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Analog Devices Inc. LTC3855IFE#PBF
- Part No.:
- LTC3855IFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 38-TFSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LTC3855IFE#PBF.pdf
- Description:
- IC REG CTRLR BUCK 38TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:100
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Product details
Overview
LTC3855IFE#PBF from Analog Devices (formerly Linear Technology) is a dual, 180° out-of-phase, current-mode synchronous step-down DC/DC controller driving all-N-channel MOSFET stages. It features differential remote sensing, programmable current sense thresholds (30/50/75 mV), 0.6 V ±0.75% reference accuracy, and supports up to 12-phase operation via CLKOUT/PHASMD. Designed for high-current server VRMs and telecom intermediate bus converters, it delivers up to 95% efficiency across 4.5 V–38 V input and 0.6 V–12.5 V output ranges.
For engineers reviewing the LTC3855IFE#PBF datasheet, LTC3855IFE#PBF pinout, LTC3855IFE#PBF application, or LTC3855IFE#PBF equivalent, key selection considerations include its dual-channel phase interleaving for input capacitor reduction, DCR temperature compensation for inductor current sensing stability, differential remote sense amplifier bandwidth (3 MHz GBW), and –40°C to +125°C industrial temperature grade.
Technical Context
The LTC3855IFE#PBF implements two independent PolyPhase® current-mode control loops with synchronized but 180° phase-shifted switching, reducing input ripple current and enabling smaller bulk capacitance. Each channel uses a transconductance error amplifier (gm = 2 mmho) and a precision 0.6 V reference with ±0.75% accuracy over temperature.
Its integrated differential remote sense amplifier (gain = 0.998–1.002 V/V, PSRR = 100 dB, slew rate = 2 V/µs) enables accurate load regulation at point-of-load, while programmable ILIM pins set maximum sense voltage per channel (30/50/75 mV), supporting both discrete resistors and DCR sensing with temperature compensation via ITEMP1/ITEMP2 inputs.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4.5 V to 38 V - supports 5 V, 12 V, 24 V, and 36 V intermediate bus systems without external regulators. |
| Output Voltage Range | 0.6 V to 12.5 V - covers core logic (0.6–1.8 V), I/O (1.2–3.3 V), and auxiliary rails (5 V, 12 V). |
| Reference Accuracy | ±0.75% at 0.6 V - ensures tight output regulation under line/load/temperature variation for CPU/GPU VRMs. |
| Oscillator Frequency | 250 kHz to 770 kHz - adjustable via FREQ pin current (10 µA); enables optimization of size vs. efficiency trade-offs. |
| Current Sense Threshold | Programmable: 30/50/75 mV - allows use of low-value DCR or sense resistors while minimizing power loss. |
| Differential Sense Bandwidth | 3 MHz GBW, 2 V/µs slew rate - maintains fast transient response and stable regulation under dynamic load steps. |
| Operating Temperature | –40°C to +125°C junction - qualified for industrial and telecom base station environments with full spec guarantee. |
Pinout & Package
The LTC3855IFE#PBF is housed in a 38-lead plastic TSSOP (FE package) with exposed pad (Pin 39 = SGND), requiring PCB soldering for thermal and signal integrity. Pin count and layout match Linear's standard FE footprint for drop-in compatibility with existing designs.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SENSE1+, SENSE1– SENSE2+, SENSE2– |
Current sense comparator inputs | Accept differential voltage from DCR network or sense resistor; bias current ±1 µA minimizes error at low currents. |
| VFB1, VFB2 | Error amplifier feedback inputs | Receive remote-sensed output voltage via resistive divider; input current ≤ –50 nA preserves divider accuracy. |
| DIFFP, DIFFN, DIFFOUT | Differential remote sense amplifier I/O | Enable Kelvin connection to load: DIFFP to remote VOUT+, DIFFN to local ground, DIFFOUT feeds VFB with 1× gain. |
| TG1, TG2 / BG1, BG2 | Top/bottom gate drivers | Drive N-MOSFET gates with 2.6 Ω pull-up / 1.5 Ω pull-down RDS(ON); support >1 MHz switching with <25 ns transition times. |
| ILIM1, ILIM2 | Current limit threshold select | Set max sense voltage: GND = 30 mV, float = 50 mV, INTVCC = 75 mV - configures sensing element without external components. |
| PHASMD, CLKOUT | Multiphase synchronization interface | PHASMD selects relative phase (0°/180°/240°); CLKOUT provides sync clock with programmable phase (60°/90°/120°) for 12-phase expansion. |
Key Features
| Feature | Design Value |
|---|---|
| Dual 180° interleaved controllers | Reduces RMS input ripple current by ~70%, allowing 40% smaller input capacitors and lower ESR requirements. |
| Programmable DCR temperature compensation | Uses ITEMP1/ITEMP2 inputs with external NTC thermistors to maintain constant current sense gain across –40°C to +125°C. |
| Burst Mode®, pulse-skipping, and forced continuous modes | Enables >90% efficiency at 10 mA load (Burst), low-noise operation at medium loads (pulse-skip), and minimal output ripple at full load (CCM). |
| True remote sensing differential amplifier | 0.998–1.002 V/V gain, 2 mV offset, and 100 dB PSRR ensure ±1% load regulation at point-of-load despite PCB IR drop. |
| Integrated EXTVCC switchover | Automatically bypasses internal LDO when EXTVCC > 4.7 V, reducing power loss and enabling efficient self-biasing from output rail. |
Applications
| Server CPU Voltage Regulator Modules | Telecom Intermediate Bus Converters |
|---|---|
Use Scenario: High-current, dynamically scaled core voltage delivery for multi-core Xeon/EPYC processors with rapid load transients up to 100 A/µs. IC Role / Device Role / Timing Role: Dual-channel PolyPhase® controller managing parallel buck stages with interleaved timing to minimize input/output ripple and enable fast transient response. Use Value: Achieves <1% output deviation during 50 A step with 1.2 V ±15 mV tolerance, leveraging differential remote sense and 0.6 V ±0.75% reference. |
Use Scenario: Converting 48 V or 24 V telecom bus to 12 V or 5 V distribution rails in base station power shelves with strict efficiency and thermal constraints. IC Role / Device Role / Timing Role: Primary controller for high-efficiency, wide-input-range DC/DC conversion with phase interleaving to reduce input capacitor stress and EMI. Use Value: Delivers 94% peak efficiency at 20 A/12 V from 36 V input, enabled by 4.5 V–38 V VIN range, low RDS(ON) gate drivers, and programmable 250–770 kHz frequency. |
| Industrial PLC Power Supplies | Medical Imaging System Auxiliary Rails |
Use Scenario: Generating isolated 3.3 V, 5 V, and ±15 V rails from 24 V DC input in ruggedized programmable logic controllers operating in extended temperature environments. IC Role / Device Role / Timing Role: Dual-output synchronous buck controller providing tightly regulated, independently tracked outputs with soft-start sequencing and power-good monitoring. Use Value: Ensures reliable startup and fault immunity via dual PGOOD signals, –40°C to +125°C guaranteed operation, and foldback current limiting protecting against short-circuit faults. |
Use Scenario: Powering low-noise analog front-ends (AFE), ADCs, and FPGA configuration circuits in MRI/PET detector modules where EMI and voltage stability are critical. IC Role / Device Role / Timing Role: Low-ripple, low-EMI dual buck controller operating in forced continuous mode with differential remote sensing to eliminate PCB trace resistance errors. Use Value: Maintains <50 µVpp output noise and ±0.5% regulation at load, enabled by Burst Mode disable, 3 MHz differential amp GBW, and precision 0.6 V reference. |
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 |
|---|---|---|---|
| MP2950A from Monolithic Power Systems | Single-chip dual-phase controller with integrated MOSFET drivers; lacks differential remote sense amplifier and DCR tempco. | Suitable for cost-sensitive, space-constrained designs where remote sensing is not required and temperature drift is mitigated externally. | Choose MP2950A for simplified BOM and smaller footprint; choose LTC3855IFE#PBF when point-of-load regulation accuracy and DCR-based sensing stability are mandatory. |
| ISL95831 from Renesas | Supports up to 4-phase operation and Intel VR13/VR14 compliance; includes SMBus interface and telemetry, but no programmable sense threshold. | Targeted at client CPU VRMs with digital interface requirements; not rated for >125°C operation. | Choose ISL95831 for digitally managed, multi-phase client platforms; choose LTC3855IFE#PBF for analog-controlled, high-temp industrial/telecom systems needing flexible current sensing. |
Compared with MP2950A and ISL95831, the LTC3855IFE#PBF uniquely combines guaranteed –40°C to +125°C operation, hardware-programmable current sense thresholds, and a dedicated differential remote sense amplifier-making it optimal for high-reliability analog-regulated power systems where precision and thermal robustness are non-negotiable.
Availability
LTC3855IFE#PBF is available at Aetrix Electronics and suitable for server CPU VRMs, telecom intermediate bus converters, and industrial PLC power supplies requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LTC3855IFE#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 full product support, documentation, and manufacturing continuity for the LTC portfolio.
The LTC3855 belongs to Linear's high-performance analog power controller family, designed specifically for high-efficiency, multiphase, synchronous buck conversion in demanding computing, communications, and industrial infrastructure applications.
FAQ
What is the operating temperature range guaranteed for the LTC3855IFE#PBF?
The LTC3855IFE#PBF is specified and guaranteed over a junction temperature range of –40°C to +125°C. This industrial-grade rating is confirmed in the Absolute Maximum Ratings table and Electrical Characteristics notes, with full parameter performance assured across this range-not just characterized or designed to meet it.
How does the LTC3855IFE#PBF implement differential remote sensing?
The LTC3855IFE#PBF uses dedicated DIFFP, DIFFN, and DIFFOUT pins to form a high-precision differential amplifier (gain = 0.998–1.002 V/V, 2 mV offset, 100 dB PSRR). DIFFP connects directly to the remote load positive node, DIFFN to the local output capacitor ground, and DIFFOUT feeds VFB1 or VFB2-enabling true Kelvin regulation independent of PCB trace resistance.
Can the LTC3855IFE#PBF be configured for single-channel operation?
Yes, the LTC3855IFE#PBF supports independent channel enable/disable via RUN1 and RUN2 pins. Either channel can be disabled by pulling its RUN pin below 1.2 V, allowing the remaining channel to operate fully-including its full 0.6 V–12.5 V output range, differential sensing, and phase-lock capability-without firmware or external logic.
What are the supported switching frequency ranges for the LTC3855IFE#PBF?
The LTC3855IFE#PBF offers a programmable oscillator frequency from 250 kHz (VFREQ = 0 V) to 770 kHz (VFREQ ≥ 2.4 V), with nominal 500 kHz at VFREQ = 1.2 V. Frequency is set by a resistor from FREQ pin to SGND, sourcing a precise 10 µA current-enabling stable, jitter-free operation without external crystals or timing capacitors.
Does the LTC3855IFE#PBF support DCR current sensing with temperature compensation?
Yes, the LTC3855IFE#PBF supports DCR current sensing with hardware-based temperature compensation using ITEMP1 and ITEMP2 pins. Connecting external NTC thermistors near the inductors allows automatic adjustment of the current sense gain to counteract copper DCR drift, maintaining accuracy across –40°C to +125°C without software or calibration.
LTC3855IFE#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):
- 95%
- 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
LTC3855IFE#PBF FAQ
1.How can I place an order for LTC3855IFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3855IFE#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 LTC3855IFE#PBF reliable?
The price and inventory of LTC3855IFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3855IFE#PBF is usually 5 days.
3.What payment methods are accepted for LTC3855IFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3855IFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3855IFE#PBF?
LTC3855IFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3855IFE#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 LTC3855IFE#PBF?
For technical support, including LTC3855IFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3855IFE#PBF requirements.
6.How does Aetrix verify that LTC3855IFE#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3855IFE#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 LTC3855IFE#PBF meets industry standards.
7.What is the process for return or replacement of LTC3855IFE#PBF?
All LTC3855IFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3855IFE#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 LTC3855IFE#PBF part is unused and in its original packaging.
Return procedure for LTC3855IFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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