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Analog Devices Inc. LT8705AIFE#PBF
- Part No.:
- LT8705AIFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 38-TFSOP (0.173", 4.40mm Width) 31 Leads, Exposed Pad
- Datasheet:
-
LT8705AIFE#PBF.pdf
- Description:
- IC REG CTRLR BUCK-BOOST 38TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:882
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Product details
Overview
LT8705AIFE#PBF from Analog Devices (formerly Linear Technology) is a synchronous 4-switch buck-boost DC/DC controller supporting input and output voltages from 2.8V to 80V. It integrates input/output voltage and current feedback loops, features quad N-channel MOSFET gate drivers, and operates in burst, discontinuous, or forced continuous conduction mode. It is used in high-voltage solar charge controllers and telecom voltage stabilizers.
For engineers reviewing the LT8705AIFE#PBF datasheet, LT8705AIFE#PBF pinout, LT8705AIFE#PBF application, or LT8705AIFE#PBF equivalent, key selection considerations include its 38-lead TSSOP package, –40°C to 125°C operating junction temperature, integrated 3.3V/12mA LDO, synchronizable 100–400kHz switching frequency, and support for single-inductor buck-boost topologies with up to 98% efficiency.
Technical Context
The LT8705AIFE#PBF implements a current-mode control architecture with four independent error amplifiers (EA1–EA4) managing output voltage (FBOUT), input voltage (FBIN), output current (IMON_OUT), and input current (IMON_IN) regulation. Its VC pin serves as the diode-AND of all four amplifier outputs, directly controlling peak inductor current via CSP/CSN sensing.
It supports three distinct operating modes selected by the MODE pin: forced continuous conduction mode (FCM) below 0.4V, Burst Mode® when floating, and discontinuous conduction mode (DCM) above 2.3V. The controller includes dedicated open-drain status pins (SRVO_FBIN, SRVO_FBOUT, etc.) only available in QFN packages - not present in the TSSOP-based LT8705AIFE#PBF.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VIN Range | 2.8V to 80V; enables direct interface with 24V/48V/72V industrial, solar, and automotive battery systems without pre-regulation. |
| VOUT Range | 1.3V to 80V; supports wide-output applications including telecom -48V bus regulation and high-voltage LED drivers. |
| Switching Frequency | 100kHz to 400kHz; adjustable via RT resistor; allows optimization of size vs. efficiency and EMI performance. |
| Gate Drivers | Quad N-channel drivers (TG1/BG1/TG2/BG2); drives external high-side and low-side MOSFETs with 20ns rise/fall times and <100ns dead-time control. |
| LDO Output | 3.3V/12mA; powers external logic or sensors; requires ≥0.1µF ceramic bypass capacitor at LDO33 pin. |
| Operating Temp | –40°C to 125°C junction; qualified for industrial and extended-temperature embedded power systems. |
| Package | 38-lead Plastic TSSOP (FE package); exposes thermal pad (Pin 39 = GND); θJA = 25°C/W. |
Pinout & Package
LT8705AIFE#PBF uses a 38-lead plastic TSSOP (FE package) with exposed thermal pad (Pin 39) soldered to PCB ground. Pin numbering follows standard FE38(31) variation. Unlike the QFN variant, the TSSOP version omits SRVO_xxx and SWEN pins - these functions are not implemented.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SHDN (Pin 4) | Shutdown Control Input | Active-high enable; pulls quiescent current to ≤1µA when grounded; must not be left floating. |
| FBIN (Pin 8), FBOUT (Pin 9) | Voltage Feedback Inputs | Connect to resistor dividers for input/output voltage regulation; each referenced to internal 1.205V/1.207V precision bandgap. |
| IMON_IN (Pin 3), IMON_OUT (Pin 10) | Current Monitor Outputs | Sink current proportional to sensed input/output current; full-scale output = 100µA at 1.208V reference. |
| CSPIN/CSNIN (Pins 37/36), CSPOUT/CSNOUT (Pins 34/32) | Current Sense Inputs | Differential inputs for external sense resistors RSENSE1 (input) and RSENSE2 (output); common-mode range up to 80V. |
| TG1/BG1/TG2/BG2 (Pins 26/17/21/19) | MOSFET Gate Drivers | Drive external N-MOSFETs in 4-switch buck-boost topology; BGx referenced to GND, TGx referenced to SWx nodes. |
| INTVCC (Pin 1), GATEVCC (Pin 18) | Internal Power Rails | 6.35V regulated supply; GATEVCC must be tied directly to INTVCC; bypass with ≥4.7µF ceramic capacitor. |
| VIN (Pin 38), EXTVCC (Pin 30) | Main & Auxiliary Supplies | VIN powers IC when EXTVCC < 6.22V; EXTVCC > 6.4V switches internal regulator source - reduces VIN load. |
| MODE (Pin 2), RT (Pin 15), SS (Pin 12) | Configuration & Timing | MODE selects FCM/Burst/DCM; RT sets oscillator frequency; SS controls soft-start ramp time via external capacitor. |
Key Features
| Feature | Design Value |
|---|---|
| Single-inductor buck-boost topology | Eliminates need for separate buck and boost stages; supports VIN above, below, or equal to VOUT in one converter stage. |
| Four independent regulation loops | Simultaneous input voltage, output voltage, input current, and output current control - essential for MPPT and battery charge management. |
| Integrated 3.3V LDO | Provides local bias for external circuitry without requiring auxiliary supply; rated for 12mA load with ±1% regulation. |
| Synchronizable fixed-frequency operation | Enables multi-phase or noise-sensitive system timing alignment via SYNC pin; supports external clock frequencies from 100kHz to 400kHz. |
| Thermal-aware CLKOUT | CLKOUT duty cycle varies linearly with die temperature - usable as a non-invasive junction temperature monitor without external sensor. |
Applications
| Solar Charge Controller | Telecom Voltage Stabilizer |
|---|---|
Use Scenario: Regulating variable PV array output (36–80V) to charge 48V battery bank while limiting input current during partial shading. IC Role / Device Role / Timing Role: Primary buck-boost controller managing dual-loop MPPT (via FBIN + IMON_IN) and constant-current/constant-voltage battery charging (via FBOUT + IMON_OUT). Use Value: Enables >95% conversion efficiency across wide input range; eliminates need for separate DC-DC stages or external current-sense amplifiers. | Use Scenario: Stabilizing fluctuating -48V telecom rectifier output under varying load and line conditions. IC Role / Device Role / Timing Role: High-voltage buck-boost regulator maintaining precise -48V output using FBOUT feedback and input overvoltage protection (via FBIN monitoring). Use Value: Supports 80V absolute max input rating; withstands telecom surge transients; integrated UVLO prevents latch-up during brownouts. |
| Automotive 12V/24V System Regulator | Battery Backup Power Supply |
Use Scenario: Providing stable 5V/3.3V rail from vehicle battery (6–16V cold-crank to 36V load-dump) with reverse-polarity and overvoltage protection. IC Role / Device Role / Timing Role: Input-robust buck-boost controller using FBIN for input supervision and MODE pin for light-load efficiency optimization. Use Value: Operates down to 2.8V VIN - supports start-stop systems; 125°C junction rating ensures reliability under hood temperatures. | Use Scenario: Seamless switchover between AC adapter (12–24V) and Li-ion battery (3.0–4.2V/cell) to maintain uninterrupted 5V USB power. IC Role / Device Role / Timing Role: Dual-input buck-boost controller regulating output from either source using FBIN/FBOUT loop coordination and IMON_IN monitoring for source priority. Use Value: Single-chip solution replaces discrete OR-ing + regulation; programmable current limits prevent battery over-discharge. |
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; identical pinout except no IMON_IN/IMON_OUT; lacks input/output current regulation loops. | Suitable for voltage-only regulation; not viable for MPPT or current-limited designs requiring dual-loop control. | Select LT8705AIFE#PBF when input/output current monitoring or coordinated voltage/current regulation is required. |
| LT8708IUHF#PBF | QFN-38 package; adds SRVO_xxx status pins and SWEN; supports same voltage/current loops but different thermal profile (θJA = 34°C/W). | Preferred for space-constrained layouts needing status signaling; unsuitable where TSSOP footprint or lower θJA is mandatory. | Choose LT8705AIFE#PBF for TSSOP-compatible industrial boards with established layout; choose LT8708 for compact, thermally managed designs with status visibility. |
Compared with LTC3780EFE#PBF, LT8705AIFE#PBF adds full four-loop regulation and current monitoring capability; compared with LT8708IUHF#PBF, it trades QFN-specific features for TSSOP mechanical compatibility and improved thermal resistance in board-level assembly.
Availability
LT8705AIFE#PBF is available at Aetrix Electronics and suitable for solar energy systems, telecom infrastructure, and automotive power modules requiring stable component supply, long-term lifecycle support, and industrial-grade temperature performance.
Supply support for LT8705AIFE#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 product lines with rigorous qualification standards.
The LT8705A series belongs to Linear's high-voltage buck-boost controller family, designed specifically for demanding applications requiring wide VIN/VOUT ranges, multi-loop regulation, and robust operation in harsh environments.
FAQ
What is the maximum input voltage rating for the LT8705AIFE#PBF?
The LT8705AIFE#PBF has an absolute maximum input voltage rating of 80V on the VIN and EXTVCC pins. This allows direct connection to 48V and 72V battery systems, solar arrays, and telecom rectifiers without external clamping. Operation beyond this limit risks permanent damage per Absolute Maximum Ratings.
Does the LT8705AIFE#PBF support synchronous rectification?
Yes, the LT8705AIFE#PBF supports synchronous rectification through its quad N-channel gate drivers (TG1/BG1/TG2/BG2). These drivers enable full synchronous operation in both buck and boost phases, achieving up to 98% efficiency. External high-side and low-side MOSFETs must be selected to match the driver voltage swing and timing requirements.
Can the LT8705AIFE#PBF operate with input voltage below 2.8V?
No, the LT8705AIFE#PBF requires a minimum VIN of 2.8V when EXTVCC = 0V, or 5.5V when EXTVCC ≥ 7.5V. Below these thresholds, the internal regulators cannot sustain bias, and the device will not start or may reset. For sub-2.8V applications, consider alternative controllers like the LT3999 or discrete solutions.
How does the MODE pin affect efficiency in light-load conditions?
The MODE pin configures light-load behavior: <0.4V enables forced continuous mode (FCM), 1.0–1.7V enables Burst Mode® (reducing quiescent current to ~2.65mA), and >2.3V enables discontinuous conduction mode (DCM). Burst Mode® maximizes light-load efficiency at the expense of increased output ripple; FCM maintains low ripple but higher standby loss.
Is the LT8705AIFE#PBF pin-compatible with the LT8705A QFN variants?
No, the LT8705AIFE#PBF (TSSOP) is not pin-compatible with QFN variants like LT8705AEUHF#PBF. Key differences include missing SRVO_FBIN/SRVO_IIN/SRVO_IOUT/SRVO_FBOUT and SWEN pins in the TSSOP package, and relocated GND (Pin 1) and IMON_IN (Pin 3). PCB layout must be redesigned for package interchange.
LT8705AIFE#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
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 38-TSSOP-EP
LT8705AIFE#PBF FAQ
1.How can I place an order for LT8705AIFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT8705AIFE#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 LT8705AIFE#PBF reliable?
The price and inventory of LT8705AIFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT8705AIFE#PBF is usually 5 days.
3.What payment methods are accepted for LT8705AIFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT8705AIFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT8705AIFE#PBF?
LT8705AIFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT8705AIFE#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 LT8705AIFE#PBF?
For technical support, including LT8705AIFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT8705AIFE#PBF requirements.
6.How does Aetrix verify that LT8705AIFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT8705AIFE#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 LT8705AIFE#PBF meets industry standards.
7.What is the process for return or replacement of LT8705AIFE#PBF?
All LT8705AIFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT8705AIFE#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 LT8705AIFE#PBF part is unused and in its original packaging.
Return procedure for LT8705AIFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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