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Analog Devices Inc. LT1171CQ#PBF
- Part No.:
- LT1171CQ#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- TO-263-6, D2PAK (5 Leads + Tab), TO-263BA
- Datasheet:
-
LT1171CQ#PBF.pdf
- Description:
- IC REG BUCK BST ADJ 2.5A DDPAK-5
- Quantity:
- Payment:
- Shipping:
Inventory:151
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Product details
Overview
LT1171CQ#PBF from Analog Devices (formerly Linear Technology) is a monolithic 2.5A high-efficiency current-mode switching regulator IC in a 5-lead DD (TO-220 variant) package. It operates from 3V to 60V input, integrates a 2.5A internal power switch with 0.3Ω typical on-resistance, delivers up to 50W output power, and supports buck, boost, flyback, inverting, and Cuk topologies - used in industrial DC/DC conversion where wide VIN and rugged topology flexibility are required.
For engineers reviewing the LT1171CQ#PBF datasheet, LT1171CQ#PBF pinout, LT1171CQ#PBF application, or LT1171CQ#PBF equivalent, key selection criteria include its 100kHz fixed-frequency operation, 6mA quiescent current, shutdown mode drawing only 50µA, adaptive anti-saturation switch drive, and flyback-regulated floating-output capability for isolated supplies.
Technical Context
The LT1171CQ#PBF implements current-mode control with a 100kHz oscillator, enabling fast line/load transient response and simplified loop compensation. Its internal 2.5A NPN power switch features adaptive anti-saturation drive to maintain efficiency across wide load ranges, and the VC pin serves dual roles as error amplifier output and shutdown control node.
It supports both normal regulation (via FB pin referenced to 1.24V internal bandgap) and flyback mode (activated by pulling FB below 0.54V), where it regulates flyback pulse amplitude relative to VIN - enabling fully floating outputs without optocouplers. The device includes built-in overcurrent protection, thermal foldback, and self-protection against overload conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Switch Current Rating | 2.5A continuous (guaranteed at 50% duty cycle, TJ ≥ 25°C); enables robust 12V@2A or 24V@1A DC/DC designs without external MOSFETs. |
| Input Voltage Range | 3V to 60V; supports direct connection to 12V/24V/48V industrial buses and battery systems without pre-regulation. |
| Quiescent Supply Current | 6mA typical; minimizes no-load power loss in always-on systems such as remote sensors or backup supplies. |
| Shutdown Current | 50µA typical; allows ultra-low-power standby in battery-powered applications like portable instrumentation. |
| Switch On-Resistance | 0.30Ω typical (max 0.50Ω); limits conduction loss to ≤1.875W at 2.5A, supporting thermally constrained layouts. |
| Reference Voltage | 1.244V ±20mV (over temp); provides stable feedback threshold for precise output voltage setting with standard resistor dividers. |
| Switching Frequency | 100kHz nominal (88–115kHz range); balances EMI, inductor size, and efficiency for cost-sensitive industrial converters. |
| Flyback Reference Voltage | 15.0V to 18.0V (IFB = 50µA); enables transformer-coupled isolated outputs with direct primary-side regulation. |
Pinout & Package
LT1171CQ#PBF uses a 5-lead DD (DIP-style TO-220 variant) package with exposed tab electrically connected to GND. Thermal resistance θJA is 75°C/W (with PCB copper), and maximum junction temperature is 100°C.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN | Power Input | Primary supply input (3V–60V); must be decoupled near pin with ≥1µF ceramic capacitor to suppress switching noise. |
| VSW | Switch Collector Output | High-current open-collector NPN switch output; connects to inductor/diode in boost/buck/flyback configurations. |
| GND | Ground Reference | Power and signal ground; tab is internally bonded to this pin - requires low-impedance PCB ground plane. |
| FB | Feedback Input | Compares output-derived voltage to 1.244V reference; pulled low (<0.54V) to activate flyback regulation mode. |
| VC | Error Amplifier Output / Control | Current-source output (gm ≈ 3000–4400 µmho); sets switch current limit, enables soft-start, and triggers shutdown when <0.15V. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 2.5A Power Switch | Eliminates external transistor and driver, reducing BOM count and layout complexity in medium-power SMPS. |
| Flyback-Regulated Mode | Enables transformer-isolated outputs with primary-side sensing - avoids optocoupler and secondary-side TL431 circuitry. |
| Adaptive Anti-Saturation Drive | Maintains high efficiency (>85%) across 10:1 load range by dynamically adjusting base drive to prevent NPN saturation. |
| External Shutdown via VC Pin | Pulling VC to <0.15V reduces total supply current to 50µA, enabling hardware-controlled sleep/wake in embedded systems. |
| Wide Topology Support | Validated operation in buck, boost, flyback, forward, inverting, and Cuk configurations - simplifies reuse across multiple power architectures. |
| Self-Protected Overload Handling | Internal current limiting and thermal foldback prevent damage during short-circuit or startup surge without external circuitry. |
Applications
| Industrial DC/DC Conversion | Battery-Powered Upconverter |
|---|---|
Use Scenario: Converting 24V rail to 12V/5V for PLC I/O modules in factory automation cabinets with limited airflow. IC Role / Device Role / Timing Role: Primary switching controller implementing synchronous buck topology with integrated power switch and current-mode regulation. Use Value: Eliminates need for external MOSFET drivers and gate resistors, reducing board area by >30% versus discrete controller + FET solutions. | Use Scenario: Boosting single-cell Li-ion (3.0–4.2V) to 5V USB power for portable test equipment. IC Role / Device Role / Timing Role: High-efficiency boost converter controller with 6mA quiescent current and 50µA shutdown mode. Use Value: Extends battery runtime by >25% compared to linear regulators while maintaining stable 5V output across full battery discharge curve. |
| Floating Isolated Power Supply | Programmable Negative Voltage Generator |
Use Scenario: Generating ±15V analog supply for op-amps in data acquisition front-ends requiring galvanic isolation from digital ground. IC Role / Device Role / Timing Role: Flyback-regulated controller using primary-side feedback to regulate isolated secondary winding voltage. Use Value: Achieves <±2% output regulation without optocoupler or secondary-side reference, reducing component count and cost by 40%. | Use Scenario: Creating adjustable –10V to –26V LCD contrast supply from 5V logic rail in medical display panels. IC Role / Device Role / Timing Role: Inverting topology controller with programmable FB divider and VC-based soft-start. Use Value: Enables precise negative voltage tuning via two external resistors, eliminating need for dedicated negative charge-pump ICs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar high-voltage switching regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT1170CQ#PBF | 5A switch rating (vs 2.5A), 0.15Ω RDS(on), higher max output power (100W), same pinout and package. | Suitable for higher-current designs (e.g., 12V@4A) but dissipates more heat at light loads due to larger die. | Select when >2.5A peak switch current is required; verify thermal margin with θJA = 75°C/W and PCB copper area. |
| LT1172CQ#PBF | 1.25A switch rating (half of LT1171), 0.60Ω RDS(on), lower max power (25W), identical pinout and package. | Better suited for low-power isolated supplies (e.g., [email protected]) where efficiency at light loads matters more than peak current. | Select for cost-sensitive, lower-power applications where 1.25A switch current suffices and smaller thermal footprint is preferred. |
Compared with LT1170CQ#PBF and LT1172CQ#PBF, the LT1171CQ#PBF offers optimal balance of current capability (2.5A), thermal performance (75°C/W), and system-level efficiency across 10–50W industrial DC/DC designs - making it the default choice when neither extreme current nor minimal power is required.
Availability
LT1171CQ#PBF is available at Aetrix Electronics and suitable for industrial automation, battery-powered instrumentation, isolated sensor interfaces, and programmable power supplies requiring stable component supply, long-term lifecycle support, and lead-free compliance.
Supply support for LT1171CQ#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 LT117x family.
The LT117x series was designed as monolithic high-power switching regulators targeting rugged, topology-flexible DC/DC conversion in industrial, automotive, and telecom infrastructure - emphasizing integration, fault resilience, and wide-input operation.
FAQ
What is the maximum input voltage supported by the LT1171CQ#PBF?
The LT1171CQ#PBF supports a maximum supply voltage of 60V under absolute maximum ratings. For continuous operation, the recommended maximum input is 40V per the standard grade specification. Exceeding 40V requires verification of switch breakdown margin (65V min) and thermal design, especially in high-duty-cycle topologies like buck or inverting.
Can the LT1171CQ#PBF be used in flyback topology with primary-side regulation?
Yes, the LT1171CQ#PBF supports flyback-regulated mode: pulling the FB pin below 0.54V disconnects the main error amplifier and activates the flyback amplifier, which regulates flyback pulse amplitude relative to VIN. This enables fully floating, optocoupler-free isolated outputs - confirmed in the datasheet's block diagram and Typical Applications section.
What is the purpose of the VC pin on the LT1171CQ#PBF?
The VC pin on the LT1171CQ#PBF serves four critical functions: (1) error amplifier output for loop compensation, (2) current limit adjustment via external clamping, (3) soft-start initiation using a capacitor, and (4) total shutdown activation when pulled below 0.15V. Its transconductance (3000–4400 µmho) directly controls switch current trip level.
Does the LT1171CQ#PBF require an external catch diode in boost configuration?
Yes, the LT1171CQ#PBF requires an external catch diode in boost topology. As a monolithic NPN switch, it lacks a built-in body diode. A fast-recovery or Schottky diode (e.g., MBR330) must be placed between VSW and output to provide the freewheeling path during switch off-time - explicitly shown in all boost application schematics in the datasheet.
How does the LT1171CQ#PBF handle overcurrent or short-circuit conditions?
The LT1171CQ#PBF provides pulse-by-pulse current limiting: switch conduction terminates when sensed current reaches the programmed limit (2.5A typical at 50% duty cycle). It also includes thermal foldback - reducing current limit as junction temperature rises - and self-protection that prevents latch-up or destruction during sustained overload, as verified in the "Self-Protected Against Overloads" feature list.
LT1171CQ#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- TO-263-6, D2PAK (5 Leads + Tab), TO-263BA
- 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:
- 0°C ~ 100°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- DDPAK-5
LT1171CQ#PBF FAQ
1.How can I place an order for LT1171CQ#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1171CQ#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 LT1171CQ#PBF reliable?
The price and inventory of LT1171CQ#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1171CQ#PBF is usually 5 days.
3.What payment methods are accepted for LT1171CQ#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1171CQ#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1171CQ#PBF?
LT1171CQ#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1171CQ#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 LT1171CQ#PBF?
For technical support, including LT1171CQ#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1171CQ#PBF requirements.
6.How does Aetrix verify that LT1171CQ#PBF is sourced from the original manufacturer or authorized distributors?
All LT1171CQ#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 LT1171CQ#PBF meets industry standards.
7.What is the process for return or replacement of LT1171CQ#PBF?
All LT1171CQ#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1171CQ#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 LT1171CQ#PBF part is unused and in its original packaging.
Return procedure for LT1171CQ#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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