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Analog Devices Inc. LT1425IS#PBF
- Part No.:
- LT1425IS#PBF
- Manufacturer:
- Analog Devices Inc.
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LT1425IS#PBF.pdf
- Description:
- IC REG FLYBACK 135MA 16SO
- Quantity:
- Payment:
- Shipping:
Inventory:873
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Product details
Overview
LT1425IS#PBF from Analog Devices is a monolithic isolated flyback switching regulator IC designed for primary-side sensing in transformer-isolated DC/DC converters. It integrates a 1.6A/35V switch, current-mode controller, feedback amplifier, and flyback voltage sensing circuitry. Operating from 3V to 20V input, it delivers up to 6W output power without optoisolators or third-winding feedback-enabling compact, low-cost medical and telecom isolated supplies.
For engineers reviewing the LT1425IS#PBF datasheet, LT1425IS#PBF pinout, LT1425IS#PBF application, or LT1425IS#PBF equivalent, key selection considerations include its 285kHz fixed-frequency operation, ±5% output accuracy without trimming, shutdown current of 15µA, resistor-programmable output voltage, and support for load compensation via ROCOMP/RCCOMP pins.
Technical Context
The LT1425IS#PBF implements a proprietary flyback error amplifier that derives output voltage information directly from the primary-side flyback pulse waveform-eliminating need for optoisolators or auxiliary windings. Its control loop uses current-mode architecture with minimum ON-time enforcement (170ns) and programmable load compensation to maintain regulation into discontinuous conduction mode.
It features integrated 2.6V bias regulator, 285kHz oscillator with external synchronization capability (320–450kHz range), and dual ground separation (SGND for signal reference, PGND for high-current switch return). The VC pin serves as both feedback amplifier output and current comparator input, requiring external compensation capacitor to ground.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | 3V to 20V - supports wide-input industrial and telecom rails; UVLO triggers at 2.8V. |
| Switch Breakdown Voltage | 35V - enables safe operation with reflected output voltages up to ~30V on primary side. |
| Max Output Power | 6W - achievable with internal switch only; no external MOSFET required for typical isolated designs. |
| Switch Current Limit | 1.2A to 1.95A - temperature- and duty-cycle-dependent; ensures robust overcurrent protection. |
| Switching Frequency | 285kHz (typ) - fixed frequency simplifies EMI filtering; externally synchronizable up to 450kHz. |
| Quiescent Supply Current | 7mA - enables efficient light-load operation; drops to 15µA in shutdown mode. |
| Reference Current (RFB) | 402µA (typ) - sets RREF/RFB ratio for precise resistor-programmed output voltage. |
Pinout & Package
LT1425IS#PBF is housed in a 16-lead narrow SOIC package (width 3.9mm), rated for –40°C to +125°C operating junction temperature. Thermal resistance θJA = 75°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| GND (1,8,9,16) | Substrate Ground | Die substrate connection; must tie directly to low-impedance ground plane-separate from SGND/PGND. |
| RFB (3) | Flyback Feedback Input | Senses primary-side flyback pulse; current ≈400µA determines output voltage via RREF ratio. |
| VC (4) | Control Voltage Node | Output of feedback amplifier & input to current comparator; requires external compensation cap to ground. |
| RREF (5) | Reference Resistor Terminal | Ground-referred resistor (≈3.01kΩ) sets feedback gain; referenced to internal 1.22V bandgap. |
| SYNC (6) | External Clock Input | Logic-compatible sync input (1.5–2.2V min); allows EMI reduction via frequency dithering or system clock alignment. |
| SGND (7) | Signal Ground | Clean reference for internal bandgap, RREF, and VC compensation-must be isolated from power currents. |
| PGND (10) | Power Ground | Emiter return for internal switch; carries high di/dt currents-requires short, low-inductance PCB trace. |
| VSW (11) | Switch Collector Node | High-voltage, high-current node connected to transformer primary; minimize trace length to reduce EMI. |
| VIN (12) | Main Supply Input | 3–20V input; requires ≥10µF local bypass; UVLO disables switching below 2.8V. |
| RCCOMP (13) | Load Compensation Filter | Accepts 0.1µF ceramic cap to ground; filters ripple for optional load compensation function. |
| ROCOMP (14) | Load Compensation Adjust | Optional external resistor (e.g., 12kΩ) compensates for secondary impedance effects on load regulation. |
| SHDN (15) | Shutdown Control | Active-low enable; pulls VC low and halts switching when <0.3V; draws only 15µA in shutdown. |
Key Features
| Feature | Design Value |
|---|---|
| Primary-side output voltage sensing | Eliminates optoisolator and third winding-reduces BOM count, cost, and board area in isolated flyback designs. |
| Resistor-programmable output voltage | Set via RFB/RREF ratio; achieves ±5% accuracy without user trimming or potentiometers. |
| Discontinuous mode regulation | Maintains stable output down to light loads (<20mA) via adaptive flyback amplifier timing and collapse detect. |
| Optional load compensation | ROCOMP/RCCOMP interface corrects for output impedance errors caused by diode VF, transformer ESR, and capacitor ESR. |
| External clock synchronization | SYNC pin accepts TTL/CMOS signals (10–90% duty cycle) to align switching frequency with system clocks or reduce beat frequencies. |
Applications
| Medical Isolated Power Supplies | Ethernet PoE Isolated Converters |
|---|---|
|
Use Scenario: Providing isolated ±9V rails for analog front-end instrumentation in patient-connected devices. IC Role / Device Role / Timing Role: Primary-side flyback controller managing isolation barrier integrity and meeting IEC 60601 creepage/clearance requirements. Use Value: Eliminates optoisolator aging and nonlinearities-ensuring long-term calibration stability and safety compliance without secondary-side components. |
Use Scenario: Generating isolated –9V output from 5V Ethernet PHY supply in IEEE 802.3af/at powered devices. IC Role / Device Role / Timing Role: High-efficiency flyback regulator delivering regulated negative rail across reinforced isolation barrier. Use Value: Achieves ±5% output accuracy without trimming-critical for biasing precision op-amps and ADC references in isolated signal chains. |
| Industrial Telecom Isolated DC/DC | Low-Power Isolated Sensor Interfaces |
|
Use Scenario: Converting 12V backplane supply to isolated 5V/–9V for RS-485 transceivers in harsh factory environments. IC Role / Device Role / Timing Role: Robust flyback controller with 125°C junction rating and 15µA shutdown current for extended standby operation. Use Value: Maintains regulation into discontinuous mode-supporting dynamic load changes from idle to full data transmission bursts. |
Use Scenario: Powering isolated current-loop sensors (4–20mA) with galvanic separation from host MCU. IC Role / Device Role / Timing Role: Compact, self-contained flyback controller enabling single-chip isolated bias generation. Use Value: Reduces component count by 4+ parts (opto + resistors + caps) while improving reliability and temperature stability over optocoupler-based solutions. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar isolated flyback controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| UCC28711DR | Fixed-frequency quasi-resonant controller; requires auxiliary winding for VOUT sensing; lower max input (28V). | Lacks primary-side sensing-needs third winding; better suited for higher-power (>10W) QR flyback with tighter efficiency targets. | Choose UCC28711DR if designing >8W supplies where QR topology improves efficiency, and third-winding layout is acceptable. |
| MAX17690ATP+ | Current-mode flyback controller with integrated 65V MOSFET; supports primary-side sensing but requires external shunt for current sense. | Higher breakdown voltage enables wider input ranges (up to 60V); lacks built-in load compensation circuitry. | Choose MAX17690ATP+ for 24V/48V industrial inputs where LT1425IS#PBF's 20V VIN limit is insufficient. |
Compared with UCC28711DR and MAX17690ATP+, the LT1425IS#PBF uniquely combines primary-side sensing, integrated 35V switch, and optional load compensation in a 16-pin SOIC-making it optimal for compact, cost-sensitive 3–20V input, ≤6W isolated supplies requiring ±5% accuracy without trimming.
Availability
LT1425IS#PBF is available at Aetrix Electronics and suitable for medical instrumentation, Ethernet isolated converters, and industrial telecom supplies requiring stable component supply with guaranteed long-term availability and lead-free compliance.
Supply support for LT1425IS#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, Inc. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving industrial, automotive, communications, and healthcare markets.
The LT1425IS#PBF belongs to Analog Devices' legacy Linear Technology isolated power controller family, engineered specifically for primary-side regulated flyback topologies in space-constrained, safety-critical applications.
FAQ
What is the maximum output power achievable with LT1425IS#PBF without external components?
The LT1425IS#PBF delivers up to 6W of isolated output power using only its internal 1.6A/35V switch, transformer, rectifier, and passive components. This assumes proper thermal design (θJA = 75°C/W), 285kHz operation, and ≤20V input. Exceeding 6W requires external MOSFETs and gate drivers-not supported by the LT1425IS#PBF architecture.
Does LT1425IS#PBF require an optoisolator or third winding for feedback?
No. The LT1425IS#PBF uses proprietary primary-side flyback pulse sensing to derive output voltage information directly from the VSW node-eliminating need for optoisolators, third windings, or secondary-side error amplifiers. This is confirmed in the device description, block diagram, and typical application circuits in the official datasheet.
How does LT1425IS#PBF maintain regulation at light loads?
The LT1425IS#PBF maintains regulation into discontinuous conduction mode via adaptive timing: a fixed enable delay (150ns), minimum enable time (180ns), and collapse-detect comparator ensure the flyback error amplifier activates only during valid portions of the flyback pulse-even at very low output currents (e.g., 20mA).
Can LT1425IS#PBF synchronize to an external clock, and what is the valid frequency range?
Yes. The SYNC pin on LT1425IS#PBF accepts logic-level signals (10–90% duty cycle) and supports synchronization from 320kHz to 450kHz. Minimum sync amplitude is 1.5V (typ), and input resistance is 40kΩ. Unused SYNC pins should be grounded for noise immunity.
What is the purpose of the ROCOMP and RCCOMP pins on LT1425IS#PBF?
The ROCOMP and RCCOMP pins implement optional load compensation: ROCOMP accepts an external resistor (e.g., 12kΩ) to inject correction current into the RFB node, while RCCOMP accepts a 0.1µF capacitor to filter ripple. Together, they compensate for output voltage droop caused by diode VF, transformer secondary ESR, and capacitor ESR-improving load regulation accuracy.
LT1425IS#PBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Active
- Function:
- Step-Up/Step-Down
- Output Configuration:
- Positive or Negative, Isolation Capable
- Topology:
- Flyback
- Output Type:
- -
- Number of Outputs:
- 1
- Voltage - Input (Min):
- 2.8V
- Voltage - Input (Max):
- 20V
- Voltage - Output (Min/Fixed):
- -
- Voltage - Output (Max):
- -
- Current - Output:
- 135mA (Switch)
- Frequency - Switching:
- 285kHz
- Synchronous Rectifier:
- No
- Operating Temperature:
- -40°C ~ 100°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 16-SO
LT1425IS#PBF FAQ
1.How can I place an order for LT1425IS#PBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1425IS#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 LT1425IS#PBF reliable?
The price and inventory of LT1425IS#PBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1425IS#PBF is usually 5 days.
3.What payment methods are accepted for LT1425IS#PBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1425IS#PBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1425IS#PBF?
LT1425IS#PBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1425IS#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 LT1425IS#PBF?
For technical support, including LT1425IS#PBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1425IS#PBF requirements.
6.How does Aetrix verify that LT1425IS#PBF is sourced from the original manufacturer or authorized distributors?
All LT1425IS#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 LT1425IS#PBF meets industry standards.
7.What is the process for return or replacement of LT1425IS#PBF?
All LT1425IS#PBF units undergo pre-shipment inspection (PSI). If there is an issue with LT1425IS#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 LT1425IS#PBF part is unused and in its original packaging.
Return procedure for LT1425IS#PBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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