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Analog Devices Inc. LTC3856EFE#PBF
- Part No.:
- LTC3856EFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 38-TFSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LTC3856EFE#PBF.pdf
- Description:
- IC REG CTRLR BUCK 38TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:140
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Product details
Overview
LTC3856EFE#PBF from Analog Devices (formerly Linear Technology) is a dual-channel, 2-phase synchronous step-down DC/DC controller driving all-N-channel MOSFET stages for high-current POL applications. It features ±0.75% reference accuracy, 4.5V–38V input range, 0.6V–5V output range, differential remote sensing, and supports up to 12-phase stacking. Used in telecom power supplies delivering 1.5V/50A with <36mV load transient overshoot.
For engineers reviewing the LTC3856EFE#PBF datasheet, LTC3856EFE#PBF pinout, LTC3856EFE#PBF application, or LTC3856EFE#PBF equivalent, key selection criteria include phase-lockable 250–770kHz operation, DCR temperature compensation, active voltage positioning (AVP), and dual independent current-sense inputs with programmable thresholds across three ILIM settings.
Technical Context
The LTC3856EFE#PBF implements a constant-frequency current-mode control architecture with two independent PWM channels operating out-of-phase to reduce input/output ripple and EMI. Each channel integrates high-speed gate drivers (TG/BG RDS(ON) ≤ 2.6Ω/1.1Ω), a dedicated current-sense comparator with selectable threshold (25–84mV), and DCR sensing with temperature-compensated bias current (9–11µA).
It embeds a true remote-sense differential amplifier (gain = 0.997–1.003 V/V, PSRR = 100dB) referenced to DIFFP/DIFFN, enabling precise load-point regulation. Phase synchronization is achieved via PLLIN or CLKOUT sharing, supporting scalable multi-phase designs up to 12 phases with programmable phase offsets (60°/90°/120°).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4.5V to 38V - supports 5V, 12V, 24V, and 28V intermediate bus systems without external regulators. |
| Output Voltage Range | 0.6V to 5.0V - covers core voltages for FPGAs, ASICs, and microprocessors; extends to 3.3V when using differential amplifier. |
| Reference Accuracy | ±0.75% at 0.6V - ensures tight output regulation under line/load/temperature variation for high-precision POL rails. |
| Switching Frequency | 250kHz to 770kHz - adjustable via FREQ pin; enables optimization of size vs. efficiency; phase-lockable for noise-sensitive systems. |
| Current Sense Method | RSENSE or DCR - eliminates sense resistor losses; DCR tempco compensation maintains accuracy over –40°C to 125°C. |
| Efficiency Peak | Up to 95% - achieved at 1.5V/50A with optimized layout and low-RDS(ON) MOSFETs; Burst Mode extends light-load efficiency. |
| Thermal Range | –40°C to 125°C junction - qualified for industrial and telecom environments; TSSOP package θJA = 25°C/W. |
Pinout & Package
Package: 38-lead plastic TSSOP (FE package), exposed pad (Pin 39) soldered to SGND/PGND for thermal and electrical performance. Pin pitch: 0.5mm.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| FREQ (Pin 1) | Oscillator frequency programming | Resistor-to-ground sets fSW from 250–770kHz; DC voltage override enables dynamic frequency scaling. |
| RUN (Pin 2) | Enable/disable control | 1.22V threshold with 80mV hysteresis; internal 1µA pull-up enables simple RC soft-start sequencing. |
| SENSE1+, SENSE2+ (Pins 3,13) | Current sense comparator (+) input | Connects to DCR network or sense resistor; ±1µA bias current minimizes error in precision sensing. |
| SENSE1–, SENSE2– (Pins 4,14) | Current sense comparator (–) input | References to SW node or output rail; enables accurate inductor current measurement in high-side configuration. |
| TK/SS (Pin 6) | Soft-start/tracking control | 1.25µA internal current charges external capacitor for linear VOUT ramp; supports supply tracking via resistor divider. |
| VFB (Pin 7) | Error amplifier feedback input | Receives regulated voltage from DIFFOUT/resistive divider; ±50nA input current preserves loop stability. |
| ITH (Pin 8) | Error amplifier output / current threshold | Directly programs peak inductor current per phase; transconductance = 2.0 mmho enables stable compensation. |
| SGND (Pin 9) | Signal and power ground reference | Single-point connection point for compensation components and small-signal circuitry; tied to PGND at one location. |
| AVP (Pin 10) | Active voltage positioning slope | Resistor to DIFFP sets load-line droop (e.g., 2.5V max VOUT); requires differential amplifier use for AVP functionality. |
| ITEMP (Pin 11) | DCR temperature compensation input | Connects to NTC thermistor near inductor; 9–11µA current enables accurate thermal foldback of current limit. |
| PHASMD (Pin 12) | CLKOUT phase select | GND/INTVCC/floating configures 60°/120°/90° phase offset for synchronized multi-phase operation. |
| DIFFP, DIFFN (Pins 15,16) | Differential remote sense inputs | Direct connection to load point; 80kΩ input resistance and 2mV offset enable millivolt-level regulation accuracy. |
| DIFFOUT (Pin 17) | Differential amplifier output | Drives VFB through resistive divider; 2–3mA output capability supports standard feedback networks. |
| ISET (Pin 18) | Burst Mode / Stage Shedding threshold | Resistor-to-ground programs current foldback point and light-load mode transition level. |
| ILIM (Pin 19) | Current sense threshold select | GND/FLOAT/INTVCC selects max sense voltage: 25/45/68mV (E-grade), enabling adaptive current limiting. |
| MODE (Pin 20) | Operating mode selection | GND = forced continuous; FLOAT = Burst Mode; INTVCC = Stage Shedding - no external logic required. |
| PGOOD (Pin 21) | Power-good open-drain flag | Asserts after 20µs mask timer when VFB is within ±10% of 0.6V; supports system power sequencing. |
| CLKOUT (Pin 37) | Synchronization clock output | Phase-adjustable square wave; drives PLLIN of slave controllers for deterministic multi-phase timing. |
| PLLIN (Pin 38) | External clock synchronization input | Accepts external clock (e.g., system master oscillator) to align switching edges across multiple LTC3856 devices. |
| SGND (Pin 39, Exposed Pad) | Thermal & electrical ground plane | Mandatory PCB soldering required for rated θJA = 25°C/W and reliable current return path. |
Key Features
| Feature | Design Value |
|---|---|
| PolyPhase® dual-channel architecture | Reduces input/output capacitance by >50% and lowers RMS input current ripple versus single-phase solutions. |
| True remote sense differential amplifier | 0.997–1.003 V/V gain and 100dB PSRR eliminate PCB trace IR drop errors for sub-1% load regulation at point-of-load. |
| Programmable DCR temperature compensation | 9–11µA ITEMP current matches NTC characteristics, maintaining ±3% current limit accuracy from –40°C to 125°C. |
| Stage Shedding™ and Burst Mode® | Automatically transitions between 2-phase → 1-phase → sleep modes to maintain >85% efficiency down to 100mA load. |
| Active Voltage Positioning (AVP) | Programmable load-line droop (up to 2.5V) compensates for IR drop in high-current CPU/GPU rails without external circuitry. |
| Stackable for up to 12-phase operation | CLKOUT/PLLIN interface and PHASMD pin enable deterministic phase alignment across six LTC3856 ICs in master-slave topology. |
Applications
| Telecom Power Supply | Data Center Server VRM |
|---|---|
Use Scenario: 48V-to-1.5V conversion for 50A FPGA core rail in 1RU telecom switch with strict EMI limits. IC Role / Device Role / Timing Role: Dual-phase synchronous buck controller managing two parallel 25A phases with out-of-phase switching to suppress input ripple. Use Value: Achieves <36mV load-step overshoot and 95% peak efficiency while meeting EN55022 Class B conducted emissions without added filtering. |
Use Scenario: High-density 12-phase VRM supplying 1.0V/300A to dual-socket Xeon processors in hyperscale server. IC Role / Device Role / Timing Role: Master LTC3856EFE#PBF synchronizes five slave controllers via CLKOUT/PLLIN to distribute 300A across 12 phases with 30° phase shift. Use Value: Enables 12-phase scalability with single-point soft-start, AVP-based load-line tuning, and unified current balancing across all phases. |
| Industrial PLC Power Module | Medical Imaging System PSU |
Use Scenario: 24V-to-3.3V/20A isolated POL supply for real-time motion control FPGA in factory automation cabinet. IC Role / Device Role / Timing Role: Single LTC3856EFE#PBF configured in 2-phase mode with DCR sensing and Burst Mode for variable load (10mA–20A). Use Value: Maintains >90% efficiency from 100mA to full load; differential sensing ensures ±15mV regulation at load despite 150mm PCB trace length. |
Use Scenario: Low-noise 12V-to-1.2V/40A supply for MRI gradient coil driver ASIC requiring ultra-stable voltage during rapid field switching. IC Role / Device Role / Timing Role: LTC3856EFE#PBF operates in forced continuous mode with AVP and remote sensing to minimize transient-induced image artifacts. Use Value: Delivers <20mV load-step deviation and <10µVRMS output noise due to out-of-phase operation and differential feedback rejection. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual-phase synchronous buck controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| MP2950GQ-10 | Integrated MOSFET drivers only; no internal LDO; requires external 5V bias; fixed 600kHz fSW; no DCR tempco. | Targeted at cost-sensitive consumer SSDs; lacks remote sensing, AVP, and phase stacking support. | Choose MP2950GQ-10 only for space-constrained, low-complexity 12V-in applications where differential sensing and thermal current foldback are unnecessary. |
| ISL95836IRZ | Supports 3-phase operation natively; includes SMBus interface; higher quiescent current (12mA vs. 7mA); no Burst Mode. | Designed for Intel VR13/VR13.0 mobile CPUs; requires PMBus host; not suited for standalone industrial telecom use. | Choose ISL95836IRZ when PMBus telemetry, 3-phase native control, and Intel-compatible VID tables are mandatory - not for analog-only or non-Intel platforms. |
Compared with MP2950GQ-10 and ISL95836IRZ, the LTC3856EFE#PBF uniquely combines differential remote sensing, programmable DCR temperature compensation, AVP, and seamless 12-phase stacking - making it the only option for high-accuracy, thermally robust, multi-rail telecom and industrial POL systems requiring analog configurability and no digital interface overhead.
Availability
LTC3856EFE#PBF is available at Aetrix Electronics and suitable for telecom power supplies, data center VRMs, and industrial PLC power modules requiring stable component supply, long-term lifecycle assurance, and guaranteed -40°C to 125°C operation.
Supply support for LTC3856EFE#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 legacy of high-performance power management ICs with rigorous automotive and industrial qualification.
The LTC3856EFE#PBF belongs to Linear's PolyPhase® controller family, designed specifically for high-efficiency, multi-phase DC/DC conversion in telecom infrastructure, enterprise servers, and mission-critical industrial equipment where precision regulation and thermal resilience are paramount.
FAQ
What is the maximum supported switching frequency for the LTC3856EFE#PBF?
The LTC3856EFE#PBF supports a phase-lockable switching frequency range of 250kHz to 770kHz. At VFREQ = 2.4V or higher, the nominal frequency reaches 770kHz (typical), enabling compact magnetics and reduced output capacitance. The device maintains stable operation across this full range with consistent current-mode control loop behavior and minimal jitter.
Does the LTC3856EFE#PBF support remote voltage sensing, and how is it implemented?
Yes, the LTC3856EFE#PBF implements true remote voltage sensing via an integrated differential amplifier with DIFFP, DIFFN, and DIFFOUT pins. DIFFP connects directly to the load point, DIFFN to the return path, and DIFFOUT feeds the VFB pin through a resistive divider. This architecture achieves ±0.75% regulation accuracy independent of PCB trace resistance, critical for high-current POL applications.
How does the ILIM pin affect current limit behavior in the LTC3856EFE#PBF?
The ILIM pin on the LTC3856EFE#PBF selects one of three maximum current sense thresholds: 25mV (ILIM = GND), 45mV (ILIM = FLOAT), or 68mV (ILIM = INTVCC) for E-grade devices. This directly scales the peak inductor current per phase, enabling adaptive current limiting based on MOSFET RDS(ON), inductor DCR, and thermal constraints without changing external components.
Can the LTC3856EFE#PBF be used in single-phase configurations, and what design changes are needed?
Yes, the LTC3856EFE#PBF can operate in single-phase mode by connecting both TG1/TG2 and BG1/BG2 outputs in parallel and tying SENSE1+/SENSE2+ and SENSE1–/SENSE2– together. The MODE pin must be set to forced continuous (GND) or Burst Mode (floating), and PHASMD should be grounded. No firmware or external logic is required - all configuration remains analog and pin-strapped.
What thermal performance can be expected from the LTC3856EFE#PBF in its TSSOP package?
The LTC3856EFE#PBF in the 38-lead TSSOP (FE) package has a specified θJA of 25°C/W when the exposed pad (Pin 39) is properly soldered to a minimum 1-inch² copper pour. At 125°C maximum junction temperature and 25°C ambient, this allows up to ~4W of dissipation - sufficient for typical 2-phase 50A designs with efficient MOSFET selection and adequate airflow.
LTC3856EFE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- PolyPhase®
- Package/Case:
- 38-TFSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck
- Number of Outputs:
- 2
- Output Phases:
- 2
- Voltage - Supply (Vcc/Vdd):
- 4.5V ~ 38V
- Frequency - Switching:
- 250kHz ~ 770kHz
- Duty Cycle (Max):
- 94%
- Synchronous Rectifier:
- Yes
- Clock Sync:
- No
- Serial Interfaces:
- -
- Control Features:
- Current Limit, Enable, Frequency Control, Phase Control, Power Good, Soft Start, Tracking
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 38-TSSOP-EP
LTC3856EFE#PBF FAQ
1.How can I place an order for LTC3856EFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3856EFE#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 LTC3856EFE#PBF reliable?
The price and inventory of LTC3856EFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3856EFE#PBF is usually 5 days.
3.What payment methods are accepted for LTC3856EFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3856EFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3856EFE#PBF?
LTC3856EFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3856EFE#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 LTC3856EFE#PBF?
For technical support, including LTC3856EFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3856EFE#PBF requirements.
6.How does Aetrix verify that LTC3856EFE#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3856EFE#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 LTC3856EFE#PBF meets industry standards.
7.What is the process for return or replacement of LTC3856EFE#PBF?
All LTC3856EFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3856EFE#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 LTC3856EFE#PBF part is unused and in its original packaging.
Return procedure for LTC3856EFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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