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Analog Devices Inc. LTC3856IUH#PBF
- Part No.:
- LTC3856IUH#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 32-WFQFN Exposed Pad
- Datasheet:
-
LTC3856IUH#PBF.pdf
- Description:
- IC REG CTRLR BUCK 32WFQFN
- Quantity:
- Payment:
- Shipping:
Inventory:4,140
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Product details
Overview
LTC3856IUH#PBF from Analog Devices (formerly Linear Technology) is a dual-channel, polyphase synchronous step-down DC/DC controller driving all-N-channel MOSFET stages for high-current 1.5V/50A power delivery. It features true remote differential voltage sensing, DCR or RSENSE current sensing with temperature compensation, phase-lockable 250–770kHz operation, and supports Burst Mode®, Stage Shedding™, and Active Voltage Positioning (AVP) in telecom and server VRMs.
For engineers reviewing the LTC3856IUH#PBF datasheet, LTC3856IUH#PBF pinout, LTC3856IUH#PBF application, or LTC3856IUH#PBF equivalent, key selection criteria include its ±0.75% 0.6V reference accuracy, 4.5V–38V input range, dual-phase interleaving for reduced ripple and EMI, and QFN-32 package thermal performance (θJA = 34°C/W).
Technical Context
The LTC3856IUH#PBF implements a constant-frequency current-mode control architecture with independent per-phase current sensing via SENSE1+/– and SENSE2+/– inputs, supporting DCR or discrete resistor sensing with programmable temperature compensation via ITEMP. Its differential amplifier (DIFFP/DIFFN/DIFFOUT) enables precise remote sensing across long PCB traces with 0.997–1.003 V/V gain and 2mV offset.
Phase synchronization is achieved through PLLIN and CLKOUT pins, allowing up to 12-phase stacking; PHASMD selects 60°, 90°, or 120° clock phase offsets. The controller integrates dual N-channel gate drivers (TG1/BG1/TG2/BG2) with 1.1–2.6Ω RDS(ON), minimum on-time of 90ns, and dropout recovery logic to maintain bootstrap capacitor (CB) charge during low-VIN operation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 4.5V to 38V - supports 5V, 12V, and 24V intermediate bus systems and wide battery chemistries. |
| Output Voltage Range | 0.6V to 5.0V without diffamp; 0.6V to 3.3V with diffamp - covers core CPU/GPU/ASIC supply rails. |
| Reference Accuracy | ±0.75% at 0.6V - ensures tight regulation under load transients and temperature variation. |
| Switching Frequency | 250kHz to 770kHz, phase-lockable - enables EMI reduction via synchronization and layout optimization. |
| Current Sensing | RSENSE or DCR with programmable tempco - maintains accurate current limit over –40°C to 125°C junction range. |
| Efficiency | Up to 95% at 1.5V/50A - achieved via low-RDS(ON) gate drive, interleaved phases, and light-load modes. |
| Package | 32-pin (5mm × 5mm) QFN with exposed SGND/PGND pad - provides low thermal resistance (θJA = 34°C/W). |
Pinout & Package
Package: 32-lead (5mm × 5mm) plastic QFN (UH package) with exposed thermal pad (Pin 33) soldered to SGND/PGND for electrical and thermal integrity. θJA = 34°C/W.
| Pin | Circuit Role | Design Meaning |
|---|---|---|
| TK/SS (Pin 1) | Soft-start / tracking control | Internal 1.25µA current charges external capacitor to ramp VOUT; enables output voltage tracking between supplies. |
| VFB (Pin 2) | Error amplifier feedback input | Compares divided output voltage (via DIFFOUT or resistive divider) against 0.6V reference to regulate VOUT. |
| ITH (Pin 3) | Error amplifier output / current threshold | Sets per-phase peak inductor current; voltage directly controls current comparator trip point. |
| AVP (Pin 4) | Active Voltage Positioning slope programming | Resistor to DIFFP sets load-line droop for VRM compliance; requires diffamp connection. |
| ITEMP (Pin 5) | DCR temperature compensation input | Connects to NTC thermistor near inductor to adjust current limit vs. temperature. |
| PHASMD (Pin 6) | CLKOUT phase select | GND/INTVCC/floating configures CLKOUT phase as 60°/120°/90° for multi-phase synchronization. |
| DIFFP (Pin 9) | Differential amp positive input | Must connect directly to remote load point (e.g., CPU VDD) for accurate sensing; used in AVP mode. |
| DIFFN (Pin 10) | Differential amp negative input | Connects to local ground side of output capacitors; completes Kelvin sense loop. |
| DIFFOUT (Pin 11) | Differential amp output | Drives VFB via resistive divider; enables remote sensing without adding error from PCB trace IR drop. |
| ISET (Pin 12) | Stage Shedding / Burst Mode threshold | Resistor to GND programs current threshold for phase shedding or burst entry. |
| ILIM (Pin 13) | Current sense threshold range select | GND/FLOAT/INTVCC selects max sense voltage: 23–37mV (I-grade), enabling fine-grained current limiting. |
| MODE (Pin 14) | Operating mode control | GND = forced continuous; INTVCC = Stage Shedding; floating = Burst Mode - determines light-load efficiency strategy. |
| PGOOD (Pin 15) | Power-good open-drain output | Pulled low when VFB deviates >±10% from target; includes 20µs debounce to avoid false triggers. |
| SW2 (Pin 16) | Channel 2 switch node | Connects to source of channel 2 low-side MOSFET and inductor; swings from ~–0.3V to VIN. |
| TG2 (Pin 17) | Channel 2 top-gate driver output | Drives gate of high-side N-MOSFET; floating output referenced to SW2 with INTVCC swing. |
| BOOST2 (Pin 18) | Channel 2 bootstrap supply | Connects to (+) terminal of bootstrap capacitor; swings up to VIN + INTVCC for high-side gate drive. |
| BG2 (Pin 19) | Channel 2 bottom-gate driver output | Drives gate of low-side N-MOSFET; referenced to PGND2 with INTVCC swing. |
| EXTVCC (Pin 20) | External bias supply input | Bypasses internal LDO when >4.7V applied; reduces power loss and heat in high-current designs. |
| INTVCC (Pin 21) | Internal 5V regulator output | Powers control circuitry; requires ≥4.7µF low-ESR capacitor to PGND for stability. |
| VIN (Pin 22) | Main input supply | Primary power input; decouple with 0.1–1µF ceramic cap close to pin and PGND. |
| TG1 (Pin 25) | Channel 1 top-gate driver output | Drives gate of channel 1 high-side N-MOSFET; identical function to TG2. |
| BOOST1 (Pin 24) | Channel 1 bootstrap supply | Identical function to BOOST2; connects to channel 1 bootstrap capacitor. |
| SW1 (Pin 26) | Channel 1 switch node | Identical function to SW2; connects to channel 1 inductor and low-side MOSFET source. |
| BG1 (Pin 23) | Channel 1 bottom-gate driver output | Drives gate of channel 1 low-side N-MOSFET; identical function to BG2. |
| PLLIN (Pin 28) | External clock synchronization input | Accepts external clock to lock internal oscillator frequency and phase - critical for multi-rail coherence. |
| CLKOUT (Pin 27) | Phase-adjustable clock output | Provides synchronized clock signal to other LTC3856 or compatible controllers for interleaving. |
| SENSE2+ (Pin 7) | Channel 2 current sense positive input | Connects to DCR network or sense resistor high side; paired with SENSE2– for current measurement. |
| SENSE2– (Pin 8) | Channel 2 current sense negative input | Connects to output node or sense resistor low side; forms differential pair with SENSE2+. |
| SENSE1+ (Pin 31) | Channel 1 current sense positive input | Same function as SENSE2+, dedicated to channel 1 current sensing path. |
| SENSE1– (Pin 32) | Channel 1 current sense negative input | Same function as SENSE2–, completing channel 1 current sense loop. |
| SGND (Pin 33) | Signal and power ground (exposed pad) | Thermally and electrically critical; must be soldered to PCB ground plane for performance and reliability. |
Key Features
| Feature | Design Value |
|---|---|
| PolyPhase® dual-channel interleaving | Reduces input/output ripple by ~70% vs. single-phase, lowering required capacitance and EMI filter size. |
| True remote differential sensing | Eliminates PCB trace IR drop error; maintains ±0.75% regulation accuracy at point-of-load under dynamic loads. |
| Programmable DCR temperature compensation | Uses ITEMP pin and external NTC to maintain stable current limit across –40°C to 125°C ambient. |
| Stackable for up to 12-phase operation | Enables scalable high-current solutions (e.g., 100A+) using multiple LTC3856IUH#PBF in master/slave configuration. |
| Three light-load efficiency modes | Burst Mode® (discontinuous), Stage Shedding™ (1→2 phase), or forced continuous - selectable via MODE pin. |
| Active Voltage Positioning (AVP) | Programmable load-line droop via AVP–DIFFP resistor; meets Intel VRM/IMVP specifications for CPU power delivery. |
Applications
| Telecom Base Station Power | Data Center Server VRM |
|---|---|
|
Use Scenario: High-density 48V-to-1.2V conversion for FPGA and ASIC cores in 5G radio units. IC Role / Device Role / Timing Role: Dual-phase synchronous buck controller managing 40A+ load with <100µs transient response. Use Value: Interleaved operation cuts input RMS current by 30%, reducing bulk capacitor stress and board area. |
Use Scenario: Point-of-load regulation for dual-socket Xeon processors requiring AVP-compliant droop. IC Role / Device Role / Timing Role: Primary VRM controller implementing IMVP-9/10 load-line specification via AVP pin. Use Value: Differential remote sensing maintains ±0.75% output accuracy despite 50mΩ PCB trace resistance. |
| Industrial PLC CPU Supply | Medical Imaging System DC-DC |
|
Use Scenario: 24V-to-3.3V/15A supply for real-time control CPUs operating in extended temperature ranges. IC Role / Device Role / Timing Role: Dual-phase controller with DCR sensing and ITEMP-based thermal derating. Use Value: Programmable current limit adapts to inductor heating, preventing thermal runaway during sustained loads. |
Use Scenario: Low-noise, high-reliability 12V-to-1.8V/30A supply for MRI subsystem FPGAs and ADCs. IC Role / Device Role / Timing Role: Synchronized multi-phase controller locked to system clock via PLLIN. Use Value: Phase-lockable 770kHz operation enables deterministic EMI placement outside sensitive band. |
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 |
|---|---|---|---|
| MP8770GQ-Z (Monolithic Power Systems) | Integrated power stage (MOSFETs + controller); 4.5–16V input; fixed 600kHz; no DCR sensing or AVP. | Lower BOM count for ≤25A designs; unsuitable for AVP-compliant CPU VRMs or >16V inputs. | Select when board space is constrained and input voltage is ≤16V; not a drop-in replacement for LTC3856IUH#PBF. |
| ISL95852IRZ-T (Renesas) | Single-chip 2-phase controller with integrated drivers; supports AVP and DCR sensing; 4.5–24V input; 300–1000kHz. | Similar feature set but lacks true differential remote sensing (only single-ended VOUT sense) and has lower max input voltage. | Consider for cost-sensitive industrial designs where differential sensing is not required and VIN ≤24V. |
Compared with MP8770GQ-Z and ISL95852IRZ-T, the LTC3856IUH#PBF uniquely delivers full differential remote sensing, 38V max input, and robust thermal compensation - making it preferred for high-reliability, high-accuracy, wide-input telecom and server applications.
Availability
LTC3856IUH#PBF is available at Aetrix Electronics and suitable for telecom base station power, data center server VRMs, and industrial PLC CPU supplies requiring stable component supply, long lifecycle support, and guaranteed −40°C to 125°C operation.
Supply support for LTC3856IUH#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 high-performance analog and power management portfolio with rigorous automotive- and industrial-grade qualification.
The LTC3856IUH#PBF belongs to Linear's PolyPhase® controller family, designed specifically for high-efficiency, multi-phase DC/DC conversion in demanding computing, networking, and infrastructure applications.
FAQ
What is the maximum input voltage rating for the LTC3856IUH#PBF?
The LTC3856IUH#PBF has an absolute maximum input voltage (VIN) rating of 40V, with recommended operating range from 4.5V to 38V. Exceeding 40V may cause permanent damage. This wide range supports 12V, 24V, and 48V intermediate bus architectures common in telecom and industrial systems.
Does the LTC3856IUH#PBF support remote voltage sensing, and how is it implemented?
Yes, the LTC3856IUH#PBF supports true remote differential voltage sensing using the DIFFP, DIFFN, and DIFFOUT pins. DIFFP connects to the load point (e.g., CPU VDD), DIFFN to the local ground return, and DIFFOUT feeds back into VFB - eliminating PCB trace IR drop error and maintaining ±0.75% regulation accuracy at point-of-load.
How does the LTC3856IUH#PBF achieve high efficiency at light loads?
The LTC3856IUH#PBF achieves high light-load efficiency via three selectable modes: Burst Mode® (discontinuous conduction), Stage Shedding™ (reducing active phases), or forced continuous conduction. Mode selection is controlled by the MODE pin. Burst Mode® reduces switching losses; Stage Shedding™ cuts driver and gate charge losses proportionally to load.
Can the LTC3856IUH#PBF be synchronized to an external clock, and which pins are involved?
Yes, the LTC3856IUH#PBF supports external clock synchronization via the PLLIN pin, which accepts an external clock signal to lock the internal oscillator frequency and phase. The CLKOUT pin provides a phase-adjustable output (60°/90°/120° selectable via PHASMD) for synchronizing additional LTC3856IUH#PBF or compatible controllers in multi-phase systems.
What thermal considerations apply to the LTC3856IUH#PBF in the 32-pin QFN package?
The LTC3856IUH#PBF in the UH (32-pin QFN) package has a junction-to-ambient thermal resistance (θJA) of 34°C/W. The exposed pad (Pin 33) must be soldered to a solid SGND/PGND copper plane for effective heat dissipation. Thermal design must account for power dissipation from gate drivers, INTVCC LDO, and internal circuitry under full load and worst-case ambient conditions.
LTC3856IUH#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- PolyPhase®
- Package/Case:
- 32-WFQFN 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:
- 32-QFN (5x5)
LTC3856IUH#PBF FAQ
1.How can I place an order for LTC3856IUH#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LTC3856IUH#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 LTC3856IUH#PBF reliable?
The price and inventory of LTC3856IUH#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LTC3856IUH#PBF is usually 5 days.
3.What payment methods are accepted for LTC3856IUH#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LTC3856IUH#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LTC3856IUH#PBF?
LTC3856IUH#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LTC3856IUH#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 LTC3856IUH#PBF?
For technical support, including LTC3856IUH#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LTC3856IUH#PBF requirements.
6.How does Aetrix verify that LTC3856IUH#PBF is sourced from the original manufacturer or authorized distributors?
All LTC3856IUH#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 LTC3856IUH#PBF meets industry standards.
7.What is the process for return or replacement of LTC3856IUH#PBF?
All LTC3856IUH#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LTC3856IUH#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 LTC3856IUH#PBF part is unused and in its original packaging.
Return procedure for LTC3856IUH#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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