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Analog Devices Inc. LTC3851IUD#PBF
- Part No.:
- LTC3851IUD#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LTC3851IUD#PBF.pdf
- Description:
- IC REG CTRLR BUCK 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:104
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Product details
Overview
LTC3851IUD#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 topology. It operates from 4V to 38V input, delivers 0.8V–5.5V output with ±1% accuracy, supports phase-lockable 250kHz–750kHz switching, and features OPTI-LOOP® compensation for optimized transient response in telecom power supplies.
For engineers reviewing the LTC3851IUD#PBF datasheet, LTC3851IUD#PBF pinout, LTC3851IUD#PBF application, or LTC3851IUD#PBF equivalent, key selection criteria include its 16-pin 3mm × 3mm QFN package with exposed thermal pad, selectable light-load modes (Burst/Pulse-Skip/Continuous), RSENSE or DCR current sensing, and integrated 5V INTVCC regulator for gate drive.
Technical Context
The LTC3851IUD#PBF implements a constant-frequency current-mode control architecture with a transconductance error amplifier (gm = 2 mmho, GBW = 3 MHz) and precision 0.8V reference (±1% over –40°C to 125°C). Its ITH pin serves as both error amplifier output and current threshold control point, enabling direct regulation of peak inductor current via feedback loop dynamics.
Phase-locked loop synchronization is achieved through the MODE/PLLIN pin accepting external clocks (250–750 kHz), while FREQ/PLLFLTR sets nominal frequency via resistor programming. The IC integrates anti-shoot-through logic, dropout detection with forced top-FET off cycles, and output overvoltage protection triggered at 0.86–0.90V on VFB.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 38V - supports wide-range industrial and telecom DC inputs without pre-regulation |
| Output Voltage Accuracy | ±1% - ensures stable rail generation for sensitive digital loads like FPGAs and ASICs |
| Switching Frequency | 250kHz to 750kHz - adjustable via resistor or PLL sync for EMI optimization and inductor size trade-offs |
| Reference Voltage | 0.8V ±1% - enables precise low-voltage outputs down to 0.8V with minimal headroom loss |
| Light-Load Modes | Burst Mode®, Pulse-Skipping, Continuous - selectable via MODE/PLLIN for efficiency vs. ripple/noise trade-off |
| Current Sensing | RSENSE or DCR - supports high-efficiency inductor-based sensing or accurate discrete resistor methods |
| Thermal Package | 16-pin 3mm × 3mm QFN with exposed GND pad - θJA = 68°C/W, suitable for compact high-power density designs |
Pinout & Package
Package: 16-lead (3mm × 3mm) plastic QFN with exposed thermal pad (Pin 17 = GND, must be soldered to PCB). Thermal resistance θJA = 68°C/W, θJC = 4.2°C/W. Operating junction temperature range: –40°C to 125°C.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| RUN | Enable control input | Active-high enable with 1.10–1.35V threshold; internal 2μA pull-up allows simple RC startup sequencing |
| TK/SS | Soft-start/tracking input | 1μA internal charge current ramps voltage to control VOUT rise time or track master supply |
| ITH | Error amp output / current threshold | Directly sets peak inductor current; also used for loop compensation network connection |
| VFB | Feedback input | Compares output divider voltage to 0.8V reference; supports remote sensing for load regulation |
| SENSE+ / SENSE– | Differential current sense inputs | High-impedance inputs (±1μA bias) for RSENSE or DCR networks; common-mode range 0–5.5V |
| ILIM | Current limit select | Tri-level input (GND/FLOAT/INTVCC) sets max sense threshold to 30/50/75mV for scalable overcurrent protection |
| MODE/PLLIN | Mode select / sync input | Selects Burst/Pulse-Skip/Continuous mode or accepts external clock for PLL synchronization |
| FREQ/PLLFLTR | Oscillator programming / PLL filter | Resistor-to-GND sets frequency; RC network provides PLL loop filtering when synchronized |
| TG / BG | Top/bottom gate drivers | Drives N-MOSFET gates with 2.6Ω/1.5Ω pull-up and 2.4Ω/1.1Ω pull-down; 25ns transition times |
| SW / BOOST / VIN / INTVCC / GND | Power path connections | SW connects to inductor node; BOOST supplies floating TG driver; INTVCC = regulated 5V output for internal logic |
Key Features
| Feature | Design Value |
|---|---|
| OPTI-LOOP® Compensation | Minimizes required output capacitance by optimizing loop stability across wide COUT/ESR ranges |
| Adjustable Current Limit | Three programmable thresholds (30/50/75mV) via ILIM pin enable precise overcurrent protection scaling |
| 99% Duty Cycle Operation | Enables very low dropout regulation - critical for high-VIN, low-VOUT applications like 12V-to-1.2V conversion |
| Low Shutdown IQ | 20μA shutdown current reduces system standby power - essential for always-on telecom equipment |
| Output Overvoltage Protection | Hardware comparator triggers at 0.86–0.90V on VFB, forcing BG on and TG off to clamp overshoot |
Applications
| Telecom Power Supply | Industrial FPGA Core Rail |
|---|---|
Use Scenario: Generating 1.2V/15A core voltage for Xilinx Kintex-7 FPGA in 48V intermediate bus architecture. IC Role / Device Role / Timing Role: Primary synchronous buck controller regulating tightly-toleranced low-voltage rail with fast load-step response. Use Value: ±1% output accuracy and OPTI-LOOP® ensure stable operation under dynamic logic switching; 750kHz switching enables compact 0.68μH inductor. | Use Scenario: Point-of-load converter powering ARM Cortex-A9 processor in ruggedized factory automation controller. IC Role / Device Role / Timing Role: High-reliability step-down controller operating across –40°C to 125°C ambient with thermal pad soldering. Use Value: 125°C rated QFN package and guaranteed specs over full temp range eliminate derating concerns in sealed enclosures. |
| Distributed DC Power System | Automotive Infotainment Head Unit |
Use Scenario: Secondary 3.3V/10A rail derived from 24V vehicle battery in data center rack power shelf. IC Role / Device Role / Timing Role: Isolated secondary-side controller managing high-current distribution with RSENSE sensing. Use Value: RSENSE or DCR flexibility allows optimal trade-off between sensing accuracy and conduction losses in multi-kW systems. | Use Scenario: 5V USB-C PD power delivery subsystem in automotive infotainment display module. IC Role / Device Role / Timing Role: Pre-regulator stepping down 12V battery to clean 5V rail with Burst Mode® for low-idle power consumption. Use Value: 20μA shutdown IQ and Burst Mode® extend battery life during display sleep; 38V max VIN handles load-dump transients. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar synchronous buck controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3851IMSE#PBF | Same die, 16-lead MSOP package (θJA = 40°C/W), no exposed thermal pad | Lower thermal performance in high-power density layouts; requires larger copper area for heat dissipation | Choose for legacy MSOP footprint compatibility where board space permits larger thermal relief |
| MP2918GL-Z | Monolithic 30V 12A buck converter (integrated MOSFETs); fixed 500kHz frequency; no PLL sync | Eliminates external MOSFET layout complexity but lacks DCR sensing and adjustable frequency | Prefer for cost-sensitive, lower-current (<12A) designs where integration outweighs configurability needs |
Compared with LTC3851IMSE#PBF, the LTC3851IUD#PBF offers superior thermal performance via its exposed-pad QFN, enabling higher continuous current in constrained spaces; versus MP2918GL-Z, it provides greater design flexibility with external MOSFET selection, DCR sensing, and PLL synchronization - critical for high-efficiency, high-reliability systems.
Availability
LTC3851IUD#PBF is available at Aetrix Electronics and suitable for telecom power supplies, industrial FPGA core rails, and distributed DC power systems requiring stable component supply across extended temperature ranges.
Supply support for LTC3851IUD#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 acquired Linear Technology in 2017 and maintains its high-performance analog and power management portfolio. The company specializes in precision signal chain and power solutions for demanding applications.
The LTC3851IUD#PBF belongs to Linear's high-efficiency synchronous controller product line, designed specifically for high-current, wide-input-voltage DC/DC conversion in telecom, industrial, and automotive environments where thermal management and light-load efficiency are critical.
FAQ
What is the maximum input voltage rating for the LTC3851IUD#PBF?
The LTC3851IUD#PBF has an absolute maximum input voltage (VIN) rating of 40V, with recommended continuous operation from 4V to 38V. This wide input range supports unregulated 24V and 48V intermediate bus architectures common in telecom and industrial systems. Exceeding 40V may cause permanent damage per Absolute Maximum Ratings.
How does the ILIM pin configure current limiting on the LTC3851IUD#PBF?
The ILIM pin on the LTC3851IUD#PBF provides tri-level current limit selection: grounding sets max sense threshold to 30mV, floating yields 50mV, and tying to INTVCC selects 75mV. These thresholds directly scale the peak inductor current, enabling precise overcurrent protection tuning without external components - a key feature for robust system-level fault management in the LTC3851IUD#PBF.
Can the LTC3851IUD#PBF synchronize to an external clock, and how is it configured?
Yes, the LTC3851IUD#PBF supports external clock synchronization via its MODE/PLLIN pin. When an external clock (250–750 kHz) is applied, the internal oscillator locks to it in forced continuous conduction mode. A series RC network on FREQ/PLLFLTR serves as the PLL loop filter. This capability enables deterministic EMI reduction and multi-phase interleaving - essential for noise-sensitive applications using the LTC3851IUD#PBF.
What thermal considerations apply to the LTC3851IUD#PBF's QFN package?
The LTC3851IUD#PBF uses a 16-lead 3mm × 3mm QFN with exposed GND pad (Pin 17), requiring soldering to PCB for thermal integrity. Its θJA is 68°C/W and θJC is 4.2°C/W. To maintain operation within the –40°C to 125°C junction limit, designers must provide adequate copper area and thermal vias under the pad - a critical implementation detail for reliable long-term use of the LTC3851IUD#PBF.
Does the LTC3851IUD#PBF support output voltage tracking during startup?
Yes, the LTC3851IUD#PBF supports ratiometric or coincident output voltage tracking via the TK/SS pin. By connecting an external resistor divider from a master supply to TK/SS, the controller ramps its output to match the master's rise profile. This prevents sequencing violations in multi-rail systems - a verified function documented in the LTC3851IUD#PBF datasheet Figure 11 and Applications Information section.
LTC3851IUD#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 ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-QFN (3x3)
LTC3851IUD#PBF FAQ
1.How can I place an order for LTC3851IUD#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3851IUD#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 LTC3851IUD#PBF reliable?
The price and inventory of LTC3851IUD#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3851IUD#PBF is usually 5 days.
3.What payment methods are accepted for LTC3851IUD#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3851IUD#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3851IUD#PBF?
LTC3851IUD#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3851IUD#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 LTC3851IUD#PBF?
For technical support, including LTC3851IUD#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3851IUD#PBF requirements.
6.How does Aetrix verify that LTC3851IUD#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3851IUD#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 LTC3851IUD#PBF meets industry standards.
7.What is the process for return or replacement of LTC3851IUD#PBF?
All LTC3851IUD#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3851IUD#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 LTC3851IUD#PBF part is unused and in its original packaging.
Return procedure for LTC3851IUD#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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