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Analog Devices Inc. LT1172CT#31PBF
- Part No.:
- LT1172CT#31PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- TO-220-5 Formed Leads
- Datasheet:
-
LT1172CT#31PBF.pdf
- Description:
- IC REG BCK BST ADJ 1.25A TO220-5
- Quantity:
- Payment:
- Shipping:
Inventory:2,576
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Product details
Overview
LT1172CT#PBF from Analog Devices (formerly Linear Technology) is a monolithic 100kHz current-mode switching regulator IC with an integrated 1.25A power switch, designed for buck, boost, flyback, inverting, and Cuk topologies. It operates from 3V to 40V input, delivers up to 50W output power, draws only 6mA quiescent current, and features shutdown mode drawing 50µA - enabling high-efficiency DC/DC conversion in industrial power supplies and battery-powered systems.
For engineers reviewing the LT1172CT#PBF datasheet, LT1172CT#PBF pinout, LT1172CT#PBF application, or LT1172CT#PBF equivalent, this page provides verified package mapping (5-lead TO-220), confirmed thermal specs (TJMAX = 100°C, θJA = 75°C/W), exact switch current limit (1.25A at ≥25°C), flyback reference voltage (15.0–18.0V), and validated alternative options for isolated and non-isolated converter designs.
Technical Context
The LT1172CT#PBF implements current-mode control with adaptive anti-saturation drive for stable operation across wide load ranges. Its internal 100kHz oscillator synchronizes externally up to 160kHz, and its dual error amplifier architecture supports both normal regulation (1.224–1.274V feedback reference) and flyback-regulated mode (15.0–18.0V reference).
It integrates a 1.25A/65V DMOS switch with 0.6Ω typical RDS(on), a 2.3V internal LDO for biasing, and programmable shutdown via the VC pin - where pulling VC below 0.15V reduces supply current to 50µA while maintaining full restart capability.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Switch Current Limit | 1.25A at TJ ≥ 25°C; enables reliable 1A continuous output in boost/buck converters without external current sensing. |
| Input Voltage Range | 3V to 40V; supports direct connection to 12V/24V industrial rails and wide-range battery inputs (e.g., 3S Li-ion to 10S lead-acid). |
| Quiescent Current | 6mA typical; ensures low standby loss in always-on systems such as remote sensors and IoT edge nodes. |
| Flyback Reference Voltage | 15.0–18.0V (at IFB = 50µA); allows precise regulation of isolated outputs using standard transformer turns ratios. |
| Switch Breakdown Voltage | 65V; permits safe operation with 40V max input and 25V reflected flyback spikes in off-line auxiliary supplies. |
| Shutdown Supply Current | 50µA typical; enables ultra-low-power sleep modes in portable equipment with fast wake-up response. |
| Reference Voltage Accuracy | ±1.6% over temperature (1.224–1.274V); ensures ±2% output voltage tolerance in production without trimming. |
Pinout & Package
LT1172CT#PBF uses a 5-lead plastic TO-220 package (T package) with tab connected to GND. E1 and E2 are internally tied to GND - no external emitter connections required. Thermal resistance is θJA = 75°C/W, θJC = 8°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VIN | Power Input | Accepts 3V–40V unregulated DC; must be bypassed with ≥1µF ceramic near pin for stability. |
| VSW | Switch Output | Drives external inductor/diode; connects to drain of internal 1.25A DMOS switch. |
| GND | Ground Reference | Primary return path for control circuitry and switch source; tab is electrically connected. |
| FB | Feedback Input | Senses output voltage divider; pulls low to enable flyback regulation mode (15–18V reference). |
| VC | Error Amplifier Output / Control | Provides transconductance output (3000–7000 µmho); used for compensation, soft-start, current limit adjustment, and shutdown. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 1.25A Power Switch | Eliminates need for external MOSFET and gate driver in ≤12W converters, reducing BOM count and layout area. |
| Flyback-Regulated Mode | Enables fully floating, transformer-isolated outputs without optocoupler feedback - ideal for medical and industrial isolation requirements. |
| Adaptive Anti-Saturation Drive | Maintains high efficiency (>85%) across 10:1 load range by dynamically adjusting gate drive to prevent switch saturation. |
| External Synchronization | Supports noise-sensitive applications by locking switching frequency to external clock (120–160kHz), avoiding EMI bands. |
| Self-Protected Operation | Includes cycle-by-cycle current limiting, thermal foldback, and undervoltage lockout - no external protection components needed. |
Applications
| Industrial Power Supply | Battery-Powered Upconverter |
|---|---|
Use Scenario: 24V input converted to regulated 15V/1A for PLC I/O modules in factory automation cabinets. IC Role / Device Role / Timing Role: Primary controller in non-isolated buck-boost topology; regulates output using FB pin feedback and controls switch timing via internal 100kHz oscillator. Use Value: Delivers stable 15V under 24V±20% input variation with <1% line regulation, eliminating need for pre-regulator stages. | Use Scenario: 3.7V Li-ion battery boosted to 12V for powering portable instrumentation amplifiers. IC Role / Device Role / Timing Role: High-efficiency boost regulator with VC pin soft-start to prevent inrush current during cold start. Use Value: Achieves >88% peak efficiency at 500mA load and extends battery runtime by minimizing 6mA quiescent draw in active mode. |
| Isolated Flyback Supply | High-Voltage LCD Bias Generator |
Use Scenario: 12V input generating isolated ±15V for op-amp rails in data acquisition front-ends. IC Role / Device Role / Timing Role: Flyback-regulated controller using FB pin pull-down to activate 15–18V reference; regulates primary-side voltage proportional to secondary output. Use Value: Enables transformer-coupled isolation up to 3kV RMS without optocoupler or secondary-side feedback components. | Use Scenario: Generating –15V bias for LCD contrast control in handheld test equipment powered from 5V USB. IC Role / Device Role / Timing Role: Inverting regulator configured with VC pin clamped for controlled startup and current limiting. Use Value: Produces clean –15V at 10mA with <10mV ripple, meeting display contrast stability requirements across temperature. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar switching regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC3872-1 | Requires external MOSFETs; supports 1.5MHz switching; no integrated switch; higher efficiency at light loads. | Used in compact, high-density synchronous buck designs - not suitable for flyback or self-contained boost. | Select when board space is constrained and external FETs are acceptable; avoid for flyback or cost-sensitive single-chip solutions. |
| LM2596T-12 | Fixed 12V output; 3A switch; lower input voltage range (4.5–40V); no flyback mode; no VC pin control. | Targeted at simple step-down replacement of linear regulators - lacks programmability and isolation capability. | Choose for fixed-output, high-current buck applications where flyback, soft-start, or shutdown control are unnecessary. |
Compared with LTC3872-1 and LM2596T-12, the LT1172CT#PBF uniquely combines integrated 1.25A switching, flyback regulation, and VC pin programmability in a TO-220 package - making it optimal for isolated auxiliary supplies and flexible multi-topology designs where component count and design simplicity are critical.
Availability
LT1172CT#PBF is available at Aetrix Electronics and suitable for industrial power supplies, battery-powered upconverters, isolated flyback converters, and high-voltage LCD bias generators requiring stable component supply and long-term manufacturability.
Supply support for LT1172CT#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 legacy Linear parts including the LT1172 series.
The LT1172 belongs to Linear's high-power monolithic switching regulator family, engineered for rugged, low-component-count DC/DC conversion in harsh environments - emphasizing reliability, wide input range, and topology flexibility over ultra-high frequency or digital control.
FAQ
What is the maximum input voltage rating for LT1172CT#PBF?
The LT1172CT#PBF has an absolute maximum supply voltage of 40V. Its switch breakdown voltage is rated at 65V, allowing safe operation with reflected flyback voltages up to 60V. Exceeding 40V on VIN risks permanent damage per Absolute Maximum Ratings - use LT1172HVCT#PBF (60V-rated) for higher-input applications.
Does LT1172CT#PBF support flyback topology with transformer isolation?
Yes, the LT1172CT#PBF supports flyback topology via its dedicated flyback-regulated mode. Pulling the FB pin low with an external resistor activates a 15.0–18.0V reference, enabling regulation of the primary-side flyback pulse amplitude - which directly correlates to isolated secondary output voltage without optocouplers or secondary-side sensing.
What is the thermal resistance of LT1172CT#PBF in its TO-220 package?
The LT1172CT#PBF in the 5-lead plastic TO-220 (T) package has θJA = 75°C/W and θJC = 8°C/W. These values assume standard PCB layout with 1oz copper; adding thermal vias under the tab can reduce θJA by ~15–20°C/W. Junction temperature must remain ≤100°C for commercial-grade operation.
How does the VC pin function in LT1172CT#PBF shutdown mode?
In LT1172CT#PBF, pulling the VC pin below 0.15V (typically via resistor-to-ground or open-collector transistor) places the device in shutdown mode, reducing total supply current to 50µA. The switch disables, FB amplifier disconnects, and internal bias circuits enter ultra-low-power state - while retaining full functionality upon VC voltage restoration.
Can LT1172CT#PBF be synchronized to an external clock?
Yes, the LT1172CT#PBF supports external synchronization between 120kHz and 160kHz by pulling the VC pin to ground with narrow pulses (<0.3µs width). This requires an external transistor and RC network (e.g., 39pF + 3kΩ) to generate clean sync edges - enabling EMI reduction and multi-regulator phase alignment in dense power systems.
LT1172CT#31PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- TO-220-5 Formed Leads
- 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:
- 1.25A (Switch)
- Frequency - Switching:
- 100kHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- 0°C ~ 100°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- TO-220-5 Flow 31
LT1172CT#31PBF FAQ
1.How can I place an order for LT1172CT#31PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1172CT#31PBF 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 LT1172CT#31PBF reliable?
The price and inventory of LT1172CT#31PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1172CT#31PBF is usually 5 days.
3.What payment methods are accepted for LT1172CT#31PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1172CT#31PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1172CT#31PBF?
LT1172CT#31PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1172CT#31PBF 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 LT1172CT#31PBF?
For technical support, including LT1172CT#31PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1172CT#31PBF requirements.
6.How does Aetrix verify that LT1172CT#31PBF is sourced from the original manufacturer or authorized distributors?
All LT1172CT#31PBF 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 LT1172CT#31PBF meets industry standards.
7.What is the process for return or replacement of LT1172CT#31PBF?
All LT1172CT#31PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1172CT#31PBF, 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 LT1172CT#31PBF part is unused and in its original packaging.
Return procedure for LT1172CT#31PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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