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Analog Devices Inc. LT1172IS8#PBF
- Part No.:
- LT1172IS8#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1172IS8#PBF.pdf
- Description:
- IC REG BUCK BOOST ADJ 1.25A 8SO
- Quantity:
- Payment:
- Shipping:
Inventory:904
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Product details
Overview
LT1172IS8#PBF from Analog Devices (formerly Linear Technology) is a monolithic 100kHz current-mode switching regulator IC with integrated 1.25A switch, designed for buck, boost, flyback, inverting, and Cuk topologies. It operates from 3V to 60V input, delivers up to 25W output power (in buck mode), draws only 6mA quiescent current, and features shutdown mode drawing 50µA - enabling use in battery-powered industrial power supplies and isolated DC-DC converters.
For engineers reviewing the LT1172IS8#PBF datasheet, LT1172IS8#PBF pinout, LT1172IS8#PBF application, or LT1172IS8#PBF equivalent, key selection criteria include its −40°C to +100°C operating temperature range, 8-pin PDIP/SO package with separate emitter pins (E1/E2), internal 1.24V reference, flyback-regulation capability, and adaptive anti-saturation switch drive for wide load-current efficiency retention.
Technical Context
The LT1172IS8#PBF implements current-mode control with a fixed 100kHz oscillator, where switch duty cycle is directly set by sensed switch current against a VC-pin-controlled threshold. Its dual error amplifiers support both normal regulation (via FB pin at 1.24V) and isolated flyback mode (FB pulled low, regulating at 15V ±1.3V).
It integrates a 1.25A/60V rated NPN power switch with 1Ω max on-resistance, adaptive anti-saturation driver, 2.3V internal LDO for biasing, and thermal protection. Pin E2 enables switch current limit reduction by disconnecting the second emitter - a feature unique to the 8-pin S8/N8 packages and critical for thermal management in miniDIP layouts.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Switch Current Limit | 1.25A typical at 50% duty cycle; drops to 1.0A below 25°C junction - defines maximum continuous output current in buck/boost configurations. |
| Input Voltage Range | 3V to 60V - supports wide-range industrial, automotive, and battery-input systems without external pre-regulation. |
| Reference Voltage | 1.24V ±20mV - sets output voltage accuracy in standard feedback loops using resistor dividers. |
| Flyback Reference | 15.0V ±1.3V - enables transformer-isolated regulation without optocoupler or secondary-side sensing. |
| Quiescent Current | 6mA - enables high-efficiency operation at light loads; reduces no-load power loss in always-on systems. |
| Shutdown Current | 50µA - allows ultra-low-power standby in portable or energy-sensitive applications. |
| Switch Breakdown Voltage | 60V - limits maximum safe input voltage in non-HV variants; requires derating for flyback topologies with leakage spikes. |
| Switch On-Resistance | 1.0Ω max - determines conduction loss and thermal rise; doubles when E2 is left unconnected. |
Pinout & Package
LT1172IS8#PBF is housed in an 8-pin plastic DIP (N8) or plastic SO (S8) package with exposed ground tab. The package includes two dedicated emitter terminals (E1, E2) for precision current sensing and configurable current limiting - a key differentiator from 5-pin TO-220 or TO-3 variants.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| GND (Pin 1) | Power and signal ground reference | Primary ground return; must be connected to PCB ground plane with low-inductance path. |
| VC (Pin 2) | Error amplifier output / control node | Sets switch current limit; used for soft-start (capacitor), shutdown (≤0.15V), and frequency compensation (RC network). |
| FB (Pin 3) | Feedback input | Compares output voltage to 1.24V reference; pulling below 0.45V selects flyback mode (15V reference). |
| NC (Pin 4) | No connect | Internally unused; must remain unconnected per datasheet - not for grounding or routing. |
| E2 (Pin 5) | Secondary emitter terminal | Optional connection; disconnecting E2 halves switch current limit and doubles RON, reducing dissipation during overload. |
| VSW (Pin 6) | Switch collector output | Drives external inductor/diode; handles peak currents up to 3.5A in pulse mode; requires snubber in flyback. |
| E1 (Pin 7) | Primary emitter terminal | Mandatory ground connection for switch emitter; ties internally to GND pin - must always be connected. |
| VIN (Pin 8) | Input supply voltage | Accepts 3–60V; powers internal LDO and switch; requires local 1µF ceramic bypass near pin. |
Key Features
| Feature | Design Value |
|---|---|
| Adaptive anti-saturation switch drive | Minimizes switch turn-off time and driver dissipation across 0.1–1.25A load range, preserving efficiency without external gate control. |
| Dual-mode error amplification | Supports both standard 1.24V feedback and isolated 15V flyback regulation via single FB pin - eliminates need for optocouplers in AC/DC adapters. |
| Separate emitter terminals (E1/E2) | Enables precise current limit adjustment and thermal optimization in 8-pin packages - critical for miniDIP reliability at full load. |
| Self-protected overload handling | Includes current-mode pulse-by-pulse limiting and thermal foldback - prevents damage during output shorts without external current-sense resistors. |
| External synchronization capability | Accepts 120–160kHz sync pulses on VC pin - allows noise-sensitive designs to avoid EMI bands or synchronize multiple regulators. |
Applications
| Battery-Powered Boost Supply | Isolated Flyback Converter |
|---|---|
Use Scenario: Generating 12V from a 3.6V Li-ion battery for MCU peripherals and sensors in portable test equipment. IC Role / Device Role: Primary controller in boost topology; regulates output using FB divider while managing battery discharge profile. Use Value: 6mA quiescent current extends battery life; 1.25A switch supports >1A output; shutdown mode reduces standby draw to 50µA. | Use Scenario: Providing isolated 5V/6A and ±15V rails from 24V industrial bus in PLC I/O modules. IC Role / Device Role: Flyback controller regulating primary-side reflected voltage; uses FB pin in low-threshold mode to enable transformer-coupled feedback. Use Value: Eliminates optocoupler and secondary-side TL431, reducing BOM cost and improving long-term stability of isolated outputs. |
| Inverting Power Supply | High-Voltage LCD Bias Generator |
Use Scenario: Generating −15V from +12V rail for op-amp biasing in analog signal conditioning circuits. IC Role / Device Role: Inverting topology controller; VIN = +12V, VOUT = −15V; uses standard inductor-diode-capacitor layout. Use Value: Single-chip solution avoids discrete transistor+driver complexity; current-mode control ensures stable regulation under varying load transients. | Use Scenario: Producing −10V to −26V adjustable contrast voltage for industrial LCD displays powered from 3–20V battery or adapter input. IC Role / Device Role: Inverting charge-pump-like configuration with external FET (VN2222) and timing capacitor; regulated via FB divider. Use Value: Wide input range accommodates aging batteries; shutdown pin (via R3) enables display blanking to conserve power. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar switching regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT1172CS8#PBF | Same silicon, 0°C to +100°C temp grade vs. −40°C to +100°C for LT1172IS8#PBF; identical pinout and electrical specs. | Not suitable for extended cold environments (e.g., outdoor industrial sensors, automotive under-hood). | Select LT1172IS8#PBF when operation below 0°C is required; CS8 is lower-cost alternative for commercial-temperature-only designs. |
| LM2574HVS-12 | Fixed 12V output, 52kHz switching, 0.5A switch, SO-8 package; no flyback mode or dual emitters. | Lacks programmable output, isolated regulation, and current-limit flexibility - limited to simple step-down applications. | Choose LM2574HVS-12 only for cost-sensitive, fixed-output, non-isolated 12V supplies where design simplicity outweighs feature requirements. |
Compared with LT1172CS8#PBF, the LT1172IS8#PBF adds guaranteed operation down to −40°C - essential for harsh-environment deployments. Versus LM2574HVS-12, it offers full topology flexibility, flyback isolation, and user-configurable current limiting via E2, at the cost of higher design complexity.
Availability
LT1172IS8#PBF is available at Aetrix Electronics and suitable for industrial power supplies, isolated DC-DC converters, battery-upconverter systems, and programmable voltage sources requiring stable component supply across extended temperature ranges.
Supply support for LT1172IS8#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 space-constrained, high-reliability power conversion - especially where topology flexibility, wide input range, and self-protected operation are critical.
FAQ
What is the maximum input voltage rating for LT1172IS8#PBF?
The absolute maximum supply voltage for LT1172IS8#PBF is 60V, but the recommended maximum operating input voltage is 40V for standard-grade devices. In flyback configurations, input must be limited to ≤55V to avoid switch breakdown due to leakage inductance spikes - consult AN19 for transformer design guidelines specific to LT1172IS8#PBF.
Can LT1172IS8#PBF be used in flyback topology without an optocoupler?
Yes, LT1172IS8#PBF supports optocoupler-free flyback regulation by pulling the FB pin below 0.45V to activate its internal 15V flyback reference amplifier. This allows regulation based on reflected primary-side voltage, eliminating secondary-side feedback components - a key capability confirmed in the LT1172IS8#PBF datasheet Figure TA03 and Block Diagram.
What is the purpose of the NC pin (Pin 4) on LT1172IS8#PBF?
Pin 4 on LT1172IS8#PBF is designated NC (No Connect) and must remain unconnected. The datasheet explicitly states this pin may become active in future revisions and warns against routing or grounding it. Connecting Pin 4 risks undefined behavior or damage, as it has no internal function in the current LT1172IS8#PBF silicon revision.
How does disconnecting E2 affect LT1172IS8#PBF performance?
Disconnecting E2 on LT1172IS8#PBF reduces the switch current limit by 2:1 (to ~0.625A) and doubles the on-resistance (to ~2Ω), decreasing conduction loss during overload but increasing steady-state dissipation above 300mA. This trade-off is documented in the LT1172IS8#PBF datasheet Section "Extra Pins on the MiniDIP and Surface Mount Packages" as a thermal management technique for miniDIP layouts.
Is LT1172IS8#PBF RoHS-compliant and lead-free?
Yes, LT1172IS8#PBF is RoHS-compliant and features a lead-free finish, as indicated by the "#PBF" suffix in the part number per Analog Devices' packaging nomenclature. The device meets JEDEC J-STD-020 moisture sensitivity level (MSL) requirements for plastic SO and PDIP packages and is qualified for reflow soldering per industry standards.
LT1172IS8#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- 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:
- -40°C ~ 100°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SO
LT1172IS8#PBF FAQ
1.How can I place an order for LT1172IS8#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1172IS8#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 LT1172IS8#PBF reliable?
The price and inventory of LT1172IS8#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1172IS8#PBF is usually 5 days.
3.What payment methods are accepted for LT1172IS8#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1172IS8#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1172IS8#PBF?
LT1172IS8#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1172IS8#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 LT1172IS8#PBF?
For technical support, including LT1172IS8#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1172IS8#PBF requirements.
6.How does Aetrix verify that LT1172IS8#PBF is sourced from the original manufacturer or authorized distributors?
All LT1172IS8#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 LT1172IS8#PBF meets industry standards.
7.What is the process for return or replacement of LT1172IS8#PBF?
All LT1172IS8#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1172IS8#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 LT1172IS8#PBF part is unused and in its original packaging.
Return procedure for LT1172IS8#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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