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Analog Devices Inc. LT8705AMPFE#PBF
- Part No.:
- LT8705AMPFE#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 38-TFSOP (0.173", 4.40mm Width) 31 Leads, Exposed Pad
- Datasheet:
-
LT8705AMPFE#PBF.pdf
- Description:
- IC REG CTRLR BUCK-BOOST 38TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:3,058
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Product details
Overview
LT8705AMPFE#PBF from Analog Devices (formerly Linear Technology) is a high-performance synchronous 4-switch buck-boost DC/DC controller IC designed for wide-input, wide-output voltage regulation in harsh environments. It supports 2.8V–80V input and 1.3V–80V output, integrates quad N-channel gate drivers, and delivers up to 98% efficiency with synchronous rectification. It is used in high-reliability automotive and industrial power systems requiring operation across –55°C to +150°C junction temperature.
For engineers reviewing the LT8705AMPFE#PBF datasheet, LT8705AMPFE#PBF pinout, LT8705AMPFE#PBF application, or LT8705AMPFE#PBF equivalent, key selection criteria include its extended temperature grade (–55°C to 150°C), integrated input/output current/voltage feedback loops, MODE-selectable light-load operation (Burst/DCM/FCM), and compatibility with solar, telecom, and battery-powered HV systems where VIN may be above, below, or equal to VOUT.
Technical Context
The LT8705AMPFE#PBF implements a proprietary current-mode control architecture with four independent feedback loops-input voltage (FBIN), output voltage (FBOUT), input current (IMON_IN), and output current (IMON_OUT)-each tied to dedicated error amplifiers (EA3, EA4, EA2, EA1) with confirmed gain and transconductance values. Its 4-switch topology enables seamless buck-boost transitions without intermediate conversion stages.
It features synchronized fixed-frequency operation (100–400 kHz via RT resistor), onboard 6.35V INTVCC regulator and 3.3V/12mA LDO, plus open-drain SRVO pins (QFN-only; not present in FE package) for loop activity monitoring. The FE38 TSSOP package excludes SRVO_FBIN, SRVO_FBOUT, SRVO_IIN, SRVO_IOUT, and SWEN pins per datasheet Note 5.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VIN Range | 2.8V to 80V - supports direct connection to 24V/48V/72V battery banks, telecom -48V systems, and unregulated solar arrays without pre-regulation. |
| VOUT Range | 1.3V to 80V - enables single-stage generation of logic rails, analog supplies, or HV bias from variable inputs. |
| Operating Junction Temp | –55°C to +150°C - qualified for military, aerospace, and under-hood automotive applications with full parameter guarantee. |
| Switching Frequency | 100 kHz to 400 kHz - adjustable via RT pin; allows optimization of magnetics size vs. 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 controlled dead-time delays. |
| Integrated Regulators | 6.35V INTVCC (90–165mA) and 3.3V/12mA LDO - powers internal circuitry and provides auxiliary bias without external regulators. |
| Feedback Loops | Input voltage, output voltage, input current, output current - enables precise source/sink current limiting and input/output regulation in bidirectional or battery-charging topologies. |
Pinout & Package
LT8705AMPFE#PBF uses a 38-lead plastic TSSOP (FE38) package with exposed pad (Pin 39 = GND). Pin count and function mapping match the LT8705A FE package variant; SRVO and SWEN pins are omitted per datasheet Note 5.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SHDN (Pin 4) | Shutdown Control | Active-high enable; pulls quiescent current to ≤1µA when grounded - critical for low-power standby modes. |
| FBIN (Pin 8), FBOUT (Pin 9) | Voltage Feedback Inputs | High-impedance (≤10nA bias) inputs for resistor-divider networks; regulate VIN and VOUT independently with 1.205V/1.207V reference voltages. |
| IMON_IN (Pin 3), IMON_OUT (Pin 10) | Current Monitor Outputs | Current-source outputs proportional to sensed input/output current; 100µA max, 1.208V regulation point - interface directly to ADCs or comparator thresholds. |
| VC (Pin 11) | Error Amplifier Output | Compensation node for all four control loops; connects external RC network to set loop bandwidth and phase margin. |
| RT (Pin 15) | Oscillator Timing | Resistor-to-ground sets switching frequency (e.g., 215kΩ → 202kHz); enables precise EMI shaping and multi-phase synchronization. |
| TG1/BG1/TG2/BG2 (Pins 26/17/21/19) | MOSFET Gate Drivers | Drive external N-MOSFETs; TGx swing referenced to SWx nodes, BGx referenced to GND - enables full 4-switch synchronous operation. |
| VIN (Pin 38), EXTVCC (Pin 30) | Power Inputs | VIN supplies core logic; EXTVCC >6.4V powers INTVCC preferentially - improves efficiency and thermal performance in high-VIN applications. |
| GATEVCC (Pin 18), INTVCC (Pin 1) | Internal Supplies | GATEVCC must tie to INTVCC; INTVCC is regulated 6.35V output - eliminates need for external gate driver bias supplies. |
Key Features
| Feature | Design Value |
|---|---|
| Synchronous 4-switch topology | Enables single-inductor buck-boost conversion with VIN above, below, or equal to VOUT - eliminates need for separate buck + boost stages or transformer-based solutions. |
| Four independent feedback loops | Allows simultaneous regulation of input voltage, output voltage, input current, and output current - essential for battery charging, MPPT, and programmable power supply designs. |
| MODE-selectable light-load operation | Supports Burst Mode®, discontinuous conduction mode (DCM), or forced continuous conduction mode (FCM) - optimizes efficiency across 1000:1 load range without external circuitry. |
| –55°C to +150°C guaranteed operation | Full electrical specification compliance over extended temperature range - validated for mission-critical aerospace, defense, and industrial control applications. |
| Integrated 3.3V/12mA LDO | Provides clean, low-noise auxiliary supply for sensors, ADC references, or level-shifters - reduces BOM count and layout complexity. |
Applications
| Automotive Start-Stop Systems | Solar Charge Controllers |
|---|---|
Use Scenario: Regulating 12V/24V battery rail during engine cranking events where input dips to 3.5V while maintaining stable 5V/3.3V MCU supply. IC Role / Device Role / Timing Role: Buck-boost controller managing bidirectional energy flow between battery and loads; maintains VOUT despite VIN collapse or surge. Use Value: Prevents system reset during cold-crank by sustaining regulated output down to 2.8V VIN - enabled by wide input range and fast transient response. | Use Scenario: Converting variable PV array output (20–80V) to fixed 48V battery charge voltage with MPPT tracking and input current limiting. IC Role / Device Role / Timing Role: Primary DC/DC controller implementing input-voltage and input-current regulation loops for real-time MPPT execution. Use Value: Integrated IMON_IN and FBIN loops allow closed-loop MPPT without external op-amps or microcontroller intervention - reducing latency and component count. |
| Industrial Telecom Power | High-Voltage Test Equipment |
Use Scenario: Stabilizing –48V telecom distribution bus against load transients while delivering isolated ±15V analog supplies. IC Role / Device Role / Timing Role: High-efficiency buck-boost front-end regulating –48V input to generate intermediate 12V rail for downstream isolated DC/DC converters. Use Value: 98% peak efficiency and 100–400kHz frequency adjustability minimize heat sink size and meet stringent EMI Class B limits in dense telecom chassis. | Use Scenario: Generating programmable 0–80V output from 24V DC input for semiconductor parametric testing with precise current limiting. IC Role / Device Role / Timing Role: Precision-controlled HV source using FBOUT and IMON_OUT feedback loops to enforce voltage and current compliance simultaneously. Use Value: Dual-loop regulation ensures safe device-under-test protection - e.g., clamping output at 5A when VOUT reaches 80V, preventing DUT damage. |
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 4-switch architecture but rated only to 125°C; lacks IMON_IN/IMON_OUT current monitor outputs; no SRVO pins (FE package). | Not qualified for –55°C operation or sustained 150°C ambient; unsuitable for aerospace or under-hood use. | Select LT8705AMPFE#PBF when extended temperature range and dual current monitoring are required. |
| MP2918GL-Z | Monolithic 4-switch buck-boost IC (integrated MOSFETs); max 36V input; no input current sensing; fixed 300kHz frequency. | Lower voltage rating and no programmable frequency limit use in HV solar or telecom; integrated FETs reduce solution size but limit power scalability. | Choose LT8705AMPFE#PBF for >36V input, field-replaceable FETs, or design flexibility with external MOSFET selection. |
Compared with LTC3780EFE#PBF and MP2918GL-Z, the LT8705AMPFE#PBF uniquely combines –55°C to +150°C guaranteed operation, full four-loop regulation (FBIN/FBOUT/IMON_IN/IMON_OUT), and 2.8V–80V input capability - making it the only option qualified for high-reliability, wide-range, high-temperature buck-boost control.
Availability
LT8705AMPFE#PBF is available at Aetrix Electronics and suitable for automotive start-stop systems, solar charge controllers, and industrial telecom power supplies requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT8705AMPFE#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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors.
The LT8705A product line was engineered specifically for high-voltage, wide-range DC/DC conversion in mission-critical applications - emphasizing reliability, precision regulation, and extended temperature operation in automotive, industrial, and renewable energy systems.
FAQ
What is the guaranteed operating temperature range for LT8705AMPFE#PBF?
The LT8705AMPFE#PBF is fully specified and guaranteed over a junction temperature range of –55°C to +150°C. This extended grade is validated per datasheet specifications and distinguishes it from commercial-grade variants (e.g., LT8705AEUHF#PBF, rated –40°C to +125°C). Its qualification makes LT8705AMPFE#PBF suitable for aerospace, defense, and under-hood automotive applications where extreme thermal environments exist.
Does LT8705AMPFE#PBF support input voltage regulation and output current limiting simultaneously?
Yes, the LT8705AMPFE#PBF supports concurrent input voltage (FBIN), output voltage (FBOUT), input current (IMON_IN), and output current (IMON_OUT) regulation via four independent feedback loops. Each loop uses a dedicated error amplifier (EA3, EA4, EA2, EA1) with confirmed transconductance and voltage gain. This enables true multi-parameter control - for example, maintaining constant VOUT while enforcing a hard IMON_OUT current limit during overload conditions.
What package type and pin count does LT8705AMPFE#PBF use?
LT8705AMPFE#PBF uses a 38-lead plastic TSSOP package (FE38 variation), with an exposed thermal pad (Pin 39) that must be soldered to the PCB ground plane. It shares pinout compatibility with other LT8705A FE variants (e.g., LT8705AHFE#PBF), but omits SRVO_FBIN, SRVO_FBOUT, SRVO_IIN, SRVO_IOUT, and SWEN pins per datasheet Note 5 - confirming these functions are unavailable in the TSSOP configuration.
How is switching frequency set on LT8705AMPFE#PBF?
Switching frequency on LT8705AMPFE#PBF is set by an external resistor connected from the RT pin (Pin 15) to ground. The free-running frequency ranges from 100 kHz to 400 kHz depending on RT value - for example, 215kΩ yields 202kHz (typical). The SYNC pin (Pin 14) allows external clock synchronization, and CLKOUT (Pin 13) provides a 180° out-of-phase clock signal for multi-phase interleaving or die temperature monitoring.
Can LT8705AMPFE#PBF operate with input voltage lower than 6.4V?
Yes, LT8705AMPFE#PBF operates with VIN as low as 2.8V, but requires EXTVCC ≥ 6.4V (typical) to power the INTVCC regulator. When EXTVCC is below 6.22V (typical), INTVCC is powered from VIN. At VIN < 6.4V, the part remains functional provided VIN stays within 2.8V–80V and sufficient current is supplied to sustain INTVCC and gate drivers - verified in datasheet Electrical Characteristics under "VIN Operating Voltage Range" with EXTVCC = 0V.
LT8705AMPFE#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:
- -55°C ~ 125°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 38-TSSOP-EP
LT8705AMPFE#PBF FAQ
1.How can I place an order for LT8705AMPFE#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT8705AMPFE#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 LT8705AMPFE#PBF reliable?
The price and inventory of LT8705AMPFE#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT8705AMPFE#PBF is usually 5 days.
3.What payment methods are accepted for LT8705AMPFE#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT8705AMPFE#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT8705AMPFE#PBF?
LT8705AMPFE#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT8705AMPFE#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 LT8705AMPFE#PBF?
For technical support, including LT8705AMPFE#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT8705AMPFE#PBF requirements.
6.How does Aetrix verify that LT8705AMPFE#PBF is sourced from the original manufacturer or authorized distributors?
All LT8705AMPFE#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 LT8705AMPFE#PBF meets industry standards.
7.What is the process for return or replacement of LT8705AMPFE#PBF?
All LT8705AMPFE#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT8705AMPFE#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 LT8705AMPFE#PBF part is unused and in its original packaging.
Return procedure for LT8705AMPFE#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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