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Analog Devices Inc. LTC3851EUD#PBF
- Part No.:
- LTC3851EUD#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LTC3851EUD#PBF.pdf
- Description:
- IC REG CTRLR BUCK 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:1,332
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Product details
Overview
LTC3851EUD#PBF from Analog Devices (formerly Linear Technology) is a high-performance synchronous step-down switching regulator controller driving dual N-channel MOSFETs in constant-frequency current-mode operation. It supports 4V–38V input, delivers 0.8V–5.5V output with ±1% accuracy, operates up to 750kHz, and features OPTI-LOOP® compensation, adjustable soft-start via TK/SS pin, and selectable light-load modes (Burst, Pulse-Skip, or Continuous). It is used in telecom power supplies requiring high efficiency and tight regulation under wide load transients.
For engineers reviewing the LTC3851EUD#PBF datasheet, LTC3851EUD#PBF pinout, LTC3851EUD#PBF application, or LTC3851EUD#PBF equivalent, key selection criteria include its 16-pin 3mm × 3mm QFN package with exposed thermal pad, RSENSE/DCR current sensing flexibility, phase-lockable oscillator, 0.8V reference tolerance, and integrated 5V INTVCC regulator - all critical for compact, high-density DC/DC designs in industrial and communications infrastructure.
Technical Context
The LTC3851EUD#PBF implements a constant-frequency current-mode control architecture with a transconductance error amplifier (gm = 2 mmho, GBW = 3 MHz) and precision 0.8V feedback reference (±1% over temperature). Its ITH pin serves as both error amplifier output and current threshold control point, enabling dynamic peak-current adjustment across load conditions.
It integrates dual gate drivers (TG/BG) with matched 25ns rise/fall times, 30ns dead-time control, and on-resistance specs (TG RUP = 2.6Ω, BG RDOWN = 1.1Ω), supporting efficient high-side and low-side N-MOSFET switching. The MODE/PLLIN pin enables mode selection (Burst/Pulse-Skip/Continuous) or external clock synchronization, while FREQ/PLLFLTR sets oscillator frequency from 250kHz to 750kHz via resistor programming.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 38V - supports wide-range industrial and telecom inputs without pre-regulation. |
| Output Voltage Accuracy | ±1% at VFB - ensures stable 0.8V reference tracking for precise output regulation. |
| Switching Frequency | 250kHz to 750kHz - adjustable via FREQ/PLLFLTR resistor; higher frequencies reduce passive size, lower frequencies improve efficiency. |
| Light-Load Operation | Selectable Burst Mode®, Pulse-Skipping, or Continuous Conduction - enables >90% efficiency at 10mA load in Burst Mode. |
| Current Sensing | RSENSE or DCR-based - eliminates need for power-wasting sense resistors in high-current applications. |
| Internal Regulator | 5V INTVCC with ±2% load regulation - powers gate drivers and internal circuitry independently of VIN. |
| Shutdown Current | 20μA - enables ultra-low-power standby in battery-backed or energy-sensitive systems. |
Pinout & Package
Package: 16-lead (3mm × 3mm) plastic QFN with exposed thermal pad (Pin 17 = GND), rated for –40°C to +85°C operating temperature.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| RUN (Pin 1) | Enable control input | Logic-high (>1.25V) enables operation; internal 2μA pull-up allows simple RC startup sequencing. |
| TK/SS (Pin 2) | Soft-start/tracking input | 1μA internal current charges external capacitor to ramp VOUT linearly; supports ratiometric tracking of master supply. |
| ITH (Pin 3) | Error amp output / current threshold | Directly sets peak inductor current; voltage range 0.4V–1.6V determines current limit and loop dynamics. |
| FB (Pin 4) | Feedback input | Compares output divider voltage to 0.8V reference; ±50nA bias current minimizes divider error. |
| SENSE– (Pin 5) | Current sense inverting input | High-impedance node (±1μA bias) for DCR or resistor-based sensing networks. |
| SENSE+ (Pin 6) | Current sense non-inverting input | Accepts common-mode voltage up to 5.5V; enables accurate sensing across full duty cycle range. |
| ILIM (Pin 7) | Current limit select | Tied to GND/FLOAT/INTVCC to set max sense threshold at 30mV/50mV/75mV - configures overcurrent protection level. |
| GND (Pin 8) | Analog/digital ground | Kelvin connection point for CVCC, CIN, and compensation components to minimize noise coupling. |
| BG (Pin 9) | Bottom gate driver output | Drives low-side N-MOSFET gate between GND and INTVCC; 1.1Ω pull-down ensures fast turn-off. |
| INTVCC (Pin 10) | Internal 5V regulator output | Supplies gate drivers and core logic; requires ≥2.2μF low-ESR ceramic decoupling to GND. |
| VIN (Pin 11) | Main input supply | Primary power path for INTVCC LDO and high-voltage circuitry; decouple locally with bulk + ceramic capacitors. |
| BOOST (Pin 12) | Floating bootstrap supply | Charges external bootstrap capacitor during low-side conduction; swings from ~VIN to VIN+INTVCC. |
| TG (Pin 13) | Top gate driver output | Floating driver referenced to SW node; 2.6Ω pull-up supports fast high-side MOSFET turn-on. |
| SW (Pin 14) | Switch node | Connects to inductor and external Schottky diode cathode; voltage swings from ~–0.3V to VIN. |
| FREQ/PLLFLTR (Pin 16) | Oscillator/PLL filter | Resistor-to-GND sets frequency; RC network enables PLL lock when external clock applied to MODE/PLLIN. |
| MODE/PLLIN (Pin 15) | Mode select / sync input | Selects Burst/Pulse-Skip/Continuous mode or accepts external clock (250–750kHz) for forced sync operation. |
Key Features
| Feature | Design Value |
|---|---|
| OPTI-LOOP® Compensation | Minimizes required output capacitance by optimizing transient response across wide ESR/capacitance ranges - reduces BOM count and board area. |
| Dual N-MOSFET Drive | Integrated high- and low-side drivers eliminate need for external driver ICs - simplifies layout and improves timing control. |
| Adjustable Output Soft-Start | Programmable ramp rate via TK/SS capacitor prevents inrush current and output overshoot during power-up. |
| Output Overvoltage Protection | Hardware comparator triggers immediate top-FET shutdown and bottom-FET activation if VFB exceeds 0.88V - protects downstream loads without software delay. |
| Very Low Dropout Operation | 99% duty cycle capability enables regulation down to VOUT ≈ VIN − 0.3V - critical for high-VIN, low-VOUT applications like 12V-to-1.2V conversion. |
Applications
| Telecom Power Supply | Industrial PLC Module |
|---|---|
Use Scenario: 48V backplane-to-3.3V/5V conversion in carrier-grade line cards with strict ripple and transient requirements. IC Role / Device Role / Timing Role: Primary synchronous buck controller regulating intermediate bus voltage with phase-lockable 500kHz switching to avoid spectral interference with data lanes. Use Value: OPTI-LOOP® compensation maintains <1% output deviation during 10A step loads; 20μA shutdown IQ extends system standby time. | Use Scenario: Distributed 24V-to-5V/3.3V power for I/O modules in harsh factory environments with wide ambient temperature swings. IC Role / Device Role / Timing Role: High-reliability step-down controller with DCR current sensing to eliminate sense resistor losses and improve thermal margin. Use Value: RSENSE/DCR flexibility enables >94% efficiency at full load; –40°C to +85°C rating ensures operation in uncooled enclosures. |
| Automotive Infotainment Head Unit | Network Switch Midplane |
Use Scenario: 12V battery-derived 1.2V/1.8V CPU core supply with tight regulation and low EMI in space-constrained dashboard electronics. IC Role / Device Role / Timing Role: Synchronous buck controller using Burst Mode® to maintain >85% efficiency at 10mA idle current while suppressing audible noise. Use Value: Selectable light-load modes eliminate coil whine; 3mm × 3mm QFN package fits dense PCB layouts near SoC. | Use Scenario: 48V-to-12V intermediate conversion feeding multiple downstream POL regulators in 1U rack-mounted switches. IC Role / Device Role / Timing Role: High-efficiency primary controller with 750kHz operation to shrink magnetics and support high-density board stacking. Use Value: 99% duty cycle supports 48V-to-12V conversion with minimal dropout loss; exposed thermal pad enables 68°C/W θJA for reliable 15A operation. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar synchronous buck controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3851EMSE#PBF | Same die, 16-lead MSOP package with θJA = 40°C/W; no exposed thermal pad. | Suitable for lower-power designs (<10A) where thermal budget allows larger footprint. | Choose for legacy MSOP-compatible layouts or when QFN reflow process is unavailable. |
| LTC3851-1EUD#PBF | Identical functionality except replaces adjustable ILIM with power-good (PGOOD) output signal. | Required where system-level power sequencing or fault reporting is needed instead of programmable current limiting. | Choose when PGOOD assertion is mandatory for host processor boot validation. |
Compared with LTC3851EMSE#PBF, the LTC3851EUD#PBF offers superior thermal performance (68°C/W vs 40°C/W) in a smaller footprint, enabling higher current density; compared with LTC3851-1EUD#PBF, it retains flexible current-limit configuration at the cost of omitting PGOOD - making it ideal for designs prioritizing overcurrent adaptability over status signaling.
Availability
LTC3851EUD#PBF is available at Aetrix Electronics and suitable for telecom power supplies, industrial PLC modules, and automotive infotainment systems requiring stable component supply, long-term lifecycle support, and guaranteed RoHS-compliant manufacturing.
Supply support for LTC3851EUD#PBF 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
Analog Devices, Inc. (ADI) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, formed through the acquisition of Linear Technology in 2017.
The LTC3851 series belongs to ADI's high-efficiency DC/DC controller product line, designed specifically for demanding intermediate bus and point-of-load applications in telecom, industrial, and automotive systems where precision regulation, thermal robustness, and flexible light-load operation are essential.
FAQ
What is the maximum supported switching frequency for the LTC3851EUD#PBF?
The LTC3851EUD#PBF supports a phase-lockable fixed-frequency range from 250kHz to 750kHz. The upper limit of 750kHz is achieved when the FREQ/PLLFLTR pin is tied to GND with a 36kΩ resistor. This high-frequency capability allows designers to minimize inductor and capacitor sizes in space-constrained applications while maintaining stable current-mode control. The LTC3851EUD#PBF maintains full functionality-including OPTI-LOOP® compensation and accurate current sensing-across the entire range.
How does the ILIM pin configure current limiting on the LTC3851EUD#PBF?
The ILIM pin on the LTC3851EUD#PBF is a tri-level logic input that selects the maximum current sense threshold: 30mV when tied to GND, 50mV when left floating, and 75mV when connected to INTVCC. This directly sets the peak inductor current trip point for overcurrent protection and foldback limiting. The LTC3851EUD#PBF uses this threshold in conjunction with the sensed voltage across RSENSE or the DCR network to determine MOSFET turn-off timing, ensuring consistent short-circuit response across operating conditions.
Can the LTC3851EUD#PBF operate with an input voltage below 4V?
No, the LTC3851EUD#PBF has a specified minimum input voltage of 4V per its Absolute Maximum Ratings and Electrical Characteristics tables. Operation below 4V violates the guaranteed operating range and may result in undervoltage lockout (UVLO) activation, where the INTVCC regulator disables at ~3.25V. While the device might exhibit marginal behavior near 3.8V under specific conditions, the LTC3851EUD#PBF is not characterized or warranted for reliable operation below 4V, and system designs must respect this lower bound.
What is the purpose of the exposed thermal pad on the LTC3851EUD#PBF QFN package?
The exposed thermal pad (Pin 17) on the LTC3851EUD#PBF is electrically and thermally connected to GND and must be soldered to a PCB copper pour to achieve the specified θJA of 68°C/W. This pad provides the primary thermal conduction path from the die to the board, significantly improving power dissipation capability and junction temperature stability under continuous high-current operation. Failure to solder the pad results in degraded thermal performance and potential reliability issues. The LTC3851EUD#PBF datasheet explicitly requires this connection for compliance with its rated specifications.
Does the LTC3851EUD#PBF support output voltage tracking during startup?
Yes, the LTC3851EUD#PBF supports ratiometric output voltage tracking via the TK/SS pin. By connecting an external resistor divider from a master supply to the TK/SS pin, the LTC3851EUD#PBF regulates its FB pin to match the rising voltage at TK/SS rather than the internal 0.8V reference - enabling coordinated startup with other rails. This feature is confirmed in the Applications Information section and functional diagram, and is distinct from simple soft-start, as it maintains proportional relationship throughout the ramp. The LTC3851EUD#PBF implements this using an internal 1μA current source and comparator architecture that actively follows the TK/SS voltage trajectory.
LTC3851EUD#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-WFQFN Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- 4V ~ 38V
- Frequency - Switching:
- 250kHz ~ 750kHz
- Duty Cycle (Max):
- 99%
- Synchronous Rectifier:
- Yes
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Current Limit, Enable, Frequency Control, Soft Start, Tracking
- Operating Temperature:
- -40°C ~ 85°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-QFN (3x3)
LTC3851EUD#PBF FAQ
1.How can I place an order for LTC3851EUD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3851EUD#PBF 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 LTC3851EUD#PBF reliable?
The price and inventory of LTC3851EUD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3851EUD#PBF is usually 5 days.
3.What payment methods are accepted for LTC3851EUD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3851EUD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3851EUD#PBF?
LTC3851EUD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3851EUD#PBF 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 LTC3851EUD#PBF?
For technical support, including LTC3851EUD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3851EUD#PBF requirements.
6.How does Aetrix verify that LTC3851EUD#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3851EUD#PBF 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 LTC3851EUD#PBF meets industry standards.
7.What is the process for return or replacement of LTC3851EUD#PBF?
All LTC3851EUD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3851EUD#PBF, 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 LTC3851EUD#PBF part is unused and in its original packaging.
Return procedure for LTC3851EUD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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