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Analog Devices Inc. LTC3851AIUD#TRPBF
- Part No.:
- LTC3851AIUD#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-WFQFN Exposed Pad
- Datasheet:
-
LTC3851AIUD#TRPBF.pdf
- Description:
- IC REG CTRLR BUCK 16QFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,280
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Product details
Overview
LTC3851AIUD#TRPBF from Analog Devices (formerly Linear Technology) is a high-performance synchronous step-down switching regulator controller driving dual N-channel MOSFETs in a constant-frequency current-mode architecture. It operates from 4V to 38V input, delivers 0.8V–5.5V output with ±1% accuracy, supports phase-lockable 250–750kHz switching, and features OPTI-LOOP® compensation for optimized transient response-used in telecom power supplies requiring tight regulation and fast load-step recovery.
For engineers reviewing the LTC3851AIUD#TRPBF datasheet, LTC3851AIUD#TRPBF pinout, LTC3851AIUD#TRPBF application, or LTC3851AIUD#TRPBF equivalent, key selection criteria include its RSENSE/DCR current sensing flexibility, selectable light-load modes (Burst/Pulse-Skipping/Continuous), 99% duty cycle capability, integrated 5V INTVCC regulator, and thermal performance in the 3mm × 3mm QFN package with exposed pad.
Technical Context
The LTC3851AIUD#TRPBF implements a constant-frequency current-mode control loop where peak inductor current is set by the ITH voltage, and output voltage is regulated via a precision 0.8V reference compared at the FB pin. Its transconductance error amplifier (2 mmho, 3 MHz GBW) drives ITH to maintain regulation across line/load transients.
It integrates a phase-locked loop (PLL) for synchronization to external clocks up to 750 kHz, uses dual gate drivers (TG/BG) with matched 25 ns rise/fall times and 30 ns dead-time control, and includes dedicated protection circuits: output overvoltage lockout (>10%), current foldback limiting, and dropout detection with forced off-time for bootstrap capacitor recharge.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4V to 38V - supports wide industrial and telecom input rails without pre-regulation. |
| Output Voltage Accuracy | ±1% over –40°C to 125°C - ensures stable rail tolerance for sensitive digital loads. |
| Switching Frequency | 250 kHz to 750 kHz (phase-lockable) - balances efficiency vs. magnetics size; PLL enables system-level clock synchronization. |
| Current Sensing | RSENSE or DCR - enables cost-optimized (DCR) or precision (shunt) current limit implementation. |
| Light-Load Modes | Burst Mode®, Pulse-Skipping, Continuous Conduction - selectable via MODE/PLLIN pin for efficiency optimization across load range. |
| Duty Cycle Max | 99% - supports ultra-low dropout operation (e.g., 12V→11.5V conversion) without external LDO. |
| INTVCC Regulator | 5V ±4%, 50 mA - powers internal circuitry and gate drivers; eliminates need for external bias supply. |
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 | 1.22V threshold with 120mV hysteresis; 2µA internal pull-up enables simple RC soft-start or logic control. |
| TK/SS (Pin 2) | Soft-start/tracking input | 1µA internal charge current ramps output voltage; supports ratiometric or coincident tracking of master supplies. |
| ITH (Pin 3) | Error amplifier output / current threshold | Directly sets peak inductor current; used for loop compensation and current foldback programming. |
| VFB (Pin 4) | Feedback input | Compares against 0.8V reference; Kelvin-sense capable for remote voltage regulation. |
| SENSE– (Pin 5) | Current sense inverting input | Connects to low-side of sense resistor or DCR network; enables accurate current measurement. |
| SENSE+ (Pin 6) | Current sense non-inverting input | Connects to high-side of sense resistor or DCR; differential sensing rejects common-mode noise. |
| ILIM (Pin 7) | Current limit select | Tie to GND/FLOAT/INTVCC for 30/50/75 mV max sense threshold - configures overcurrent protection level. |
| GND (Pin 8 + Exposed Pad) | Signal and power ground | Exposure pad must be soldered to PCB ground plane for thermal management and low-noise reference. |
| 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 | Decoupled with ≥2.2µF ceramic/tantalum; powers control logic and gate drivers. |
| VIN (Pin 11) | Main input supply | Accepts 4V–38V; requires local bulk capacitance to handle high di/dt during switching. |
| BOOST (Pin 12) | Floating bootstrap supply | Charged via external diode/capacitor; enables high-side N-MOSFET drive above VIN. |
| TG (Pin 13) | Top gate driver output | Floating driver 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 high-side MOSFET source; experiences full VIN-to-GND swing. |
| MODE/PLLIN (Pin 15) | Mode selection / sync input | Selects Burst/Pulse-Skipping/Continuous mode or accepts external clock (250–750 kHz) for PLL sync. |
| FREQ/PLLFLTR (Pin 16) | Oscillator frequency / PLL filter | Resistor-to-GND sets nominal frequency; RC network filters PLL feedback for stable synchronization. |
Key Features
| Feature | Design Value |
|---|---|
| OPTI-LOOP® Compensation | Minimizes required output capacitance by enabling stable loop response across wide ESR/capacitance variations - reduces BOM count and board area. |
| Tri-Level ILIM Programming | 30/50/75 mV current sense thresholds via single pin - simplifies overcurrent protection tuning without resistor changes. |
| 99% Maximum Duty Cycle | Enables near-dropout operation (e.g., 12V→11.8V) - eliminates need for post-regulation in high-VIN systems. |
| Integrated 5V INTVCC Regulator | Supplies 50 mA at 5V ±4% - removes external bias supply, reducing component count and layout complexity. |
| Output Overvoltage Protection | Locks out top MOSFET and activates bottom MOSFET on >10% VOUT overshoot - prevents damage to downstream ICs during transients. |
Applications
| Telecom Power Supply | Industrial DC-DC Converter |
|---|---|
Use Scenario: Intermediate bus converter in 48V telecom shelf powering 12V/5V/3.3V point-of-load rails. IC Role / Device Role / Timing Role: Primary synchronous buck controller regulating 48V input to 12V intermediate bus with tight line/load regulation. Use Value: ±1% output accuracy and 250–750kHz programmability enable compliance with GR-1253-CORE transient requirements and compact magnetics design. | Use Scenario: Field-programmable gate array (FPGA) core voltage supply in programmable logic controller (PLC) backplane. IC Role / Device Role / Timing Role: High-efficiency step-down controller delivering 1.2V @ 15A with fast transient response to FPGA dynamic load steps. Use Value: OPTI-LOOP® compensation and 99% duty cycle support stable 1.2V rail under 10A/µs load transients without excessive output capacitance. |
| Automotive Infotainment System | Distributed Data Center PSU |
Use Scenario: Powering ADAS camera module processor and image sensor from 12V battery rail with strict EMI limits. IC Role / Device Role / Timing Role: Synchronous buck controller operating in Burst Mode® at light loads to meet CISPR-25 Class 5 conducted emissions. Use Value: Selectable light-load modes reduce switching noise during idle periods while maintaining <100 µA shutdown IQ for battery longevity. | Use Scenario: Redundant 12V intermediate bus converter in modular server power architecture with hot-swap capability. IC Role / Device Role / Timing Role: Controller with phase-lockable oscillator synchronized to system clock for ripple cancellation across parallel modules. Use Value: PLL synchronization enables interleaved operation of multiple LTC3851AIUD#TRPBF units, cutting input/output ripple by up to 50% versus free-running units. |
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#TRPBF | Same die, 16-lead MSOP package (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 is unavailable. |
| MP2315DJ-LF-Z | Integrated power stage (40V, 3A), fixed 500kHz, no PLL sync or tri-level ILIM. | Targeted at space-constrained, medium-current applications without need for external MOSFETs or system-level clock sync. | Choose for simplified BOM and layout where 3A output and fixed frequency suffice. |
Compared with LTC3851EMSE#TRPBF, the LTC3851AIUD#TRPBF offers superior thermal performance in high-current designs due to its QFN's lower θJA and exposed pad; versus MP2315DJ-LF-Z, it provides higher current scalability, flexible frequency control, and advanced protection features at the cost of external FETs.
Availability
LTC3851AIUD#TRPBF is available at Aetrix Electronics and suitable for telecom power supplies, industrial DC-DC converters, and automotive infotainment systems requiring stable component supply, long-term lifecycle support, and traceable sourcing.
Supply support for LTC3851AIUD#TRPBF 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 semiconductor leader specializing in high-performance analog, mixed-signal, and power management ICs for precision, reliability, and efficiency-critical applications.
The LTC3851A product line delivers high-efficiency, high-voltage synchronous buck controllers targeting demanding power systems in telecom, industrial, and automotive markets where wide input range, precise regulation, and robust protection are essential.
FAQ
What is the maximum input voltage rating for the LTC3851AIUD#TRPBF?
The LTC3851AIUD#TRPBF 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 industrial or telecom systems. Exceeding 40V risks permanent damage per Absolute Maximum Ratings. The device includes undervoltage lockout on INTVCC (3.25V threshold) to prevent erratic operation during brownout conditions.
How does the ILIM pin configure current limit thresholds on the LTC3851AIUD#TRPBF?
The ILIM pin on the LTC3851AIUD#TRPBF selects one of three maximum current sense thresholds: 30 mV (ILIM = GND), 50 mV (ILIM = FLOAT), or 75 mV (ILIM = INTVCC). This tri-level configuration directly sets the peak inductor current trip point for overcurrent protection and foldback limiting, eliminating the need for external resistors and enabling rapid design iteration across different current levels without changing the sense resistor.
Can the LTC3851AIUD#TRPBF synchronize to an external clock, and what are the requirements?
Yes, the LTC3851AIUD#TRPBF can synchronize its internal oscillator to an external clock applied to the MODE/PLLIN pin. The external clock must be 250–750 kHz, and a series RC network must be connected between FREQ/PLLFLTR and GND to serve as the PLL loop filter. The controller enters forced continuous conduction mode during synchronization, ensuring deterministic timing for multi-phase or noise-sensitive applications.
What is the purpose of the TK/SS pin on the LTC3851AIUD#TRPBF, and how is it used for soft-start?
The TK/SS pin on the LTC3851AIUD#TRPBF controls output voltage ramp rate during startup. An internal 1 µA current charges an external capacitor connected from TK/SS to GND, generating a linear voltage ramp. As TK/SS rises from 0V to 0.8V, the regulated output voltage follows proportionally-enabling controlled soft-start or ratiometric tracking of another supply. During shutdown, the pin is actively pulled low to reset the sequence.
Does the LTC3851AIUD#TRPBF support both RSENSE and DCR current sensing, and how is the selection made?
Yes, the LTC3851AIUD#TRPBF supports both RSENSE (shunt resistor) and DCR (inductor winding resistance) current sensing. No pin configuration or register setting is required-the topology is selected by external circuit connection: SENSE+ and SENSE– connect across the shunt for RSENSE, or across the DCR network (RC filter) for DCR sensing. DCR reduces power loss and cost in high-current designs; RSENSE provides higher accuracy and better temperature stability.
LTC3851AIUD#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-WFQFN Exposed Pad
- Packaging:
- Tape & Reel (TR)
- 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:
- 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)
LTC3851AIUD#TRPBF FAQ
1.How can I place an order for LTC3851AIUD#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3851AIUD#TRPBF 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 LTC3851AIUD#TRPBF reliable?
The price and inventory of LTC3851AIUD#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3851AIUD#TRPBF is usually 5 days.
3.What payment methods are accepted for LTC3851AIUD#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3851AIUD#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3851AIUD#TRPBF?
LTC3851AIUD#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3851AIUD#TRPBF 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 LTC3851AIUD#TRPBF?
For technical support, including LTC3851AIUD#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3851AIUD#TRPBF requirements.
6.How does Aetrix verify that LTC3851AIUD#TRPBF is sourced from the original manufacturer or authorized distributors?
All LTC3851AIUD#TRPBF 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 LTC3851AIUD#TRPBF meets industry standards.
7.What is the process for return or replacement of LTC3851AIUD#TRPBF?
All LTC3851AIUD#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3851AIUD#TRPBF, 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 LTC3851AIUD#TRPBF part is unused and in its original packaging.
Return procedure for LTC3851AIUD#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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