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Analog Devices Inc. LT8705IFE#PBF
- Part No.:
- LT8705IFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 38-TFSOP (0.173", 4.40mm Width) 31 Leads, Exposed Pad
- Datasheet:
-
LT8705IFE#PBF.pdf
- Description:
- IC REG CTRLR BUCK-BOOST 38TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:1,201
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Product details
Overview
LT8705IFE#PBF from Analog Devices (formerly Linear Technology) is a synchronous 4-switch buck-boost DC/DC controller enabling single-inductor VIN-to-VOUT conversion where input voltage may be above, below, or equal to regulated output. It supports 2.8V–80V input and 1.3V–80V output ranges, integrates quad N-channel gate drivers, and delivers up to 98% efficiency in telecom voltage stabilizer and solar charge controller applications.
For engineers reviewing the LT8705IFE#PBF datasheet, LT8705IFE#PBF pinout, LT8705IFE#PBF application, or LT8705IFE#PBF equivalent, key selection considerations include its 38-pin TSSOP package with high-voltage isolation, programmable 100–400kHz switching frequency, integrated input/output current monitoring, and servo feedback loop status indication for system-level fault diagnostics.
Technical Context
The LT8705IFE#PBF implements a current-mode control architecture with four independent feedback loops-input voltage (FBIN), output voltage (FBOUT), input current (IMON_IN), and output current (IMON_OUT)-all referenced to a common VC error amplifier output. Its topology uses external N-MOSFETs in a 4-switch configuration, enabling seamless transition between buck, boost, and buck-boost operating regions without mode switching artifacts.
It features dedicated servo pins (SRVO_FBIN, SRVO_FBOUT, SRVO_IIN, SRVO_IOUT) that provide open-drain logic outputs indicating active regulation loops, and includes a synchronizable oscillator with 100–400kHz range, adjustable via RT resistor, plus CLKOUT for die temperature monitoring via duty cycle variation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VIN Range | 2.8V to 80V - supports wide-input systems including automotive cold-crank (6V), 48V telecom, and high-voltage solar arrays. |
| VOUT Range | 1.3V to 80V - enables direct regulation of battery stacks, PoE PSE, or industrial rails without intermediate stages. |
| Switching Frequency | 100kHz to 400kHz - adjustable via RT pin; allows optimization of size vs. EMI in high-power converters. |
| Gate Drivers | Quad N-channel drivers (TG1/BG1/TG2/BG2) - drives external MOSFETs with 20ns rise/fall times and <100ns dead-time control. |
| Efficiency | Up to 98% - achieved via synchronous rectification and low-loss current sensing with ±100mV differential input range. |
| Current Monitoring | Programmable IMON_IN/IMON_OUT - provides proportional analog current monitor outputs with 1.208V reference and 0.005%/V line regulation. |
| Package | 38-Lead Plastic TSSOP - modified for high-voltage operation; exposed pad tied to GND for thermal management (θJA = 25°C/W). |
Pinout & Package
LT8705IFE#PBF is housed in a 38-lead plastic TSSOP package (FE38 variant) with exposed thermal pad (Pin 39) soldered to PCB ground. The package is optimized for high-voltage isolation and thermal performance in industrial and telecom power supplies.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SHDN (Pin 4) | Shutdown Control Input | Active-low enable; pulls quiescent current to ≤1µA when grounded; must not float. |
| CSP/CSN (Pins 6/5) | Inductor Current Sense Inputs | Differential inputs for main current sense resistor; set current limit thresholds via VC voltage and internal gain (±100mV range). |
| FBIN/FBOUT (Pins 8/9) | Input & Output Voltage Feedback | High-impedance inputs (10nA bias) for resistor-divider feedback; regulate VIN or VOUT independently with 1.205V/1.207V references. |
| IMON_IN/IMON_OUT (Pins 3/10) | Current Monitor Outputs | Analog current-source outputs proportional to input/output current; 100µA full-scale, referenced to 1.208V. |
| VC (Pin 11) | Error Amplifier Output | Diode-AND node of EA1–EA4; connects external compensation network to stabilize all four regulation loops. |
| SYNC/CLKOUT (Pins 14/13) | Frequency Synchronization & Temp Monitor | SYNC accepts 0.5–1.3V logic for external clock sync; CLKOUT toggles at fOSC with duty cycle linearly tracking junction temperature. |
| TG1/BG1/TG2/BG2 (Pins 26/17/21/19) | N-Channel Gate Drivers | Drive external top/bottom MOSFETs; TGx swing from GATEVCC + SWx; BGx swing from GND to GATEVCC. |
| BOOST1/BOOST2 (Pins 28/20) | Floating Bootstrap Supplies | Connect to bootstrap capacitors; BOOST1 swings up to VIN + GATEVCC, BOOST2 up to VOUT + GATEVCC. |
| VIN/INTVCC/GATEVCC (Pins 38/1/18) | Power Supply Rails | VIN powers IC directly or via EXTVCC switchover; INTVCC regulates 6.35V for gate drivers; GATEVCC must tie to INTVCC. |
Key Features
| Feature | Design Value |
|---|---|
| Synchronous 4-switch topology | Enables continuous conduction across buck/boost/buck-boost regions without discontinuities or mode transitions. |
| Integrated quad feedback loops | Simultaneous regulation of input voltage, output voltage, input current, and output current - critical for solar MPPT and battery charging. |
| Servo status outputs | Four open-drain pins (SRVO_FBIN, SRVO_FBOUT, SRVO_IIN, SRVO_IOUT) indicate real-time active regulation loop - simplifies system-level fault logging. |
| Programmable operating modes | MODE pin selects forced CCM (<0.4V), Burst Mode (floating), or DCM (>2.3V) - optimizes light-load efficiency without compromising transient response. |
| High-voltage TSSOP package | FE38 variant includes enhanced creepage/clearance and modified layout for reliable operation up to 80V input/output differentials. |
| On-chip LDO and regulators | Includes 3.3V/12mA LDO (LDO33) and 6.35V/165mA INTVCC regulator - reduces external BOM count and improves startup robustness. |
Applications
| Solar Charge Controller | Telecom Voltage Stabilizer |
|---|---|
Use Scenario: Regulating variable PV array output (30–80V) to charge 48V battery bank while limiting input current during partial shading. IC Role / Device Role / Timing Role: Buck-boost controller managing bidirectional energy flow, enforcing input current limit and output voltage setpoint simultaneously. Use Value: Maintains >95% efficiency across 36–72V input range while providing precise 48V ±0.5% regulation and real-time IMON_IN feedback for MPPT algorithms. |
Use Scenario: Stabilizing -48V telecom distribution rail against upstream rectifier fluctuations and load transients in central office equipment. IC Role / Device Role / Timing Role: High-reliability buck-boost controller delivering constant 48V output from fluctuating -36V to -72V input sources. Use Value: Achieves 98% peak efficiency and sub-100µs load-step recovery using VC-loop bandwidth and servo-pinned fault detection for predictive maintenance. |
| Automotive 12V/48V Dual-Battery System | Industrial Battery Backup Converter |
Use Scenario: Bidirectional power transfer between 12V starter battery and 48V mild-hybrid storage in stop-start vehicles. IC Role / Device Role / Timing Role: Synchronous 4-switch controller supporting reverse current flow, input/output current limiting, and fast mode transitions. Use Value: Enables <200ns dead-time control and 100kHz–400kHz frequency agility to meet CISPR-25 EMI Class 5 requirements while maintaining <1% cross-regulation. |
Use Scenario: Providing uninterrupted 24V output from either 24V primary supply or 36V backup Li-ion stack in factory automation PLCs. IC Role / Device Role / Timing Role: Seamless switchover controller with dual FBIN/FBOUT regulation and programmable UVLO on both inputs. Use Value: Delivers <10ms switchover time and <50mV output droop using integrated IMON_IN/IMON_OUT monitoring and VC-based priority arbitration. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar buck-boost controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3780EFE#PBF | Fixed 100–600kHz frequency; no servo outputs; only input/output voltage feedback (no current loops); 28-pin TSSOP. | Lacks input/output current regulation and loop-status signaling - unsuitable for MPPT or current-limited telecom systems. | Select only if current monitoring and multi-loop control are unnecessary and higher frequency range is required. |
| MP2918GL-Z | Integrated MOSFETs (40V max); fixed 500kHz; no IMON/VC architecture; no servo pins; 20-pin QFN. | Not rated for >40V operation; lacks programmable frequency and high-side current sensing - limited to low-voltage DC-DC modules. | Only viable for compact, lower-power (<100W) designs where 80V capability and external FET control are not needed. |
Compared with LTC3780EFE#PBF and MP2918GL-Z, LT8705IFE#PBF uniquely combines 80V rating, four independent regulation loops, servo status outputs, and TSSOP packaging - making it the sole option for high-reliability, current-monitored buck-boost systems requiring field-serviceable FET replacement and real-time loop diagnostics.
Availability
LT8705IFE#PBF is available at Aetrix Electronics and suitable for telecom voltage stabilizers, solar charge controllers, and automotive 48V/12V bidirectional converters requiring stable component supply, long-term lifecycle support, and traceable sourcing from authorized channels.
Supply support for LT8705IFE#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 standards.
The LT8705IFE#PBF belongs to Linear's high-voltage buck-boost controller product line, designed specifically for applications demanding wide VIN/VOUT range, multi-parameter regulation, and robust operation in harsh environments like telecom infrastructure and renewable energy systems.
FAQ
What is the maximum input voltage rating for LT8705IFE#PBF?
The LT8705IFE#PBF supports an absolute maximum input voltage of 80V on the VIN pin, with guaranteed operation across 2.8V to 80V. This rating applies to both continuous operation and transient conditions, and the FE38 TSSOP package is specifically modified to ensure safe creepage and clearance at these voltages. The device also tolerates 81V on SW1/SW2 pins under normal switching conditions.
Does LT8705IFE#PBF support synchronous rectification and what is its peak efficiency?
Yes, LT8705IFE#PBF supports full synchronous rectification using external N-channel MOSFETs driven by its integrated quad gate drivers. Measured data shows peak efficiency of up to 98% in boost region (e.g., VIN=72V→VOUT=48V, IOUT=5A), enabled by low RDS(on) FET control, minimized gate drive losses, and precise dead-time management.
How does the VC pin function in LT8705IFE#PBF control architecture?
The VC pin in LT8705IFE#PBF serves as the diode-AND output node of four error amplifiers (EA1–EA4), combining input voltage, output voltage, input current, and output current regulation signals. External compensation components connect here to set loop bandwidth and stability margins for all four feedback paths simultaneously - a core feature enabling multi-parameter regulation without interaction.
Can LT8705IFE#PBF operate in Burst Mode and how is it enabled?
Yes, LT8705IFE#PBF supports Burst Mode operation for improved light-load efficiency. It is enabled by leaving the MODE pin floating (high-impedance), which configures the controller to enter burst cycles when load current drops below threshold. This mode reduces quiescent current to 2.65mA (typical) while maintaining output regulation and fast wake-up response.
What is the purpose of the SRVO_FBIN and SRVO_FBOUT pins on LT8705IFE#PBF?
The SRVO_FBIN and SRVO_FBOUT pins on LT8705IFE#PBF are open-drain logic outputs that go low when their respective feedback loops (input voltage and output voltage regulation) are actively controlling the VC node. These signals provide real-time status of loop engagement - useful for system-level diagnostics, fault logging, and adaptive control strategies without requiring additional ADC resources.
LT8705IFE#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 38-TFSOP (0.173", 4.40mm Width) 31 Leads, Exposed Pad
- Packaging:
- Tube
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Up/Step-Down
- Output Configuration:
- Positive
- Topology:
- Buck-Boost
- Number of Outputs:
- 2
- Output Phases:
- 2
- Voltage - Supply (Vcc/Vdd):
- 2.8V ~ 80V
- Frequency - Switching:
- 100kHz ~ 400kHz
- Duty Cycle (Max):
- -
- Synchronous Rectifier:
- Yes
- Clock Sync:
- Yes
- Serial Interfaces:
- -
- Control Features:
- Enable, Frequency Control, Soft Start
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 38-TSSOP-EP
LT8705IFE#PBF FAQ
1.How can I place an order for LT8705IFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT8705IFE#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 LT8705IFE#PBF reliable?
The price and inventory of LT8705IFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT8705IFE#PBF is usually 5 days.
3.What payment methods are accepted for LT8705IFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT8705IFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT8705IFE#PBF?
LT8705IFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT8705IFE#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 LT8705IFE#PBF?
For technical support, including LT8705IFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT8705IFE#PBF requirements.
6.How does Aetrix verify that LT8705IFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT8705IFE#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 LT8705IFE#PBF meets industry standards.
7.What is the process for return or replacement of LT8705IFE#PBF?
All LT8705IFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT8705IFE#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 LT8705IFE#PBF part is unused and in its original packaging.
Return procedure for LT8705IFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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