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Analog Devices Inc. LTC3851EMSE#PBF
- Part No.:
- LTC3851EMSE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 16-TFSOP (0.118", 3.00mm Width) Exposed Pad
- Datasheet:
-
LTC3851EMSE#PBF.pdf
- Description:
- IC REG CTRLR BUCK 16MSOP
- Quantity:
- Payment:
- Shipping:
Inventory:3,686
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Product details
Overview
LTC3851EMSE#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 adjustable output with ±1% accuracy, operates up to 750kHz, and features OPTI-LOOP® compensation, selectable light-load modes (Burst/Pulse-Skip/CCM), and integrated 5V INTVCC regulator - used in telecom power supplies requiring tight regulation and thermal efficiency.
For engineers reviewing the LTC3851EMSE#PBF datasheet, LTC3851EMSE#PBF pinout, LTC3851EMSE#PBF application, or LTC3851EMSE#PBF equivalent, key selection criteria include its RSENSE/DCR current sensing flexibility, phase-lockable oscillator, 99% duty cycle capability, soft-start/tracking via TK/SS pin, and thermally enhanced 16-lead MSOP package with exposed pad for industrial DC-DC converter design.
Technical Context
The LTC3851EMSE#PBF implements a constant-frequency current-mode control architecture with slope compensation, where peak inductor current is set by the ITH voltage and compared against sensed voltage at SENSE+/SENSE–. Its transconductance error amplifier (gm = 2 mmho, GBW = 3 MHz) drives ITH to regulate VFB to 0.8V reference with ±1% accuracy over temperature and line/load.
It integrates dual gate drivers (TG/BG) with matched 25ns rise/fall times, anti-shoot-through logic, and programmable current limit via ILIM pin (30/50/75 mV thresholds). The MODE/PLLIN pin enables synchronization to external clocks (250–750 kHz), while FREQ/PLLFLTR sets internal oscillator frequency or serves as PLL loop filter node.
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 under varying load/temperature. |
| Switching Frequency | 250kHz to 750kHz - adjustable via resistor on FREQ/PLLFLTR or synchronizable externally for EMI control. |
| Current Sense Threshold | 30/50/75 mV (ILIM-selectable) - enables accurate, low-loss current limiting with RSENSE or DCR sensing. |
| INTVCC Regulator | 5.0V ±2%, 50mA max - powers internal circuitry and gate drivers; eliminates need for external bias supply. |
| Light-Load Operation | Burst Mode®, Pulse-Skipping, or Forced CCM - selectable via MODE/PLLIN for optimized efficiency vs. ripple/noise trade-off. |
| Duty Cycle Capability | Up to 99% - supports ultra-low dropout operation during VIN-to-VOUT transitions (e.g., 5V→3.3V). |
Pinout & Package
Package: 16-lead plastic MSOP (MSE) with exposed thermal pad (Pin 17 = GND), θJA = 40°C/W, rated for –40°C to +85°C operation.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| MODE/PLLIN (Pin 1) | Mode selection & sync input | Selects Burst/Pulse-Skip/CCM or accepts external clock (250–750 kHz) to force synchronization and eliminate beat frequencies. |
| FREQ/PLLFLTR (Pin 2) | Oscillator programming / PLL filter | Connects to GND via resistor to set nominal frequency; serves as PLL low-pass filter node when synchronized. |
| RUN (Pin 3) | Enable control | Logic-high (>1.25V) enables IC; internal 2μA pull-up allows simple RC delay start-up; <1.1V forces shutdown with <20μA IQ. |
| TK/SS (Pin 4) | Soft-start & tracking input | Internal 1μA current charges external capacitor for linear VOUT ramp; also accepts master supply divider for ratiometric tracking. |
| ITH (Pin 5) | Error amplifier output & current threshold | Voltage sets peak inductor current; also serves as compensation node for OPTI-LOOP® stability across wide COUT/ESR range. |
| VFB (Pin 6) | Feedback input | Compares remote-sensed output voltage against 0.8V reference; ±1% accuracy ensures tight regulation. |
| SENSE– (Pin 7) | Current sense inverting input | High-impedance (±1μA bias) node tied to low-side of sense resistor or DCR network; common-mode range 0–5.5V. |
| SENSE+ (Pin 8) | Current sense non-inverting input | Paired with SENSE– for differential current sensing; enables accurate DCR or RSENSE-based current limit programming. |
| ILIM (Pin 9) | Current limit range select | Tie to GND/FLOAT/INTVCC to set max sense threshold to 30/50/75 mV - adjusts current limit without changing RSENSE. |
| GND (Pin 10) | Analog ground reference | Kelvin connection point for all small-signal components; exposed pad must be soldered for thermal and noise performance. |
| BG (Pin 11) | Bottom gate driver output | Drives low-side N-MOSFET gate between GND and INTVCC; 1.1Ω pull-down ensures fast turn-off and prevents shoot-through. |
| INTVCC (Pin 12) | Internal 5V regulator output | Supplies internal circuitry and gate drivers; requires ≥2.2μF low-ESR ceramic/tantalum decoupling to GND. |
| VIN (Pin 13) | Main input supply | Accepts 4–38V input; powers INTVCC LDO and provides energy to boost capacitor via BOOST pin. |
| BOOST (Pin 14) | Floating bootstrap supply | Connects to (+) terminal of bootstrap capacitor; swings from ~VIN+5V down to ~INTVCC–0.7V for top gate drive. |
| TG (Pin 15) | Top gate driver output | Floating driver output referenced to SW node; swing = INTVCC, enabling high-side N-MOSFET drive without P-channel. |
| SW (Pin 16) | Switch node | Connects to inductor and MOSFET sources; voltage swings from ~–0.4V (Schottky drop) to VIN - critical for layout and EMI. |
Key Features
| Feature | Design Value |
|---|---|
| OPTI-LOOP® Compensation | Minimizes required output capacitance and simplifies loop stability across diverse COUT types (ceramic, polymer, electrolytic) and ESR values. |
| Tri-Level Current Limit (ILIM) | Enables precise, resistor-free current limit adjustment (30/50/75 mV) to match MOSFET RDS(on) or sense resistor value without redesign. |
| 99% Maximum Duty Cycle | Supports near-dropout operation (e.g., 5V→4.95V), extending usable input range and improving efficiency in high-VIN, low-VOUT applications. |
| Programmable Light-Load Modes | Reduces quiescent current to 20μA in shutdown and enables system-level efficiency optimization via Burst Mode® (high-efficiency) or CCM (low-noise). |
| Integrated 5V INTVCC Regulator | Eliminates need for external bias rail; delivers up to 50mA to power gate drivers and internal logic - reduces BOM count and board space. |
Applications
| Telecom Power Supply | Industrial DC-DC Converter |
|---|---|
|
Use Scenario: 48V intermediate bus conversion to 3.3V/5V for base station RF modules and packet processing units. IC Role / Device Role / Timing Role: Primary synchronous buck controller managing high-current, high-efficiency power delivery with strict transient response requirements. Use Value: OPTI-LOOP® compensation maintains stability with mixed-output-capacitor banks; 750kHz operation enables compact magnetics for dense PCB layouts. |
Use Scenario: DIN-rail mounted 24V-to-12V/5V conversion in PLC I/O modules and motor drive auxiliary supplies. IC Role / Device Role / Timing Role: Robust step-down controller handling wide input transients (e.g., 18–36V) and delivering regulated outputs with ±1% accuracy. Use Value: RSENSE/DCR sensing flexibility accommodates cost-sensitive or high-efficiency designs; 99% duty cycle supports brownout operation. |
| Automotive Infotainment System | Distributed Data Center PSU |
|
Use Scenario: 12V battery-derived 5V/3.3V rails for head unit processors, display drivers, and audio codecs in harsh-temperature environments. IC Role / Device Role / Timing Role: High-reliability buck controller with thermal-enhanced MSOP package and –40°C to +85°C rating for under-hood proximity. Use Value: Burst Mode® operation achieves >85% efficiency at 10mA load, extending standby time; TK/SS pin enables safe power sequencing with MCU. |
Use Scenario: Point-of-load (POL) conversion from 12V intermediate bus to 1.8V/1.2V for FPGA and ASIC cores in server rack power systems. IC Role / Device Role / Timing Role: Precision current-mode controller supporting multi-phase synchronization via MODE/PLLIN for ripple cancellation. Use Value: Phase-lockable 750kHz operation minimizes magnetic size while enabling deterministic timing for coordinated multi-rail startup. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar synchronous buck controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8640S | Monolithic 4A buck (integrated MOSFETs); 3V–42V input; 200kHz–3MHz sync range; no ILIM tri-level or DCR sensing support. | Better for space-constrained designs needing full integration; unsuitable for >10A or discrete MOSFET optimization. | Choose LT8640S if board area and BOM count are prioritized over discrete FET selection and DCR sensing flexibility. |
| MP2918 | Controller with PMBus interface; 4.5V–60V input; 0.6V reference; supports VR13/IMVP8 protocols; no OPTI-LOOP® or Burst Mode®. | Targeted at CPU/GPU VRMs with digital telemetry; lacks analog light-load optimization for general-purpose converters. | Choose MP2918 only when digital monitoring, adaptive voltage positioning, or dynamic VID control are required. |
Compared with LT8640S and MP2918, the LTC3851EMSE#PBF offers unmatched analog control precision, tri-level current limit, and OPTI-LOOP® stability tuning - making it ideal for high-reliability, thermally demanding, or custom discrete-FET power stages where monolithic or digital alternatives compromise on flexibility or efficiency at light loads.
Availability
LTC3851EMSE#PBF 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 guaranteed –40°C to +85°C operation.
Supply support for LTC3851EMSE#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, serving industrial, automotive, communications, and healthcare markets.
The LTC3851EMSE#PBF belongs to Linear's high-efficiency synchronous controller product line, designed specifically for high-current, wide-input-voltage DC-DC conversion in space- and thermal-constrained applications where discrete MOSFET optimization and analog control fidelity are critical.
FAQ
What is the maximum switching frequency supported by the LTC3851EMSE#PBF?
The LTC3851EMSE#PBF supports a phase-lockable fixed-frequency range of 250kHz to 750kHz. At RFREQ = 36kΩ, the typical frequency is 750kHz. This upper limit enables compact magnetics and reduced output ripple while maintaining high efficiency - critical for high-density telecom and industrial power supplies where the LTC3851EMSE#PBF is commonly deployed.
How does the ILIM pin affect current limiting in the LTC3851EMSE#PBF?
The ILIM pin on the LTC3851EMSE#PBF selects one of three maximum current sense thresholds: 30mV (ILIM = GND), 50mV (ILIM = FLOAT), or 75mV (ILIM = INTVCC). This tri-level configuration allows precise adaptation of the current limit to match RSENSE value or inductor DCR without changing external components - a key advantage of the LTC3851EMSE#PBF in scalable power designs.
Can the LTC3851EMSE#PBF operate with an input voltage below 4V?
No - the absolute minimum operating input voltage for the LTC3851EMSE#PBF is 4V, as specified in the Electrical Characteristics table. Below this, the INTVCC regulator cannot maintain 5V output, causing functional failure. The device also has a 3.25V undervoltage lockout on INTVCC, ensuring reliable startup only within the 4V–38V valid range defined for the LTC3851EMSE#PBF.
What is the purpose of the exposed thermal pad (Pin 17) on the LTC3851EMSE#PBF MSOP package?
The exposed thermal pad (Pin 17) on the LTC3851EMSE#PBF is electrically and thermally connected to GND. It must be soldered to a PCB copper pour to achieve the specified θJA = 40°C/W and prevent thermal shutdown under sustained load. Failure to connect this pad degrades thermal performance and risks reliability issues - a mandatory layout requirement for the LTC3851EMSE#PBF in production designs.
Does the LTC3851EMSE#PBF support output voltage tracking during startup?
Yes - the LTC3851EMSE#PBF supports ratiometric output voltage tracking via the TK/SS pin. By connecting an external resistor divider from a master supply to TK/SS, the LTC3851EMSE#PBF regulates VOUT to follow the master rail's ramp profile. This enables safe power sequencing in multi-rail systems, such as FPGA or processor core/logic supply coordination, without requiring additional supervisory ICs.
LTC3851EMSE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-TFSOP (0.118", 3.00mm Width) 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-MSOP-EP
LTC3851EMSE#PBF FAQ
1.How can I place an order for LTC3851EMSE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3851EMSE#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 LTC3851EMSE#PBF reliable?
The price and inventory of LTC3851EMSE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3851EMSE#PBF is usually 5 days.
3.What payment methods are accepted for LTC3851EMSE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3851EMSE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3851EMSE#PBF?
LTC3851EMSE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3851EMSE#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 LTC3851EMSE#PBF?
For technical support, including LTC3851EMSE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3851EMSE#PBF requirements.
6.How does Aetrix verify that LTC3851EMSE#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3851EMSE#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 LTC3851EMSE#PBF meets industry standards.
7.What is the process for return or replacement of LTC3851EMSE#PBF?
All LTC3851EMSE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3851EMSE#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 LTC3851EMSE#PBF part is unused and in its original packaging.
Return procedure for LTC3851EMSE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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