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Analog Devices Inc. LT1172CS8#TRPBF
- Part No.:
- LT1172CS8#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1172CS8#TRPBF.pdf
- Description:
- IC REG BUCK BOOST ADJ 1.25A 8SO
- Quantity:
- Payment:
- Shipping:
Inventory:1,722
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Product details
Overview
LT1172CS8#TRPBF 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 25W output power in boost mode, draws only 6mA quiescent current, and supports flyback-regulated isolated outputs - used in industrial DC-DC conversion where compact high-voltage isolation is required.
For engineers reviewing the LT1172CS8#TRPBF datasheet, LT1172CS8#TRPBF pinout, LT1172CS8#TRPBF application, or LT1172CS8#TRPBF equivalent, key selection criteria include its 8-pin SOIC package, internal 1.25A/60V switch, flyback reference voltage of 15.0V (±1.3V), shutdown threshold of 50mV, and compatibility with standard 5V logic control signals.
Technical Context
The LT1172CS8#TRPBF implements current-mode control with adaptive anti-saturation drive, enabling stable operation across wide load ranges without efficiency loss. Its dual error amplifier architecture supports both normal regulation (1.224V feedback reference) and flyback mode (15.0V reference), with separate VC pin control for soft-start, current limit adjustment, and shutdown.
It features internal 100kHz oscillator timing, 85–97% maximum duty cycle, and dedicated E1/E2 emitter terminals for precision ground referencing in the 8-pin SOIC (S8) package - allowing external current limit scaling and reduced ground-path error in high-current flyback designs.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Switch Current Limit | 1.25A typical at 50% duty cycle; enables reliable 1A continuous output in boost/flyback with thermal derating. |
| Input Voltage Range | 3V to 40V - supports wide-range industrial inputs including 5V logic rails, 12V/24V systems, and battery-backed supplies. |
| Feedback Reference | 1.224V (normal mode); sets precise output voltage via resistor divider; ±0.02V tolerance ensures <1% output regulation error. |
| Flyback Reference | 15.0V (±1.3V); allows direct regulation of transformer-coupled isolated outputs without optocoupler feedback. |
| Quiescent Current | 6mA - enables low-power standby operation; reduces no-load losses in always-on embedded power supplies. |
| Shutdown Current | 50µA - achieves ultra-low power state for battery-powered systems requiring extended sleep modes. |
| Switch Breakdown Voltage | 60V - limits maximum input to 60V in non-HV variants; defines safe operating area for 48V bus applications. |
| Switch On-Resistance | 0.6Ω max - determines conduction loss; at 1A, contributes ≤0.6W dissipation, critical for thermal design in S8 package. |
Pinout & Package
LT1172CS8#TRPBF is housed in an 8-lead plastic SOIC (S8) package with exposed thermal pad (JEDEC MS-012), rated θJA = 120–150°C/W depending on PCB copper area. Pin 4 (NC) must remain unconnected per datasheet.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| GND (Pin 1) | Power and signal ground reference | Primary return path for switch current and control circuitry; connects to E1 internally in TO-220/TO-3 packages. |
| VC (Pin 2) | Error amplifier output / control node | Used for frequency compensation, soft-start (capacitor), current limit clamping (voltage), and shutdown (≤0.15V). |
| FB (Pin 3) | Feedback input | Compares output voltage to 1.224V reference (normal) or 15.0V (flyback); threshold at 0.45V selects flyback mode. |
| NC (Pin 4) | No connect | Not bonded; must be left floating - future revision may assign function; connecting risks undefined behavior. |
| E2 (Pin 5) | Secondary emitter terminal | Optional connection to reduce current limit by 2×; open-circuit doubles RDS(on) to ~1.2Ω, increasing conduction loss above 300mA. |
| VSW (Pin 6) | Switch collector output | Drives external inductor/diode; handles peak currents up to 3.5A during current limiting; 60V breakdown rating. |
| E1 (Pin 7) | Primary emitter terminal | Mandatory ground connection for switch emitter; ties to GND pin internally in non-S8 packages; minimizes ground bounce in high-dI/dt paths. |
| VIN (Pin 8) | Main supply input | Accepts 3–40V; powers internal 2.3V regulator and switch driver; requires local 1µF ceramic bypass near pin. |
Key Features
| Feature | Design Value |
|---|---|
| Current-mode switching architecture | Enables immediate line transient response and simplifies loop compensation across 10:1 input/output ratios. |
| Adaptive anti-saturation switch drive | Maintains high efficiency from light to full load by dynamically adjusting base drive to prevent BJT saturation. |
| Dual-mode error amplifiers | Supports both standard buck/boost regulation and transformer-isolated flyback without external op-amps or optocouplers. |
| Separate E1/E2 emitter pins | Eliminates ground-path voltage drop errors in high-current flyback designs and enables programmable current limiting. |
| External synchronization capability | Accepts 120–160kHz sync pulses on VC pin for EMI reduction in multi-regulator systems. |
| Self-protected overload handling | Integrates pulse-by-pulse current limiting, thermal foldback, and shutdown - no external protection components needed. |
Applications
| Industrial DC-DC Conversion | Isolated Flyback Power Supply |
|---|---|
Use Scenario: Converting 12V or 24V factory bus to regulated 5V/3.3V for PLC I/O modules and sensor interfaces. IC Role / Device Role / Timing Role: Primary controller in non-isolated buck-boost topology; regulates output using internal 1.224V reference and current-mode PWM. Use Value: Eliminates need for external MOSFET drivers and current sense resistors; achieves >85% efficiency at 1A load with minimal BOM count. | Use Scenario: Generating ±15V isolated op-amp supplies from a single 5V rail in test equipment. IC Role / Device Role / Timing Role: Flyback controller regulating secondary winding voltage via primary-side sensing; uses 15.0V flyback reference and FB pin threshold. Use Value: Enables fully floating outputs up to transformer breakdown voltage; removes optocoupler and TL431, reducing cost and board space by 30%. |
| Battery Upconverter | Logic-Level Inverter Supply |
Use Scenario: Boosting 3.6V Li-ion battery to 12V for motor drivers in portable instrumentation. IC Role / Device Role / Timing Role: High-efficiency boost converter with adaptive anti-sat drive; maintains >82% efficiency down to 0.1A load. Use Value: 6mA quiescent current extends battery runtime; shutdown mode draws only 50µA, enabling weeks of standby time. | Use Scenario: Generating –10V to –26V negative bias for LCD contrast control in handheld medical devices. IC Role / Device Role / Timing Role: Inverting regulator using internal switch and external diode/capacitor; controlled via FB pin and VC soft-start. Use Value: Single-chip solution replaces discrete charge-pump ICs; adjustable output via R1/R2 divider; supports 5V logic-compatible enable/shutdown. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar switching regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT1172CN8#TRPBF | Same electrical specs and pinout; differs only in packaging - PDIP instead of SOIC; higher θJA (130°C/W vs 120–150°C/W). | Preferred for through-hole prototyping or legacy board rework; unsuitable for high-density surface-mount production. | Select when manual assembly, thermal margin >20°C, or existing DIP footprint exists. |
| LT1172CT#TRPBF | TO-220-5 package; same die but higher thermal performance (θJA = 75°C/W); includes tab-as-GND; no E2 pin. | Required for >1.5A continuous output or ambient >60°C; lacks E2 flexibility but offers superior heat dissipation. | Select for high-power industrial converters needing heatsink mounting and no emitter splitting. |
Compared with LT1172CN8#TRPBF and LT1172CT#TRPBF, the LT1172CS8#TRPBF provides optimal surface-mount integration with E2-based current limit tuning, while maintaining identical regulation accuracy and flyback capability - making it ideal for space-constrained isolated DC-DC modules.
Availability
LT1172CS8#TRPBF is available at Aetrix Electronics and suitable for industrial DC-DC conversion, isolated flyback power supplies, and battery upconverter applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.
Supply support for LT1172CS8#TRPBF 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 cost-sensitive industrial and embedded systems where simplicity, reliability, and topology flexibility outweigh the need for ultra-high efficiency or MHz switching.
FAQ
What is the maximum input voltage rating for the LT1172CS8#TRPBF?
The LT1172CS8#TRPBF has an absolute maximum supply voltage of 40V. Exceeding this risks permanent damage. The switch breakdown voltage is rated at 60V, but the input supply pin (VIN) is limited to 40V per Absolute Maximum Ratings. For 60V input applications, the HV-grade variant LT1172HVCS8#TRPBF must be used instead.
Can the LT1172CS8#TRPBF be used in flyback topology without an optocoupler?
Yes, the LT1172CS8#TRPBF supports optocoupler-free flyback regulation using its dedicated flyback error amplifier and 15.0V reference voltage. When the FB pin is pulled below 0.45V, it activates flyback mode and regulates the reflected flyback pulse amplitude - enabling fully isolated outputs with transformer turns-ratio-based voltage setting.
What is the purpose of the NC pin (Pin 4) on the LT1172CS8#TRPBF?
Pin 4 on the LT1172CS8#TRPBF is designated NC (No Connect) and must remain unconnected. The datasheet explicitly states it is not bonded and may be assigned functionality in future revisions. Connecting Pin 4 risks undefined operation or latch-up; it serves no electrical function in the current LT1172CS8#TRPBF silicon revision.
How does the E1/E2 pin configuration affect current limiting in the LT1172CS8#TRPBF?
Leaving E2 open on the LT1172CS8#TRPBF reduces the effective current limit by 2× (to ~0.625A) but doubles the switch on-resistance to ~1.2Ω. This trade-off lowers I²R dissipation during overload while increasing conduction loss at normal loads - useful for protecting downstream circuits without adding external current-limiting components.
Is the LT1172CS8#TRPBF pin-compatible with other LT117x variants in the same package?
Yes, all LT117x parts in the S8 (8-lead SOIC) package - including LT1170CS8#TRPBF, LT1171CS8#TRPBF, and LT1172CS8#TRPBF - share identical pinouts and footprint. However, their internal switch ratings differ (5A/2.5A/1.25A), so substituting without verifying current/power requirements may cause thermal failure or regulation loss.
LT1172CS8#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- 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:
- Surface Mount
- Supplier Device Package:
- 8-SO
LT1172CS8#TRPBF FAQ
1.How can I place an order for LT1172CS8#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1172CS8#TRPBF 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 LT1172CS8#TRPBF reliable?
The price and inventory of LT1172CS8#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1172CS8#TRPBF is usually 5 days.
3.What payment methods are accepted for LT1172CS8#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1172CS8#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1172CS8#TRPBF?
LT1172CS8#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1172CS8#TRPBF 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 LT1172CS8#TRPBF?
For technical support, including LT1172CS8#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1172CS8#TRPBF requirements.
6.How does Aetrix verify that LT1172CS8#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT1172CS8#TRPBF 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 LT1172CS8#TRPBF meets industry standards.
7.What is the process for return or replacement of LT1172CS8#TRPBF?
All LT1172CS8#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1172CS8#TRPBF, 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 LT1172CS8#TRPBF part is unused and in its original packaging.
Return procedure for LT1172CS8#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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