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Analog Devices Inc. LT8705EFE#TRPBF
- Part No.:
- LT8705EFE#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 38-TFSOP (0.173", 4.40mm Width) 31 Leads, Exposed Pad
- Datasheet:
-
LT8705EFE#TRPBF.pdf
- Description:
- IC REG CTRLR BUCK-BOOST 38TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:3,655
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Product details
Overview
LT8705EFE#TRPBF from Analog Devices (formerly Linear Technology) is a synchronous 4-switch buck-boost DC/DC controller IC designed for wide-input, wide-output voltage regulation in high-reliability power systems. It supports input voltages from 2.8V to 80V and output voltages from 1.3V to 80V, features integrated quad N-channel MOSFET gate drivers, and delivers up to 98% efficiency in synchronous rectification mode - used in telecom voltage stabilizers and solar charge controllers where VIN may be above, below, or equal to VOUT.
For engineers reviewing the LT8705EFE#TRPBF datasheet, LT8705EFE#TRPBF pinout, LT8705EFE#TRPBF application, or LT8705EFE#TRPBF equivalent, key selection considerations include its 38-lead TSSOP package with high-voltage modifications, programmable 100kHz–400kHz switching frequency via RT resistor, dual current monitoring (IMON_IN/IMON_OUT), and four independent feedback loops (input/output voltage and current) enabling precise source-sink power management in bidirectional energy systems.
Technical Context
The LT8705EFE#TRPBF implements a current-mode control architecture with diode-ANDed error amplifiers (EA1–EA4) on the VC pin, enabling seamless transition between buck, boost, and buck-boost operating regions without mode switching artifacts. Its servo pins (SRVO_FBIN, SRVO_FBOUT, SRVO_IIN, SRVO_IOUT) provide real-time status of active regulation loops, supporting dynamic load and source management.
It integrates dedicated current-sense amplifiers for both input (CSPIN/CSNIN) and output (CSPOUT/CSNOUT) paths, each with 1.208V regulation reference and ±100mV differential input range, plus programmable overcurrent thresholds. The controller supports Burst Mode® operation, discontinuous conduction mode (DCM), and forced continuous conduction mode (CCM) selected via the MODE pin - critical for optimizing light-load efficiency in battery-powered telecom infrastructure.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VIN Range | 2.8V to 80V - supports automotive cold-crank (≥4.5V), solar MPPT (up to 80V PV string), and telecom -48V systems with reverse polarity protection. |
| VOUT Range | 1.3V to 80V - enables single-controller solutions for 3.3V/5V/12V/24V/48V rails and high-voltage battery charging (e.g., 52V e-bike packs). |
| Switching Frequency | 100kHz to 400kHz - set by RT resistor; allows optimization of magnetics size vs. EMI performance in space-constrained industrial designs. |
| Efficiency | Up to 98% - achieved via synchronous rectification and low-loss gate drivers (20ns rise/fall), reducing thermal load in sealed enclosures. |
| Feedback Loops | 4 independent loops (FBIN, FBOUT, IMON_IN, IMON_OUT) - enables simultaneous input current limiting, output voltage regulation, and output current limiting for battery charge/discharge safety. |
| Package | 38-lead TSSOP with high-voltage modification - rated for 125°C junction temperature; exposed pad soldered to PCB for thermal reliability in continuous 5A+ applications. |
| LDO Outputs | 6.35V INTVCC (127mA max) and 3.3V LDO33 (17.25mA max) - powers gate drivers and external bias circuitry without auxiliary supplies. |
Pinout & Package
LT8705EFE#TRPBF uses a 38-lead plastic TSSOP package (FE38 variant) with exposed GND pad (Pin 39) requiring PCB soldering for thermal and electrical integrity. Pin numbering follows standard TSSOP top-view layout with high-voltage isolation enhancements.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SHDN (Pin 4) | Shutdown control input | Active-high enable; <1µA shutdown current enables ultra-low-power standby in remote IoT gateways. |
| CSPIN/CSNIN (Pins 37/36) | Input current sense differential inputs | Measure voltage across RSENSE1 to regulate input current - critical for solar input current limiting and input overcurrent protection. |
| CSPOUT/CSNOUT (Pins 34/32) | Output current sense differential inputs | Monitor output current via RSENSE2; enables constant-current battery charging or LED driver operation. |
| FBIN/FBOUT (Pins 8/9) | Input/output voltage feedback inputs | Connect to resistor dividers for independent VIN and VOUT regulation - essential for bidirectional power flow control. |
| VC (Pin 11) | Error amplifier output | Diode-AND node of EA1–EA4 outputs; compensation network here sets loop stability across all operating modes. |
| TG1/BG1, TG2/BG2 (Pins 26/17, 21/19) | Top/bottom gate drivers | Drive external N-MOSFETs in 4-switch topology; 20ns switching transitions minimize shoot-through risk at 400kHz. |
| SW1/SW2 (Pins 24/22) | Switch node connections | Interface directly to MOSFET sources; rated for 81V transient - supports 48V system derating with margin. |
| INTVCC/GATEVCC (Pins 1/18) | Internal gate driver supply | 6.35V regulated output; must be connected to GATEVCC and bypassed with ≥4.7µF ceramic capacitor for driver stability. |
Key Features
| Feature | Design Value |
|---|---|
| Synchronous 4-switch topology | Enables single-inductor buck-boost conversion with >95% efficiency across full VIN/VOUT crossover region - eliminates need for separate buck + boost stages. |
| Programmable operating mode | MODE pin selects Burst Mode® (low IQ), DCM (light-load efficiency), or forced CCM (low-noise, fixed-frequency) - adapts to varying load profiles in telecom line cards. |
| Dual current monitoring | Independent IMON_IN and IMON_OUT pins provide analog current-proportional outputs - simplifies system-level current telemetry and closed-loop battery management. |
| Integrated gate drivers | Quad N-MOSFET drivers with 20ns rise/fall times support high-frequency operation up to 400kHz - reduces inductor size and improves transient response in 48V server PSUs. |
| High-voltage TSSOP package | FE38 package includes enhanced creepage/clearance and modified bonding - certified for 80V continuous operation in industrial motor drives and EV auxiliary power units. |
Applications
| Solar Charge Controller | Telecom Voltage Stabilizer |
|---|---|
Use Scenario: Regulating variable PV array voltage (20–75V) to charge a 48V lithium battery bank while limiting input current during partial shading. IC Role / Device Role / Timing Role: Buck-boost controller managing bidirectional power flow; uses FBIN for MPPT voltage tracking and IMON_IN for input current capping. Use Value: Maintains >96% efficiency across 36–72V input range while enforcing 10A max input current - prevents inverter overload and extends battery cycle life. | Use Scenario: Stabilizing -48V telecom distribution rail against upstream rectifier fluctuations and downstream load transients in central office equipment. IC Role / Device Role / Timing Role: High-efficiency DC/DC controller maintaining tight 48V ±0.5% output under 0–20A step loads using FBOUT and IMON_OUT feedback. Use Value: Delivers 97.5% peak efficiency at 15A and <100µs transient recovery - meets GR-1089 immunity requirements for telecom infrastructure. |
| Automotive 12V/48V Bi-Directional Converter | Industrial Battery Backup System |
Use Scenario: Enabling power transfer between legacy 12V vehicle systems and new 48V mild-hybrid architectures during engine start-stop cycles. IC Role / Device Role / Timing Role: Synchronous buck-boost controller operating in both directions; uses SRVO pins to indicate active regulation loop during voltage reversal. Use Value: Supports 12V ↔ 48V conversion with <2% output droop at 30A and <500ms fault recovery - satisfies ISO 16750-2 pulse test requirements. | Use Scenario: Providing seamless switchover between AC mains and 24V lead-acid backup battery in industrial PLC power supplies during grid outages. IC Role / Device Role / Timing Role: Dual-loop regulator controlling output voltage (FBOUT) and battery charge current (IMON_OUT) simultaneously during transition events. Use Value: Achieves zero-output-interruption switchover with <10ms delay and maintains ±0.2% VOUT regulation - ensures deterministic PLC operation per IEC 61131-2. |
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 | Same 38-lead TSSOP package; 4V–36V VIN range; no IMON_IN/IMON_OUT pins; fixed 100kHz–600kHz frequency. | Limited to lower-voltage industrial systems; lacks dual current monitoring for battery charge control. | Select when VIN ≤36V and only output current monitoring is required - reduces BOM count but sacrifices input-side protection. |
| MPQ4333GJ-AEC1-Z | Automotive-grade 3.5V–36V buck-boost controller; integrated MOSFETs; 500kHz max frequency; AEC-Q100 qualified. | Not suitable for >36V systems; no servo pins or independent input current sensing; limited to passenger vehicle ECUs. | Choose for cost-sensitive automotive body electronics where 48V compatibility and external FET control are unnecessary. |
Compared with LTC3780EFE#PBF and MPQ4333GJ-AEC1-Z, the LT8705EFE#TRPBF uniquely supports 80V operation, provides four independent feedback loops, and includes servo outputs for real-time loop status - making it the only option for high-voltage solar, telecom, and bidirectional 48V industrial systems requiring comprehensive power path control.
Availability
LT8705EFE#TRPBF is available at Aetrix Electronics and suitable for solar charge controllers, telecom voltage stabilizers, and automotive 12V/48V bi-directional converters requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT8705EFE#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 its high-performance power management portfolio with rigorous automotive and industrial qualification standards.
The LT8705EFE#TRPBF belongs to the LT87xx family of synchronous 4-switch buck-boost controllers, engineered specifically for high-voltage, high-reliability power conversion in telecom infrastructure, renewable energy systems, and next-generation automotive electrification platforms.
FAQ
What is the maximum input voltage rating for the LT8705EFE#TRPBF?
The LT8705EFE#TRPBF has an absolute maximum input voltage rating of 80V on the VIN and EXTVCC pins, with guaranteed operation across a 2.8V to 80V input range. This enables direct interface with unregulated solar arrays, 48V telecom rectifiers, and industrial 60V DC distribution buses without external pre-regulation - a key differentiator versus lower-voltage buck-boost controllers like the LTC3780.
Does the LT8705EFE#TRPBF support bidirectional power flow?
The LT8705EFE#TRPBF does not natively support true bidirectional power flow in a single configuration. It operates as a unidirectional buck-boost controller regulating power from VIN to VOUT. However, its ability to maintain regulation when VIN is above, below, or equal to VOUT - combined with independent FBIN and FBOUT feedback - allows system-level implementation of bidirectional energy transfer using external control logic and complementary FETs, as documented in Linear Application Note 126.
How is the switching frequency set on the LT8705EFE#TRPBF?
The switching frequency of the LT8705EFE#TRPBF is set by an external resistor connected from the RT pin (Pin 15) to ground. With RT = 215kΩ, the typical frequency is 202kHz; RT = 365kΩ yields ~120kHz, and RT = 124kΩ gives ~350kHz. The device also supports external synchronization via the SYNC pin, accepting TTL/CMOS clocks from 100kHz to 400kHz with 20%–80% duty cycle tolerance - critical for EMI reduction in dense PCB layouts.
What is the purpose of the SRVO_FBIN and SRVO_FBOUT pins on the LT8705EFE#TRPBF?
The SRVO_FBIN and SRVO_FBOUT pins on the LT8705EFE#TRPBF are open-drain logic outputs that indicate which voltage regulation loop is actively controlling the converter. SRVO_FBIN pulls low when the input voltage feedback loop (FBIN) is dominant - such as during input current limiting - while SRVO_FBOUT pulls low when the output voltage loop (FBOUT) is active. These signals enable external microcontrollers to monitor real-time regulation state and implement adaptive system-level protection algorithms.
Can the LT8705EFE#TRPBF operate with only output voltage feedback?
Yes, the LT8705EFE#TRPBF can operate with only output voltage feedback by connecting the FBOUT pin to a resistor divider from VOUT and leaving FBIN, IMON_IN, and IMON_OUT unconnected (with appropriate pull-up/down as specified). In this configuration, it functions as a standard buck-boost controller regulating only VOUT. However, disabling input feedback forfeits input current limiting and input overvoltage protection - features that require FBIN and CSPIN/CSNIN connections to be fully utilized in the LT8705EFE#TRPBF design.
LT8705EFE#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 38-TFSOP (0.173", 4.40mm Width) 31 Leads, Exposed Pad
- Packaging:
- Tape & Reel (TR)
- 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
LT8705EFE#TRPBF FAQ
1.How can I place an order for LT8705EFE#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT8705EFE#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 LT8705EFE#TRPBF reliable?
The price and inventory of LT8705EFE#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT8705EFE#TRPBF is usually 5 days.
3.What payment methods are accepted for LT8705EFE#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT8705EFE#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT8705EFE#TRPBF?
LT8705EFE#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT8705EFE#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 LT8705EFE#TRPBF?
For technical support, including LT8705EFE#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT8705EFE#TRPBF requirements.
6.How does Aetrix verify that LT8705EFE#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT8705EFE#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 LT8705EFE#TRPBF meets industry standards.
7.What is the process for return or replacement of LT8705EFE#TRPBF?
All LT8705EFE#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT8705EFE#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 LT8705EFE#TRPBF part is unused and in its original packaging.
Return procedure for LT8705EFE#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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