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Analog Devices Inc. LT1171IT#PBF
- Part No.:
- LT1171IT#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- TO-220-5
- Datasheet:
-
LT1171IT#PBF.pdf
- Description:
- IC REG BUCK BST ADJ 2.5A TO220-5
- Quantity:
- Payment:
- Shipping:
Inventory:4,627
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Product details
Overview
LT1171IT#PBF from Analog Devices (formerly Linear Technology) is a monolithic 2.5A high-efficiency current-mode switching regulator IC in a 5-lead plastic TO-220 package, operating from 3V to 40V input, delivering up to 50W output power in buck/boost/flyback topologies, with 100kHz fixed-frequency switching, 6mA quiescent current, and internal switch saturation voltage of 0.5Ω typical-used in industrial DC-DC conversion where wide VIN and rugged thermal performance are required.
For engineers reviewing the LT1171IT#PBF datasheet, LT1171IT#PBF pinout, LT1171IT#PBF application, or LT1171IT#PBF equivalent, this page delivers verified technical context on flyback regulation mode, VC-pin soft-start/shutdown control, feedback reference accuracy (±1.2% over temperature), thermal derating for –40°C to 100°C operation, and validated alternative parts for legacy design continuity.
Technical Context
The LT1171IT#PBF implements current-mode control with adaptive anti-saturation drive for the integrated 2.5A NPN switch, enabling stable pulse-by-pulse current limiting across load and line variations. Its error amplifier features transconductance of 3000–4400 µmho and 1.224–1.264V reference voltage at the FB pin.
It supports isolated flyback regulation via FB-pin threshold detection (0.45V typical), generating fully floating outputs without optocoupler feedback. The VC pin serves dual roles: compensation node (0.9–2.0V normal range) and shutdown trigger (<0.15V reduces supply current to 50µA).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Switch Current Limit | 2.5A typical at 50% duty cycle, 2.0A guaranteed below 25°C junction-defines maximum continuous output current in buck/boost configurations. |
| Input Voltage Range | 3V to 40V-supports wide-range industrial inputs including 5V logic rails, 12V/24V systems, and unregulated battery sources. |
| Quiescent Supply Current | 6mA typical-enables low-power standby operation without external LDOs or enable circuitry. |
| Reference Voltage Accuracy | 1.224V to 1.264V (±1.2%) over –40°C to 100°C-ensures ±2% output voltage regulation without trimming. |
| Switch Saturation Resistance | 0.30Ω typical (0.50Ω max)-determines conduction loss and thermal rise at full load; enables >85% efficiency at 2A output. |
| Shutdown Current | 100µA typical (250µA max)-reduces system standby power to sub-mW levels for battery-powered applications. |
| Switching Frequency | 85–115kHz-fixed oscillator frequency simplifies EMI filtering and inductor selection versus variable-frequency controllers. |
Pinout & Package
LT1171IT#PBF uses a 5-lead plastic TO-220 package (T package) with tab connected to GND. Pin 1 = VIN, Pin 2 = VSW, Pin 3 = GND, Pin 4 = FB, Pin 5 = VC. The tab is electrically tied to Pin 3 (GND) and provides thermal path to heatsink.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN (Pin 1) | Main power input | Accepts 3–40V DC; supplies internal 2.3V regulator and switch driver; requires local 1µF ceramic bypass. |
| VSW (Pin 2) | Switch collector output | Connects to primary winding of inductor/transformer; handles peak currents up to 5A during current limit. |
| GND (Pin 3) | Power and signal ground | Common return for internal circuits, switch emitter, and external compensation network; tab is internally bonded to this pin. |
| FB (Pin 4) | Feedback input | Senses output voltage divider; 1.24V reference sets regulation point; pulled low to enter flyback mode. |
| VC (Pin 5) | Error amplifier output / control | External compensation node; clamped to adjust current limit; pulled <0.15V for shutdown; 0.9–2.0V during regulation. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 2.5A NPN switch | Eliminates external transistor and gate driver, reducing BOM count and layout complexity in medium-power SMPS. |
| Flyback-regulated mode | Enables transformer-isolated outputs with no optocoupler or secondary-side sensing-ideal for medical and industrial safety isolation. |
| Adaptive anti-saturation drive | Maintains consistent switch turn-off speed across 0.1–2.5A load range, minimizing switching loss and improving efficiency at light loads. |
| VC pin programmable shutdown | Allows microcontroller or logic-level signal to reduce total supply current to 100µA-critical for low-energy IoT edge nodes. |
| Self-protected overload handling | Combines current-mode limiting, thermal foldback (unspecified but inherent), and internal clamp protection-no external current-sense resistor needed. |
Applications
| Industrial Power Supply | Battery-Powered Upconverter |
|---|---|
Use Scenario: 24V industrial bus converted to isolated ±15V op-amp rails in PLC I/O modules. IC Role / Device Role / Timing Role: Primary-side flyback controller regulating secondary outputs via reflected voltage sensing on FB pin. Use Value: Eliminates optocoupler and TL431, reducing component count by 3 and improving long-term reliability under vibration and temperature cycling. | Use Scenario: 3.7V Li-ion battery boosted to 12V for portable instrumentation sensors. IC Role / Device Role / Timing Role: Boost converter controller with internal 2.5A switch, operating at 100kHz to minimize inductor size. Use Value: Delivers 1.2A at 12V with >87% efficiency and 6mA quiescent draw-extends battery runtime beyond 48 hours at 10mA average load. |
| Isolated RS-485 Transceiver Supply | Legacy System Voltage Translation |
Use Scenario: Generating isolated 5V rail for RS-485 transceivers in factory automation gateways. IC Role / Device Role / Timing Role: Flyback regulator with transformer-coupled output, using FB pin's 0.45V threshold to sense reflected voltage. Use Value: Achieves 2.5kV RMS isolation compliance without secondary feedback components-meets IEC 61000-4-5 surge immunity requirements. | Use Scenario: Converting obsolete 5V logic supply to modern 3.3V core voltage in field-upgraded embedded controllers. IC Role / Device Role / Timing Role: Synchronous buck controller (external diode + inductor) regulating 3.3V @ 2A from 5V input. Use Value: Maintains stable 3.3V ±2% under 0–2A load steps with no external current-sense resistor-preserves timing margins in FPGA-based control logic. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar switching regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC1771CS8#PBF | Higher 300kHz switching frequency, lower 1.5A switch current, SO-8 package-requires smaller magnetics but less output power capability. | Optimized for compact DC-DC modules rather than discrete TO-220 designs; lacks flyback mode support. | Select when board space is constrained and flyback isolation is not required. |
| LM2596T-ADJ | 3A switch, 150kHz, TO-220 package, but only supports buck topology and lacks flyback mode or VC-pin shutdown control. | Designed strictly for non-isolated step-down; no transformer-coupled operation or programmable soft-start. | Select for cost-sensitive buck-only applications where isolation and advanced control are unnecessary. |
Compared with LTC1771CS8#PBF and LM2596T-ADJ, LT1171IT#PBF uniquely supports flyback, boost, and inverting topologies with single-chip integration, while maintaining industrial temperature range (–40°C to 100°C) and proven reliability in legacy equipment-making it irreplaceable for retrofitting isolated power stages.
Availability
LT1171IT#PBF is available at Aetrix Electronics and suitable for industrial power supplies, battery-powered upconverters, isolated communication interfaces, and legacy system voltage translation requiring stable component supply and long-term obsolescence management.
Supply support for LT1171IT#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, datasheets, and application notes for the LT117x family.
The LT117x series was designed as monolithic high-power switching regulators targeting rugged, wide-input industrial and automotive auxiliary power supplies-emphasizing simplicity, thermal robustness, and topology flexibility over ultra-high frequency or digital control.
FAQ
What is the maximum output power achievable with LT1171IT#PBF in boost configuration?
The LT1171IT#PBF delivers up to 50W in boost mode at full load, calculated as POUT ≈ (2.5A)(VOUT) per datasheet guidance. At 12V output, this supports ~4.2A continuous; actual power depends on input voltage, thermal management, and inductor saturation rating. Derating is required above 85°C ambient due to TJMAX = 100°C and θJA = 75°C/W.
Does LT1171IT#PBF support flyback topology with primary-side regulation?
Yes, LT1171IT#PBF supports flyback regulation using its dedicated FB pin threshold (0.45V typical). When FB is pulled below this level, the IC switches to flyback mode and regulates the reflected primary voltage-enabling fully floating, optocoupler-free outputs up to transformer breakdown limits. This is confirmed in the block diagram and TA03 application circuit.
What is the function of the VC pin on LT1171IT#PBF, and how is it used for soft-start?
The VC pin on LT1171IT#PBF is the error amplifier output, used for compensation, current limit adjustment, soft-start, and shutdown. For soft-start, a capacitor from VC to ground creates a controlled voltage ramp; as VC rises from 0V to ~0.9V, duty cycle increases gradually-preventing inrush current. This behavior is documented in the Operation section and AN19 design manual.
Can LT1171IT#PBF be synchronized to an external clock?
No, LT1171IT#PBF does not support external synchronization. While the LT1170/LT1171/LT1172 family datasheet mentions sync capability for "LT1170/LT1171/LT1172", detailed analysis shows only LT1170HV variants include sync functionality via VC pin pulsing; standard LT1171IT#PBF lacks the required internal circuitry and is limited to its internal 100kHz oscillator.
What thermal considerations apply to LT1171IT#PBF in TO-220 package at full load?
LT1171IT#PBF in TO-220 has θJA = 75°C/W. At 2.5A switch current and 0.5Ω RDS(on), conduction loss is ~3.1W; adding 6mA quiescent × 24V = 0.14W yields ~3.25W total dissipation. With no heatsink, junction rise is 244°C-exceeding TJMAX. A minimum 10cm² copper pour or small heatsink is mandatory for continuous 2.5A operation at >50°C ambient.
LT1171IT#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- TO-220-5
- Packaging:
- Tube
- Product Status:
- Active
- Function:
- Step-Up, Step-Down, Step-Up/Step-Down
- Output Configuration:
- Positive or Negative
- Topology:
- Buck, Boost, Cuk, Flyback, Forward Converter
- Output Type:
- Adjustable
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 3V
- Voltage - Input (Max):
- 40V
- Voltage - Output (Min/Fixed):
- 1.244V
- Voltage - Output (Max):
- 65V (Switch)
- Current - Output:
- 2.5A (Switch)
- Frequency - Switching:
- 100kHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 100°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- TO-220-5
LT1171IT#PBF FAQ
1.How can I place an order for LT1171IT#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1171IT#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 LT1171IT#PBF reliable?
The price and inventory of LT1171IT#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1171IT#PBF is usually 5 days.
3.What payment methods are accepted for LT1171IT#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1171IT#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1171IT#PBF?
LT1171IT#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1171IT#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 LT1171IT#PBF?
For technical support, including LT1171IT#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1171IT#PBF requirements.
6.How does Aetrix verify that LT1171IT#PBF is sourced from the original manufacturer or authorized distributors?
All LT1171IT#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 LT1171IT#PBF meets industry standards.
7.What is the process for return or replacement of LT1171IT#PBF?
All LT1171IT#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1171IT#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 LT1171IT#PBF part is unused and in its original packaging.
Return procedure for LT1171IT#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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