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Analog Devices Inc. LT1172CS8#PBF
- Part No.:
- LT1172CS8#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1172CS8#PBF.pdf
- Description:
- IC REG BUCK BOOST ADJ 1.25A 8SO
- Quantity:
- Payment:
- Shipping:
Inventory:2,569
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Product details
Overview
LT1172CS8#PBF from Analog Devices (formerly Linear Technology) is a monolithic 1.25A current-mode switching regulator IC in an 8-lead plastic DIP package, operating from 3V to 40V input, delivering up to 25W in buck/boost/flyback topologies with 100kHz fixed-frequency switching, 6mA quiescent current, and internal switch with 1Ω max on-resistance - used in isolated DC-DC converters for industrial power supplies.
For engineers reviewing the LT1172CS8#PBF datasheet, LT1172CS8#PBF pinout, LT1172CS8#PBF application, or LT1172CS8#PBF equivalent, this page provides verified functional identity, validated 8-pin DIP terminal roles, confirmed flyback/buck-boost operation, thermal derating guidance for plastic DIP, and two field-validated alternative parts with documented parameter and topology differences.
Technical Context
The LT1172CS8#PBF implements current-mode control with adaptive anti-saturation drive for the integrated NPN power switch, enabling stable regulation across wide load ranges without external compensation complexity. Its dual error amplifier architecture supports both normal (1.24V feedback reference) and flyback modes (15V–18V programmable reference), with separate VC pin for soft-start, current limit adjustment, and shutdown.
It features internal 2.3V low-dropout bias regulator, 100kHz oscillator, and dedicated E1/E2 emitter pins for ground-path isolation in miniDIP packages - allowing configurable current limiting and reduced ground-loop error in transformer-coupled designs. Flyback blanking time is 1.5µs to reject leakage spikes.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3V to 40V - enables direct operation from 5V logic rails up to 36V industrial buses without pre-regulation. |
| Switch Current Limit | 1.25A typical at 50% duty cycle - sets maximum output power ceiling in buck/boost; derates to 1.0A below 25°C junction. |
| Reference Voltage | 1.244V ±20mV - precision bandgap reference for accurate output voltage setting via resistive divider. |
| Quiescent Current | 6mA - ensures low standby loss in always-on systems; drops to 50µA in shutdown mode. |
| Switch On-Resistance | 1.00Ω max - determines conduction loss and thermal rise; doubles if E2 emitter is left unconnected. |
| Switching Frequency | 100kHz ±12kHz - balances efficiency vs. magnetics size; externally synchronizable to 120–160kHz. |
| Flyback Reference | 15.0–18.0V - enables isolated output regulation without optocoupler feedback in flyback topologies. |
Pinout & Package
LT1172CS8#PBF uses an 8-lead plastic DIP (N8) package with 100°C/W thermal resistance. Pin 4 (NC) must remain unconnected per datasheet; E1 and E2 are dedicated emitter terminals for improved current sensing and configurable current limiting.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| GND (Pin 1) | Power and signal ground reference | Primary return path for internal regulators and error amplifier; connect directly to PCB ground plane. |
| VC (Pin 2) | Error amplifier output / control node | Used for frequency compensation, soft-start (via capacitor), current limit clamping, and shutdown (pull <0.15V). |
| FB (Pin 3) | Feedback input | Compares output-derived voltage to 1.244V reference; pulled low to enable flyback mode (15–18V ref). |
| NC (Pin 4) | No connection | Not internally bonded; must be left floating - not tied to GND or any other net. |
| E2 (Pin 5) | Secondary emitter terminal | Optional connection; disconnecting E2 halves current limit but doubles RDS(on), increasing conduction loss above 300mA. |
| VSW (Pin 6) | Switch collector output | Drives external inductor/diode network; rated for 65V breakdown (LT1172S8 variant). |
| E1 (Pin 7) | Primary emitter terminal | Mandatory ground connection for switch emitter; always tie to GND pin (Pin 1) on PCB. |
| VIN (Pin 8) | Input supply rail | Accepts 3–40V; powers internal 2.3V LDO and oscillator; bypass with ≥1µF ceramic near pin. |
Key Features
| Feature | Design Value |
|---|---|
| Integrated 1.25A switch with adaptive anti-sat drive | Enables robust overload handling without external current sense resistor or complex gate drive circuitry. |
| Dual-mode error amplifiers (normal + flyback) | Supports both direct-output regulation and fully floating isolated outputs using transformer-coupled flyback topology. |
| Dedicated E1/E2 emitter pins | Eliminates ground-path voltage drop errors and allows user-selectable 2:1 current limit reduction by leaving E2 open. |
| External synchronization capability (120–160kHz) | Permits noise-sensitive systems to avoid EMI bands or synchronize multiple regulators without phase jitter. |
| Self-protected against overloads and thermal faults | Includes cycle-by-cycle current limiting and inherent thermal foldback - no external protection components required. |
Applications
| Industrial Isolated Power Supply | LCD Contrast Voltage Generator |
|---|---|
Use Scenario: Generating ±15V isolated auxiliary rails from a 24V industrial bus for op-amp biasing in PLC I/O modules. IC Role / Device Role / Timing Role: Primary-side controller in flyback topology regulating secondary output via primary-side sensing; operates at 100kHz with 1.5µs blanking. Use Value: Eliminates optocoupler and TL431, reducing BOM count and improving long-term stability of isolated output voltage. | Use Scenario: Producing adjustable negative voltage (–10V to –26V) from a 3–20V battery source for LCD contrast control in portable medical displays. IC Role / Device Role / Timing Role: Inverting buck-boost regulator with shutdown control; FB pin pulled low to enable high-voltage flyback reference mode. Use Value: Achieves precise contrast tuning with single external potentiometer while maintaining ultra-low quiescent draw (6mA) during display idle periods. |
| Battery-Powered Upconverter | Logic-to-Analog Supply Converter |
Use Scenario: Boosting 3.7V Li-ion battery voltage to 12V for powering small solenoids or sensors in handheld test equipment. IC Role / Device Role / Timing Role: Fixed-frequency boost controller with internal 1.25A switch; uses E1/E2 configuration for accurate current limiting under varying battery voltage. Use Value: Delivers full 12V/0.5A output down to 3.0V input without external MOSFET, simplifying layout and reducing footprint. | Use Scenario: Converting 5V logic supply to ±15V op-amp rails in data acquisition front-ends where noise immunity and rail symmetry matter. IC Role / Device Role / Timing Role: Dual-output flyback controller with center-tapped secondary; regulates both positive and negative rails from single transformer winding. Use Value: Ensures matched load regulation and ripple rejection between ±15V rails without independent feedback networks. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar switching regulator applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LT1172CN8#PBF | Same electrical specs and pinout; differs only in temperature grade (0°C to 100°C commercial vs. same range for CS8#PBF) and packaging (plastic DIP vs. plastic DIP - identical form factor). | No functional difference; CN8#PBF is standard-grade version; CS8#PBF denotes same spec but may reflect specific tape-and-reel or traceability marking. | Select CN8#PBF for general-purpose use; CS8#PBF is functionally interchangeable with no design changes required. |
| LT1171CN8#PBF | Higher 2.5A switch current limit, 0.5Ω max RON, same 100kHz frequency and pinout - but draws 9mA quiescent current and requires larger heatsinking in DIP package. | Suitable for higher-power boost/flyback designs (e.g., 12V@1A); not recommended where 6mA IQ or thermal budget in plastic DIP is critical. | Choose LT1171CN8#PBF only when >1.25A peak switch current is needed; verify thermal margin in N8 package at full load. |
Compared with LT1172CN8#PBF, LT1172CS8#PBF offers identical performance and fit; versus LT1171CN8#PBF, it trades 2× lower switch current and 33% lower IQ for tighter thermal compliance in space-constrained plastic DIP layouts.
Availability
LT1172CS8#PBF is available at Aetrix Electronics and suitable for industrial power supplies, battery-powered instrumentation, LCD bias generation, and isolated sensor interface circuits requiring stable component supply and long-lifecycle support.
Supply support for LT1172CS8#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 technical and manufacturing continuity for legacy Linear products including the LT117x family.
The LT117x series was designed as monolithic high-power switching regulators targeting cost-sensitive, thermally constrained applications where integration of switch, oscillator, and protection reduces external component count and improves reliability.
FAQ
What is the maximum input voltage rating for LT1172CS8#PBF?
The LT1172CS8#PBF has an absolute maximum supply voltage of 40V. Operation above this level risks permanent damage. The datasheet specifies 3V to 40V as the functional input range, with guaranteed performance across that span at junction temperatures from 0°C to 100°C. For flyback applications, the maximum safe input is further limited to 55V in HV-grade variants - but LT1172CS8#PBF is not an HV part.
Can LT1172CS8#PBF be used in flyback topology without an optocoupler?
Yes, LT1172CS8#PBF supports optocoupler-free flyback regulation via its dedicated flyback mode. When the FB pin is pulled below 0.54V, the IC switches to flyback amplifier operation with a 15–18V reference, enabling primary-side sensing of reflected output voltage. This eliminates the need for secondary-side feedback components in many isolated designs.
What is the purpose of the NC pin (Pin 4) on LT1172CS8#PBF?
Pin 4 on LT1172CS8#PBF is marked NC (No Connection) and must remain unconnected - it is not bonded internally and may become active in future revisions. Connecting it to GND, VIN, or any other node violates the datasheet and can cause unpredictable behavior or damage. This applies strictly to LT1172CS8#PBF and all LT1172 variants in 8-pin DIP/SO packages.
How does disconnecting E2 affect LT1172CS8#PBF performance?
Leaving E2 disconnected on LT1172CS8#PBF reduces peak switch current limit by 2:1 (to ~0.625A) but doubles the effective switch on-resistance (to ~2Ω), increasing conduction loss at loads above 300mA. It is useful only for intentional current limiting in low-power flyback designs where thermal margin is tight and full 1.25A capability is unnecessary.
Is LT1172CS8#PBF RoHS-compliant and lead-free?
Yes, LT1172CS8#PBF carries the #PBF suffix indicating lead-free finish and full RoHS compliance per Analog Devices' specifications. The "PBF" designation confirms termination finish meets JEDEC J-STD-609 Category 1 requirements, with no lead content exceeding 0.1% by weight in homogeneous materials.
LT1172CS8#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:
- 0°C ~ 100°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SO
LT1172CS8#PBF FAQ
1.How can I place an order for LT1172CS8#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1172CS8#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 LT1172CS8#PBF reliable?
The price and inventory of LT1172CS8#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1172CS8#PBF is usually 5 days.
3.What payment methods are accepted for LT1172CS8#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1172CS8#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1172CS8#PBF?
LT1172CS8#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1172CS8#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 LT1172CS8#PBF?
For technical support, including LT1172CS8#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1172CS8#PBF requirements.
6.How does Aetrix verify that LT1172CS8#PBF is sourced from the original manufacturer or authorized distributors?
All LT1172CS8#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 LT1172CS8#PBF meets industry standards.
7.What is the process for return or replacement of LT1172CS8#PBF?
All LT1172CS8#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1172CS8#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 LT1172CS8#PBF part is unused and in its original packaging.
Return procedure for LT1172CS8#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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