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Analog Devices Inc. LT8705IUHF#PBF
- Part No.:
- LT8705IUHF#PBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 38-WFQFN Exposed Pad
- Datasheet:
-
LT8705IUHF#PBF.pdf
- Description:
- IC REG CTRLR BUCK-BOOST 38QFN
- Quantity:
- Payment:
- Shipping:
Inventory:2,992
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Product details
Overview
LT8705IUHF#PBF 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 industrial and automotive power systems. It supports 2.8V–80V input and 1.3V–80V output, integrates quad N-channel gate drivers, and delivers up to 98% efficiency in synchronous rectification mode. Its primary circuit role is regulating output voltage across buck, boost, and buck-boost regions using a single inductor.
For engineers reviewing the LT8705IUHF#PBF datasheet, LT8705IUHF#PBF pinout, LT8705IUHF#PBF application, or LT8705IUHF#PBF equivalent, key selection considerations include its 38-lead QFN package with exposed thermal pad, integrated input/output current monitoring, servo feedback loop status indicators, and programmable operating frequency from 100kHz to 400kHz via RT resistor.
Technical Context
The LT8705IUHF#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 diode-ANDed at the VC error amplifier output. Its topology enables seamless transition between buck, boost, and buck-boost modes without external mode switching logic.
It features integrated gate drivers for two high-side (TG1/TG2) and two low-side (BG1/BG2) N-MOSFETs, with precise timing control including minimum on/off times (260–265ns) and dead-time management. The controller supports Burst Mode® operation, discontinuous conduction mode (DCM), and forced continuous conduction mode (CCM) selected via the MODE pin.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VIN Range | 2.8V to 80V - supports 12V, 24V, 48V, and 72V battery/solar/telecom inputs without pre-regulation |
| VOUT Range | 1.3V to 80V - enables stable output across buck (VIN > VOUT), boost (VIN < VOUT), and buck-boost (VIN ≈ VOUT) regions |
| Switching Frequency | 100kHz to 400kHz - adjustable via RT resistor; synchronizable to external clock via SYNC pin |
| Efficiency | Up to 98% - achieved via synchronous rectification and low-loss gate drive architecture |
| Gate Drivers | Quad N-channel drivers (TG1/BG1/TG2/BG2) - supports discrete external MOSFETs with fast rise/fall times (20ns) |
| Current Monitoring | Input and output current sense with programmable thresholds - enables overcurrent protection and power limiting |
| Package | 38-lead (5mm × 7mm) QFN with exposed thermal pad - optimized for high-voltage isolation and thermal dissipation |
| Operating Temp | –40°C to +125°C junction - qualified for automotive under-hood and industrial ambient environments |
Pinout & Package
LT8705IUHF#PBF is housed in a 38-lead plastic QFN package (5mm × 7mm) with an exposed GND pad (Pin 39) requiring PCB soldering for thermal and electrical integrity. Pin functions are validated per Linear Technology's official datasheet Rev. D (2016).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| SHDN (Pin 1) | Shutdown Control | Active-low enable; pulls quiescent current to ≤1µA when grounded |
| CSP/CSN (Pins 2–3) | Inductor Current Sense Input | Differential input for main current sensing; sets peak current limit via VC and RSENSE |
| LDO33 (Pin 4) | 3.3V Regulator Output | Provides 12mA regulated supply for external logic or biasing; requires ≥0.1µF ceramic bypass |
| FBIN/FBOUT (Pins 5–6) | Voltage Feedback Inputs | Resistor-divider interfaces for input (FBIN) and output (FBOUT) regulation loops |
| IMON_OUT/IMON_IN (Pins 7, 38) | Current Monitor Outputs | Current-source outputs proportional to output/input current; used for monitoring or limiting |
| VC (Pin 8) | Error Amplifier Output | Diode-AND node of EA1–EA4; connects to external compensation network |
| CLKOUT (Pin 10) | Temperature-Monitored Clock | Outputs oscillator signal with duty cycle linearly tracking die temperature (22.7–77%) |
| SYNC (Pin 11) | Frequency Synchronization | Accepts external clock (1.3V high / 0.5V low); overrides internal oscillator |
| RT (Pin 12) | Frequency Set Resistor | Connects to GND; sets free-running frequency (e.g., 215kΩ → 202kHz) |
| TG1/BG1/TG2/BG2 (Pins 14, 16, 18, 22) | N-MOSFET Gate Drivers | Drive top/bottom switches with 20ns rise/fall; support bootstrap operation |
| BOOST1/BOOST2 (Pins 17, 23) | Floating Driver Supplies | Connect to bootstrap capacitors; swing up to VIN+GATEVCC and VOUT+GATEVCC |
| SW1/SW2 (Pins 19, 21) | Switch Node Terminals | Connect to source terminals of M2/M3 (buck) and M1/M4 (boost); rated to 81V |
| SRVO_FBIN/SRVO_FBOUT (Pins 25, 28) | Feedback Loop Status | Open-drain outputs indicating active input/output voltage regulation loops |
| SRVO_IIN/SRVO_IOUT (Pins 26–27) | Current Loop Status | Open-drain outputs signaling activation of input/output current regulation |
| EXTVCC (Pin 29) | External Bias Supply | Enables INTVCC sourcing from external 6.4V+ supply, reducing VIN load |
| CSPOUT/CSNOUT (Pins 31–30) | Output Current Sense | Differential input for secondary current sensing (RSENSE2) at output |
| CSPIN/CSNIN (Pins 33–32) | Input Current Sense | Differential input for primary current sensing (RSENSE1) at input |
| VIN (Pin 34) | Main Power Input | Primary high-voltage input rail; requires local ≥4.7µF ceramic bypass |
| INTVCC (Pin 35) | Internal 6.35V Regulator | Supplies gate drivers and internal circuitry; must connect to GATEVCC |
| SWEN (Pin 36) | Switch Enable | Active-high control for enabling/disabling PWM switching (QFN only) |
| MODE (Pin 37) | Operating Mode Select | Voltage-selectable: <0.4V = CCM, 1.0–1.7V = Burst Mode®, >2.3V = DCM |
| GND (Pins 13, 39) | Ground Reference | Power and signal ground; exposed pad (Pin 39) must be soldered to PCB ground plane |
Key Features
| Feature | Design Value |
|---|---|
| Synchronous 4-switch topology | Enables single-inductor buck-boost conversion with bidirectional energy flow and no external mode control logic |
| Four independent feedback loops | Allows simultaneous regulation of input voltage, output voltage, input current, and output current for complex power management |
| Integrated 3.3V/12mA LDO | Reduces BOM count by powering external monitoring ICs or level-shifters without auxiliary regulators |
| Programmable frequency & synchronization | Supports EMI reduction via spread-spectrum-compatible sync and avoids beat frequencies in multi-rail systems |
| Servo status pins (SRVO_xxx) | Provides real-time visibility into active regulation loops-critical for fault diagnostics and adaptive control algorithms |
| High-voltage QFN package | 38-lead 5×7mm QFN with enhanced creepage/clearance meets reinforced insulation requirements for 80V systems |
Applications
| Solar Charge Controller | Automotive DC-DC Converter |
|---|---|
Use Scenario: Regulating variable PV array output (30–80V) to charge 48V battery banks while limiting input current during partial shading. IC Role / Device Role / Timing Role: Buck-boost controller managing bidirectional power flow, enforcing MPPT input current limits and constant-voltage battery charging. Use Value: Single-inductor architecture reduces component count and cost vs. cascaded buck+boost; 98% efficiency minimizes thermal stress in sealed enclosures. | Use Scenario: Converting unstable vehicle battery voltage (6–16V) to stable 12V or 5V rails for infotainment, ADAS sensors, and telematics modules. IC Role / Device Role / Timing Role: Wide-input buck-boost regulator maintaining regulated output during cold-crank (6V) and load-dump (16V) transients. Use Value: 2.8V start-up capability ensures operation during deep battery discharge; integrated current monitoring enables smart load shedding. |
| Telecom Voltage Stabilizer | Industrial 48V Power System |
Use Scenario: Stabilizing –48V telecom distribution bus against line drops and surges while delivering clean +48V or +12V outputs to line cards. IC Role / Device Role / Timing Role: High-efficiency buck-boost controller providing isolated or non-isolated regulated outputs with precise current limiting. Use Value: 80V absolute maximum rating accommodates telecom surge standards (IEC 61000-4-5); CLKOUT-based thermal monitoring prevents derating in dense chassis. | Use Scenario: Powering PLC I/O modules, motor drives, and fieldbus interfaces from unregulated 48V industrial bus with tight output tolerance and overcurrent protection. IC Role / Device Role / Timing Role: Primary DC-DC controller implementing programmable current limits and output voltage sequencing via FBOUT/VC loop control. Use Value: Dual current monitor outputs (IMON_IN/IMON_OUT) feed safety-critical watchdog circuits; QFN package supports conformal coating for harsh environments. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar buck-boost controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT8708IUHF#PBF | Higher 150°C max junction temperature; identical pinout and feature set; adds dual-phase interleaving capability | Required for extended-temperature industrial or under-hood automotive use where 125°C is insufficient | Select LT8708IUHF#PBF when operating ambient exceeds 105°C or interleaved operation is needed for lower ripple |
| MPQ4332GJ-AEC1-P | Monolithic 3.5A buck-boost converter (integrated MOSFETs); narrower 4–36V input; fixed 500kHz frequency | Suitable for space-constrained, lower-power (<50W) applications where external FETs are undesirable | Choose MPQ4332GJ-AEC1-P for compact, cost-sensitive designs needing <3.5A output without external power stage design |
Compared with LT8705IUHF#PBF, the LT8708IUHF#PBF extends thermal capability and adds phase control, while the MPQ4332GJ-AEC1-P trades flexibility for integration and size-making LT8705IUHF#PBF optimal for high-power, high-voltage, and thermally demanding discrete-FET designs.
Availability
LT8705IUHF#PBF is available at Aetrix Electronics and suitable for solar charge controllers, automotive DC-DC converters, and telecom voltage stabilizers requiring stable component supply across extended temperature ranges and long production lifecycles.
Supply support for LT8705IUHF#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 full product support, documentation, and manufacturing continuity for the LT8705 series.
The LT8705 product line targets high-voltage, wide-range DC-DC conversion in automotive, industrial, and renewable energy systems-designed specifically for reliability under extreme input transients and thermal stress.
FAQ
What is the maximum input voltage supported by the LT8705IUHF#PBF?
The LT8705IUHF#PBF supports an absolute maximum input voltage of 80V on the VIN pin, with operational input range from 2.8V to 80V. This allows direct interface with 48V and 72V battery systems, solar arrays, and telecom power buses without external pre-regulation. The 80V rating is validated per Absolute Maximum Ratings table and applies across the full –40°C to +125°C junction temperature range.
Does the LT8705IUHF#PBF integrate MOSFETs or require external power switches?
The LT8705IUHF#PBF is a controller IC-not a monolithic converter-and requires four external N-channel MOSFETs (two high-side, two low-side). It provides integrated gate drivers (TG1/BG1/TG2/BG2) with 20ns rise/fall times and bootstrap support, but does not include power FETs. This architecture enables optimization for voltage, current, and thermal requirements beyond what monolithic solutions offer.
How does the LT8705IUHF#PBF handle mode transitions between buck, boost, and buck-boost operation?
The LT8705IUHF#PBF uses a proprietary current-mode control architecture that automatically and seamlessly transitions between buck, boost, and buck-boost regions based on input/output voltage relationship and load conditions-no external mode selection or control logic is required. The VC pin voltage dynamically adjusts to maintain regulation, and servo pins (SRVO_FBIN, SRVO_FBOUT, etc.) indicate which feedback loop is dominant in real time.
Can the LT8705IUHF#PBF be synchronized to an external clock, and what are the voltage thresholds?
Yes, the LT8705IUHF#PBF supports external synchronization via the SYNC pin. A valid sync clock must meet: high-level threshold ≥1.3V (min), low-level threshold ≤0.5V (max), and duty cycle between 20% and 80%. When driven below 0.5V, the device reverts to its internal free-running oscillator. This capability enables EMI reduction and coordinated switching in multi-rail power systems.
What is the purpose of the CLKOUT pin on the LT8705IUHF#PBF, and how is it used?
The CLKOUT pin on the LT8705IUHF#PBF serves dual purposes: (1) as a synchronized clock output toggling at the same frequency as the internal oscillator (or SYNC input), phase-shifted ~180°, and (2) as a die temperature monitor-the CLKOUT duty cycle varies linearly from 22.7% at –40°C to 77% at +125°C. It can drive capacitive loads up to 200pF and requires no external components for basic use.
LT8705IUHF#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 38-WFQFN 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-QFN (5x7)
LT8705IUHF#PBF FAQ
1.How can I place an order for LT8705IUHF#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT8705IUHF#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 LT8705IUHF#PBF reliable?
The price and inventory of LT8705IUHF#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT8705IUHF#PBF is usually 5 days.
3.What payment methods are accepted for LT8705IUHF#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT8705IUHF#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT8705IUHF#PBF?
LT8705IUHF#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT8705IUHF#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 LT8705IUHF#PBF?
For technical support, including LT8705IUHF#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT8705IUHF#PBF requirements.
6.How does Aetrix verify that LT8705IUHF#PBF is sourced from the original manufacturer or authorized distributors?
All LT8705IUHF#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 LT8705IUHF#PBF meets industry standards.
7.What is the process for return or replacement of LT8705IUHF#PBF?
All LT8705IUHF#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT8705IUHF#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 LT8705IUHF#PBF part is unused and in its original packaging.
Return procedure for LT8705IUHF#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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