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Analog Devices Inc. LTC3851AEUD-1#PBF
- Part No.:
- LTC3851AEUD-1#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LTC3851AEUD-1#PBF.pdf
- Description:
- IC REG CTRLR BUCK 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:144
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Product details
Overview
LTC3851AEUD-1#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, features phase-lockable 250kHz–750kHz switching, and integrates PGOOD monitoring and OPTI-LOOP® compensation for wide output capacitor/ESR optimization.
For engineers reviewing the LTC3851AEUD-1#PBF datasheet, LTC3851AEUD-1#PBF pinout, LTC3851AEUD-1#PBF application, or LTC3851AEUD-1#PBF equivalent, key selection criteria include its 16-pin 3mm × 3mm QFN package, RSENSE/DCR current sensing flexibility, selectable light-load modes (Burst/Pulse-Skip/Continuous), and automotive-grade –40°C to 125°C operation with integrated overvoltage protection and 99% duty cycle capability.
Technical Context
The LTC3851AEUD-1#PBF implements a constant-frequency current-mode control architecture with an internal transconductance error amplifier (gm = 2 mmho, GBW = 3 MHz) and precision 0.8V reference (±1% over temperature). Its OPTI-LOOP® compensation minimizes required output capacitance by adapting loop response to COUT and ESR variations.
It features dual gate drivers (TG/BG) with matched 25ns rise/fall times, 30ns dead-time control, and integrated dropout detection enabling 99% duty cycle operation. The MODE/PLLIN pin provides three light-load operating modes and external clock synchronization up to 750kHz, while FREQ/PLLFLTR sets nominal frequency via resistor (250–750kHz range).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 38V - supports 12V/24V/36V battery and intermediate bus systems without pre-regulation. |
| Output Voltage Accuracy | ±1% at 0.8V reference - ensures tight regulation across load, line, and temperature for sensitive digital loads. |
| Switching Frequency | 250kHz to 750kHz, phase-lockable - enables EMI control and optimal trade-off between efficiency and magnetics size. |
| Light-Load Operation | Burst Mode®, Pulse-Skipping, or Continuous Conduction - selectable via MODE/PLLIN for efficiency vs. ripple/noise optimization. |
| Current Sensing | RSENSE or DCR - flexible implementation supporting cost-sensitive (DCR) or precision (shunt) designs. |
| Power Good Output | Open-drain PGOOD with ±10% window and 17µs mask - provides reliable system power sequencing and fault indication. |
| Shutdown Current | 20µA - enables ultra-low quiescent power in standby or battery-backed systems. |
Pinout & Package
Package: 16-lead (3mm × 3mm) plastic QFN with exposed thermal pad (Pin 17 = GND), rated for –40°C to 125°C junction temperature (θJA = 68°C/W).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| RUN (Pin 1) | Enable control input | Active-high logic input with 1.22V threshold and 2μA internal pull-up; pulls low to disable IC and INTVCC regulator. |
| TK/SS (Pin 2) | Soft-start/tracking control | 1μA internal current source charges external capacitor to ramp VOUT linearly; supports ratiometric or coincident tracking of master supply. |
| ITH (Pin 3) | Error amplifier output / current limit setpoint | Controls peak inductor current; voltage directly scales current sense threshold (e.g., 1.2V → 53mV max at H-grade). |
| VFB (Pin 4) | Feedback input | Compares resistive divider output against 0.8V reference; ±10% window triggers PGOOD assertion. |
| SENSE– (Pin 5) | Current sense inverting input | Connects to low-side of sense resistor or DCR network; referenced to SW node for accurate differential sensing. |
| SENSE+ (Pin 6) | Current sense non-inverting input | Connects to high-side of sense resistor or DCR network; enables accurate current measurement independent of ground path. |
| PGOOD (Pin 7) | Power good indicator | Open-drain output pulled low when VFB is outside ±10% of 0.8V, during soft-start, or RUN = low. |
| GND (Pins 8 & 17) | Signal and thermal ground | Pins 8 (signal) and 17 (exposed pad) must be Kelvin-connected to minimize noise and maximize thermal dissipation. |
| BG (Pin 9) | Bottom gate driver output | Drives gate of low-side N-MOSFET between GND and INTVCC; 1.1Ω pull-down resistance ensures fast turn-off. |
| INTVCC (Pin 10) | Internal 5V regulator output | Supplies control circuitry; requires ≥2.2µF low-ESR ceramic/tantalum decoupling to GND for stability. |
| VIN (Pin 11) | Main input supply | Accepts 4V–38V input; powers INTVCC LDO and provides energy to boost capacitor during high-duty-cycle operation. |
| BOOST (Pin 12) | Floating bootstrap supply | Swings from ~VIN + INTVCC down to ~INTVCC − 0.4V; charges external bootstrap capacitor to drive TG. |
| TG (Pin 13) | Top gate driver output | Floating driver with INTVCC swing referenced to SW node; 2.2Ω pull-up ensures robust high-side MOSFET turn-on. |
| SW (Pin 14) | Switch node connection | Connects to inductor and external Schottky diode cathode; voltage swings from ~–0.4V to VIN. |
| MODE/PLLIN (Pin 15) | Mode selection / PLL sync input | Selects Burst Mode (50–250kΩ to INTVCC), Pulse-Skip (GND), or Continuous (tied to INTVCC); accepts external clock up to 750kHz. |
| FREQ/PLLFLTR (Pin 16) | Oscillator programming / PLL filter | Resistor-to-GND sets nominal frequency (250–750kHz); RC network serves as PLL loop filter when synchronized. |
Key Features
| Feature | Design Value |
|---|---|
| OPTI-LOOP® Compensation | Adapts loop gain/phase margin to actual output capacitor ESR and value-reduces need for large bulk capacitance and simplifies stability tuning. |
| 99% Maximum Duty Cycle | Enables ultra-low dropout operation (e.g., 5V→4.95V at 38V input), critical for high-input-voltage, low-VOUT applications like point-of-load conversion. |
| Integrated Overvoltage Protection | Hardware-based OV comparator disables TG and enables BG if VFB exceeds +10% of 0.8V-prevents damage to downstream loads during transients. |
| Current Foldback Limiting | Reduces peak MOSFET current under short-circuit conditions by lowering ITH threshold-limits thermal stress without external circuitry. |
| Thermally Enhanced QFN | 3mm × 3mm package with exposed GND pad achieves θJC = 4.2°C/W-enables >15A continuous output with proper PCB copper area. |
Applications
| Telecom Intermediate Bus Converter | Automotive ADAS Power Supply |
|---|---|
|
Use Scenario: Converting 24V vehicle battery to stable 3.3V/5V for radar processors and camera modules. IC Role / Device Role / Timing Role: Primary synchronous buck controller managing high-efficiency, low-noise power delivery with strict transient response requirements. Use Value: 99% duty cycle enables operation during cold-crank (down to 4.5V), while Burst Mode reduces quiescent current to <20µA in sleep states. |
Use Scenario: Regulating 12V battery rail to 1.2V/1.8V for SoCs in autonomous driving ECUs. IC Role / Device Role / Timing Role: High-accuracy, current-mode controller delivering ±1% output regulation with fast load-step response (<100µs). Use Value: OPTI-LOOP® compensation maintains stability across wide temperature range (–40°C to 125°C) and varying ceramic capacitor aging. |
| Industrial PLC I/O Module | Distributed DC Power System |
|
Use Scenario: Generating isolated 5V/12V rails from 24V/48V backplane in programmable logic controllers. IC Role / Device Role / Timing Role: Non-isolated buck controller providing primary regulated bus for downstream isolated DC/DC converters. Use Value: RSENSE/DCR flexibility allows cost-optimized design; PGOOD signal coordinates startup sequencing with FPGA and analog front-ends. |
Use Scenario: Point-of-load regulation in server rack power architectures with 48V intermediate distribution. IC Role / Device Role / Timing Role: High-frequency (750kHz) synchronous controller minimizing inductor size while maintaining >90% efficiency at 10A. Use Value: Phase-lockable oscillator synchronizes multiple LTC3851AEUD-1#PBF units to suppress beat frequencies and simplify EMI filtering. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar synchronous step-down controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8640S | Monolithic 42V input, 6A buck regulator (integrated MOSFETs); no external power stage required. | Lower BOM count and layout complexity, but fixed 6A current limit and less flexible current sensing (no DCR option). | Choose LT8640S for compact, lower-risk designs where 6A output suffices and integrated FETs meet thermal requirements. |
| LTC3891 | 40V input, dual-output synchronous controller with independent mode control per channel; higher IQ (45µA shutdown). | Supports two independent regulated outputs (e.g., 5V + 3.3V) from single controller; lacks PGOOD on secondary channel. | Choose LTC3891 when dual-output coordination, independent light-load mode selection, or higher input voltage margin (>38V) is required. |
Compared with LT8640S and LTC3891, the LTC3851AEUD-1#PBF offers superior flexibility in external MOSFET selection, DCR sensing support, and precise 0.8V reference accuracy-making it ideal for high-current, thermally constrained, or multi-rail industrial applications where discrete power stage optimization is critical.
Availability
LTC3851AEUD-1#PBF is available at Aetrix Electronics and suitable for telecom intermediate bus converters, automotive ADAS power supplies, and industrial PLC I/O modules requiring stable component supply with full lifecycle support.
Supply support for LTC3851AEUD-1#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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors.
The LTC3851A family was designed specifically for high-efficiency, high-current synchronous buck conversion in demanding industrial, automotive, and telecom environments-emphasizing precision regulation, thermal robustness, and flexible current sensing.
FAQ
What is the maximum input voltage rating for the LTC3851AEUD-1#PBF?
The LTC3851AEUD-1#PBF has an absolute maximum input voltage (VIN) rating of 40V. Its operational input range is specified from 4V to 38V, making it suitable for 24V and 36V battery systems and intermediate bus applications. Exceeding 40V may cause permanent damage per Absolute Maximum Ratings.
Does the LTC3851AEUD-1#PBF support DCR current sensing?
Yes, the LTC3851AEUD-1#PBF explicitly supports both RSENSE shunt resistor and DCR (inductor resistance) current sensing via dedicated SENSE+ and SENSE– pins. DCR sensing eliminates power loss and cost of external resistors-particularly advantageous in high-current designs where efficiency and thermal management are critical.
How does the PGOOD function behave during startup of the LTC3851AEUD-1#PBF?
The PGOOD pin on the LTC3851AEUD-1#PBF remains low during soft-start (while TK/SS voltage ramps), until VFB stabilizes within ±10% of 0.8V for longer than the internal 17µs power-bad mask timer. Once valid regulation is confirmed, PGOOD goes high (open-drain, requires external pull-up), signaling system readiness for downstream sequencing.
Can the LTC3851AEUD-1#PBF synchronize to an external clock?
Yes, the LTC3851AEUD-1#PBF can synchronize its internal oscillator to an external clock applied to the MODE/PLLIN pin. When driven by a clean square wave (250–750kHz), the device enters forced continuous conduction mode and locks phase-enabling deterministic switching and reduced EMI in multi-converter systems.
What thermal considerations apply to the LTC3851AEUD-1#PBF in its 3mm × 3mm QFN package?
The LTC3851AEUD-1#PBF in the UD package has θJA = 68°C/W and θJC = 4.2°C/W. Effective thermal design requires soldering the exposed pad (Pin 17) to a minimum 200mm² copper pour with ≥4 thermal vias to inner ground planes. Junction temperature must remain ≤125°C under worst-case load and ambient conditions.
LTC3851AEUD-1#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:
- 235kHz ~ 750kHz
- Duty Cycle (Max):
- 99%
- Synchronous Rectifier:
- Yes
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Enable, Frequency Control, Power Good, Soft Start, Tracking
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-QFN (3x3)
LTC3851AEUD-1#PBF FAQ
1.How can I place an order for LTC3851AEUD-1#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3851AEUD-1#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 LTC3851AEUD-1#PBF reliable?
The price and inventory of LTC3851AEUD-1#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3851AEUD-1#PBF is usually 5 days.
3.What payment methods are accepted for LTC3851AEUD-1#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3851AEUD-1#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3851AEUD-1#PBF?
LTC3851AEUD-1#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3851AEUD-1#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 LTC3851AEUD-1#PBF?
For technical support, including LTC3851AEUD-1#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3851AEUD-1#PBF requirements.
6.How does Aetrix verify that LTC3851AEUD-1#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3851AEUD-1#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 LTC3851AEUD-1#PBF meets industry standards.
7.What is the process for return or replacement of LTC3851AEUD-1#PBF?
All LTC3851AEUD-1#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3851AEUD-1#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 LTC3851AEUD-1#PBF part is unused and in its original packaging.
Return procedure for LTC3851AEUD-1#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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