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Analog Devices Inc. LTC3855IFE#TRPBF
- Part No.:
- LTC3855IFE#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 38-TFSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LTC3855IFE#TRPBF.pdf
- Description:
- IC REG CTRLR BUCK 38TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,975
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Product details
Overview
LTC3855IFE#TRPBF 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), ±0.75% 0.6 V reference accuracy, and supports up to 12-phase operation via CLKOUT/PHASMD. Used in high-current server VRMs and telecom intermediate bus converters.
For engineers reviewing the LTC3855IFE#TRPBF datasheet, LTC3855IFE#TRPBF pinout, LTC3855IFE#TRPBF application, or LTC3855IFE#TRPBF equivalent, key selection criteria include its 4.5 V–38 V input range, dual-channel independent soft-start/tracking, DCR temperature compensation, and phase-lockable 250 kHz–770 kHz switching frequency with true remote sense amplifier.
Technical Context
The LTC3855IFE#TRPBF implements two independent polyphase current-mode control loops with synchronized but anti-phase switching to reduce input ripple and EMI. Each channel uses a transconductance error amplifier (gm = 2 mmho), programmable ITH-based peak current limit, and precision 0.6 V feedback reference with ±0.75% accuracy over –40°C to 125°C.
Its integrated differential remote sense amplifier (gain = 0.998–1.002 V/V, GBW = 3 MHz, slew rate = 2 V/µs) enables accurate load regulation at 0.6 V–3.3 V outputs, while the MODE/PLLIN pin selects Burst Mode®, pulse-skipping, or forced continuous operation - each with distinct light-load efficiency and noise trade-offs.
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 28 V intermediate bus systems without external regulators. |
| Output Voltage Range | 0.6 V to 12.5 V (standard); 0.6 V to 3.3 V (with differential remote sense) - covers CPU core, memory, and I/O rail requirements. |
| Reference Voltage Accuracy | ±0.75% at 0.6 V - ensures tight output regulation under line/load/temperature variation for sensitive digital loads. |
| Switching Frequency Range | 250 kHz to 770 kHz (programmable via FREQ pin current) - balances efficiency, size, and EMI across wide load conditions. |
| Current Sense Threshold | 30 mV / 50 mV / 75 mV (set by ILIM1/ILIM2 pins) - enables low-loss DCR sensing or precision RSENSE with minimal power loss. |
| Operating Temperature | –40°C to +125°C junction - qualified for industrial and extended-temperature embedded power applications. |
| Differential Amplifier Gain | 0.998–1.002 V/V - delivers <±0.2% gain error for sub-10 mV remote sense voltage accuracy. |
Pinout & Package
Package: 38-lead plastic TSSOP (FE package) with exposed pad (Pin 39 = SGND). Thermal resistance θJA = 25°C/W. Exposed pad must be soldered to PCB for thermal and signal integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SENSE1+, SENSE1– | Channel 1 current sense differential inputs | Accept DCR network or discrete shunt; bias current ±1 µA minimizes error in low-RSENSE designs. |
| VFB1, VFB2 | Channel 1/2 feedback inputs | High-impedance (–15 nA bias) nodes for resistive divider connection; enable precise 0.6 V regulation. |
| TG1, TG2 / BG1, BG2 | Top/bottom gate drivers | Drive N-MOSFET gates with RDS(ON) ≤ 2.6 Ω (TG pull-up), 1.1 Ω (BG pull-down); support >15 A per phase. |
| DIFFP, DIFFN, DIFFOUT | Differential remote sense amplifier I/O | DIFFP connects to remote load point; DIFFOUT feeds VFB1/VFB2 via resistor divider for true Kelvin sensing. |
| CLKOUT, PHASMD | Multiphase synchronization interface | CLKOUT provides phase-adjustable clock (60°/90°/120°); PHASMD configures internal phase relationship for 2- or 3-phase interleaving. |
| ILIM1, ILIM2 | Current limit threshold select | Three-state logic (GND/FLOAT/INTVCC) sets max sense voltage to 30/50/75 mV - critical for DCR tempco calibration. |
Key Features
| Feature | Design Value |
|---|---|
| Dual 180° phased controllers | Reduces input capacitor RMS current by ~30% and lowers conducted EMI vs single-phase design. |
| Programmable DCR temperature compensation | ITEMP1/ITEMP2 pins accept NTC thermistors near inductors to correct DCR drift - maintains current limit accuracy over temperature. |
| True remote sensing differential amplifier | 0.998–1.002 V/V gain, 2 mV offset, 100 dB PSRR - enables <±5 mV load regulation at 3.3 V/20 A despite 50 mΩ PCB trace resistance. |
| Adjustable soft-start or VOUT tracking | TK/SS1/TK/SS2 pins accept external capacitor (soft-start) or resistor divider (tracking) - supports power sequencing for FPGAs and ASICs. |
| Foldback output current limiting | Current foldback reduces MOSFET stress during short-circuit events - protects power stage without external circuitry. |
Applications
| Server VRM Power Delivery | Telecom Intermediate Bus Converter |
|---|---|
Use Scenario: Dual-output 1.8 V/15 A and 1.2 V/15 A supply for multi-core x86 processors in 1U rack servers. IC Role / Device Role / Timing Role: Dual-channel synchronous buck controller with interleaved 180° phase shift and differential remote sense for load-point regulation. Use Value: Achieves >94% peak efficiency at full load and <±5 mV output deviation under 10 A transient steps via true remote sensing. |
Use Scenario: 48 V-to-12 V/30 A intermediate bus converter feeding downstream POL modules in 5G base station power shelves. IC Role / Device Role / Timing Role: High-input-voltage dual-phase controller operating at 500 kHz with DCR current sensing to minimize conduction loss. Use Value: Enables compact design using low-RDCR inductors and eliminates discrete current-sense resistors - reducing BOM cost and board area. |
| Industrial PLC I/O Power | Medical Imaging Power Sequencing |
Use Scenario: 24 V-to-5 V/10 A and 3.3 V/10 A dual-rail supply for isolated I/O modules in factory automation PLCs. IC Role / Device Role / Timing Role: Dual-controller with independent RUN1/RUN2 shutdown and TK/SS tracking for safe power-up/down sequencing. Use Value: Ensures strict 5 V → 3.3 V ramp timing compliance (<10 ms delay) and prevents latch-up during brownout recovery. |
Use Scenario: Precision dual-rail supply (1.2 V/2 A and 1.8 V/2 A) for FPGA-based image reconstruction engines in portable MRI subsystems. IC Role / Device Role / Timing Role: Controller with Burst Mode® operation and differential remote sense to meet <10 µVRMS noise spec at analog front-end. Use Value: Delivers <20 µVPP output ripple in Burst Mode and maintains <±0.5% regulation across –20°C to +70°C ambient. |
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 |
|---|---|---|---|
| LTC3857IUJ#TRPBF | 40-pin QFN package; higher fSW range (250 kHz–1 MHz); integrated EXTVCC LDO; no differential amplifier. | Preferred for space-constrained designs needing >770 kHz operation or where remote sense is unnecessary. | Select when board layout favors QFN thermal performance and differential sensing is not required for load regulation. |
| MP8765GL-Z | Single-chip dual-phase controller; fixed 0.6 V reference (±1%); no DCR tempco; 4.5 V–16 V input; no remote sense amplifier. | Suitable for cost-sensitive consumer applications with lower accuracy and temperature requirements. | Choose only for non-critical 12 V input systems where ±1% VOUT accuracy and –40°C to 85°C operation suffice. |
Compared with LTC3855IFE#TRPBF, LTC3857IUJ#TRPBF offers wider frequency tuning and better thermal dissipation but sacrifices differential remote sensing; MP8765GL-Z reduces system cost and complexity but lacks the precision, temperature range, and sensing flexibility needed for industrial/medical use.
Availability
LTC3855IFE#TRPBF is available at Aetrix Electronics and suitable for server VRMs, telecom power shelves, and industrial PLCs requiring stable component supply across extended temperature and long production lifecycles.
Supply support for LTC3855IFE#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 acquired Linear Technology in 2017 and maintains full product support, documentation, and manufacturing continuity for all Linear power ICs.
The LTC3855 belongs to Linear's high-performance polyphase controller family, designed specifically for high-efficiency, high-current, multi-rail DC/DC conversion in computing, communications, and industrial infrastructure.
FAQ
What is the maximum input voltage rating for the LTC3855IFE#TRPBF?
The LTC3855IFE#TRPBF has an absolute maximum input supply voltage (VIN) of 40 V, with recommended operating range from 4.5 V to 38 V. Exceeding 40 V risks permanent damage per Absolute Maximum Ratings. The device is commonly used with 12 V, 24 V, and 48 V intermediate bus systems after appropriate front-end conditioning.
Does the LTC3855IFE#TRPBF support true remote voltage sensing?
Yes, the LTC3855IFE#TRPBF integrates a dedicated differential remote sense amplifier (pins DIFFP, DIFFN, DIFFOUT) with 0.998–1.002 V/V gain, 2 mV offset, and 100 dB PSRR. This allows direct Kelvin connection to the load point, enabling precise regulation at the point-of-load - critical for low-voltage, high-current rails like 1.2 V CPU cores.
How is the switching frequency set on the LTC3855IFE#TRPBF?
The LTC3855IFE#TRPBF uses a precision 10 µA current source on the FREQ pin. A resistor from FREQ to SGND sets the oscillator frequency from 250 kHz (R = 0 Ω) to 770 kHz (R ≈ 120 kΩ). Alternatively, a DC voltage (0–2.4 V) applied directly to FREQ adjusts frequency linearly - enabling dynamic frequency scaling in adaptive power systems.
Can the LTC3855IFE#TRPBF operate with DCR current sensing only - no shunt resistor?
Yes, the LTC3855IFE#TRPBF is explicitly designed for DCR sensing: SENSE1+/SENSE1– and SENSE2+/SENSE2– accept low-voltage differential signals from inductor DCR networks. Its programmable 30/50/75 mV thresholds, ±1 µA sense pin bias, and integrated ITEMP1/ITEMP2 DCR temperature compensation make discrete shunts unnecessary in most high-current designs.
What is the purpose of the PHASMD pin on the LTC3855IFE#TRPBF?
The PHASMD pin configures relative phase alignment between the two internal controllers and the CLKOUT signal. Tied to GND/FLOAT/INTVCC, it selects 180°/180°/240° phase shift between channels and 60°/90°/120° CLKOUT phase - enabling seamless expansion to 3-, 6-, or 12-phase systems using multiple LTC3855IFE#TRPBF devices without external phase managers.
LTC3855IFE#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- PolyPhase®
- Package/Case:
- 38-TFSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tape & Reel (TR)
- 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#TRPBF FAQ
1.How can I place an order for LTC3855IFE#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3855IFE#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 LTC3855IFE#TRPBF reliable?
The price and inventory of LTC3855IFE#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3855IFE#TRPBF is usually 5 days.
3.What payment methods are accepted for LTC3855IFE#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3855IFE#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3855IFE#TRPBF?
LTC3855IFE#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3855IFE#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 LTC3855IFE#TRPBF?
For technical support, including LTC3855IFE#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3855IFE#TRPBF requirements.
6.How does Aetrix verify that LTC3855IFE#TRPBF is sourced from the original manufacturer or authorized distributors?
All LTC3855IFE#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 LTC3855IFE#TRPBF meets industry standards.
7.What is the process for return or replacement of LTC3855IFE#TRPBF?
All LTC3855IFE#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3855IFE#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 LTC3855IFE#TRPBF part is unused and in its original packaging.
Return procedure for LTC3855IFE#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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