Application 4

Use Scenario: Digital set-top box SoC core voltage rail requiring dynamic voltage scaling.

IC Role / Device Role / Timing Role: Adjustable-output buck converter controlled via DAC-fed FB divider for adaptive VDD scaling.

Use Value: Supports 0.8–1.35 V output range with <±10 mV line/load regulation; AAM pin enables seamless transition between burst-mode and CCM during DVFS transitions.

Use Scenario: Personal video recorder (PVR) storage subsystem supplying 5 V to dual SATA HDDs.

IC Role / Device Role / Timing Role: High-current 24 V-to-5 V conversion with thermal-aware current limiting for mechanical drive surge currents.

Use Value: Latch-off OCP prevents thermal runaway during HDD spin-up inrush (up to 7 A peak); exposed pad sustains 5 A continuous at 65 °C ambient with 2 oz copper.

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
MP2315DJ-LF-Z	4.5–30 V input, 3 A output, 500 kHz, no AAM pin, smaller QFN8 (2 mm × 2 mm) package.	Lacks latch-off OCP and sync capability; unsuitable for >3 A or fault-critical systems requiring automatic shutdown.	Select when space-constrained and load current ≤3 A; verify thermal performance with reduced copper area.
RT7272BGJ8F	4.5–24 V input, 5 A output, 600 kHz, integrated soft-start, but no PG output or AAM control.	Missing power-good signaling and advanced light-load mode control - limits use in sequenced multi-rail systems.	Choose where PG sequencing is unnecessary and fixed-frequency EMI profile is acceptable; confirm feedback accuracy (±1.5% vs. NB634's ±2.5%).

Compared with MP2315DJ-LF-Z and RT7272BGJ8F, the NB634EL-LF-Z uniquely combines latch-off OCP, EN/SYNC flexibility, and AAM programmability - making it optimal for notebook and display systems demanding fault containment, EMI control, and light-load efficiency tuning.

Availability

NB634EL-LF-Z is available at Aetrix Electronics and suitable for notebook I/O power, flat-panel display bias supplies, digital set-top box SoC rails, and personal video recorder storage subsystems requiring stable component supply and long-term lifecycle support.

Supply support for NB634EL-LF-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, headquartered in Kirkland, WA, with global design and support centers.

The NB634 belongs to MPS's high-current synchronous buck converter product line, designed specifically for compact, high-efficiency DC/DC conversion in space-constrained computing and display applications where thermal performance and fault resilience are critical.

FAQ

What is the recommended input capacitor configuration for NB634EL-LF-Z?

Use a 22 µF X5R/X7R ceramic capacitor placed directly between IN (Pin 1) and GND (Pins 12/13), with additional 0.1 µF ceramic close to the IC for high-frequency decoupling. For electrolytic/tantalum input caps, always add the 0.1 µF ceramic in parallel. RMS current rating must exceed half the maximum load current (≥2.5 A).

Does NB634EL-LF-Z support forced PWM mode, or only auto-mode switching?

The NB634EL-LF-Z does not support forced PWM mode. It operates in automatic mode with Advanced Asynchronous Mode (AAM) at light loads (<100 mA) and transitions to Continuous Conduction Mode (CCM) at higher loads. AAM voltage on Pin 10 sets the transition point - no external PWM signal can override this behavior.

How is thermal performance affected by the exposed pad soldering in QFN14 package?

Full soldering of the exposed thermal pad to a ≥1 cm² internal/external GND plane reduces θ_JA from 48 °C/W to ≤35 °C/W. Inadequate pad connection increases junction temperature by >25 °C at 5 A load, risking premature thermal shutdown. Use ≥6 thermal vias (0.3 mm diameter) under the pad, filled or capped.

Can the NB634EL-LF-Z be synchronized to an external clock while also using the EN function?

Yes - the EN/SYNC pin serves dual purpose. Pulling it above 2 V enables the device; applying a clean CMOS-level clock (300 kHz–2 MHz) while enabled synchronizes the internal oscillator. Ensure clock rise/fall times <50 ns and avoid simultaneous EN toggling during sync operation to prevent metastability.

What happens during startup if the FB voltage rises slower than the internal soft-start ramp?

The internal soft-start ramp (0–1.2 V over ~3 ms) overrides the FB reference until it exceeds 0.805 V. If FB rises slower due to slow RC divider or heavy load, the COMP voltage remains clamped, delaying full regulation. This prevents output overshoot but extends startup time - typical t_start is 4–6 ms with 10 kΩ/8.06 kΩ divider at 1.8 V output.

Is the NB634EL-LF-Z pin-compatible with earlier NB634 variants like NB634EL?

Yes - NB634EL-LF-Z shares identical pinout, electrical characteristics, and thermal pad layout with NB634EL and NB634EL-Z. The "LF" suffix denotes RoHS-compliant lead-free finish; "Z" indicates tape-and-reel packaging. All share the same QFN14 (3 mm × 4 mm) footprint and land pattern.

Why is NB634 marked "NOT RECOMMENDED FOR NEW DESIGNS"?

MPS issued this notice because newer-generation converters (e.g., MP2451, MPQ4571) offer improved efficiency (>95%), lower quiescent current (<100 µA), and enhanced protection features. However, NB634EL-LF-Z remains fully qualified, in active production, and supported for legacy design refreshes and long-lifecycle industrial programs.

NB634EL-LF-Z Specifications

Product attributes: Attribute value

Manufacturer:: Monolithic Power Systems Inc.

Series:: -

Package/Case:: 14-VFDFN 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):: 24V

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

Voltage - Output (Max):: 21.6V

Current - Output:: 5A

Frequency - Switching:: 500kHz

Synchronous Rectifier:: Yes

Operating Temperature:: -20°C ~ 85°C (TA)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 14-QFN (3x4)

NB634EL-LF-Z FAQ

1.How can I place an order for NB634EL-LF-Z through Aetrix?

Please submit a Request for Quotation (RFQ) for NB634EL-LF-Z 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 NB634EL-LF-Z reliable?

The price and inventory of NB634EL-LF-Z are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for NB634EL-LF-Z is usually 5 days.

3.What payment methods are accepted for NB634EL-LF-Z?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for NB634EL-LF-Z transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for NB634EL-LF-Z?

NB634EL-LF-Z orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your NB634EL-LF-Z 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 NB634EL-LF-Z?

For technical support, including NB634EL-LF-Z datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your NB634EL-LF-Z requirements.

6.How does Aetrix verify that NB634EL-LF-Z is sourced from the original manufacturer or authorized distributors?

All NB634EL-LF-Z 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 NB634EL-LF-Z meets industry standards.

7.What is the process for return or replacement of NB634EL-LF-Z?

All NB634EL-LF-Z units undergo pre-shipment inspection (PSI). If there is an issue with NB634EL-LF-Z, 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 NB634EL-LF-Z part is unused and in its original packaging.

Return procedure for NB634EL-LF-Z:

1.Submit a request within 90 days.

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

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