LT1681 - Dual Transistor Synchronous Forward Controller
Features
- High Voltage: Operation Up to 72V
- Synchronizable Operating Frequency and Output Switch Phase for Multiple Controller Systems
- Fixed Frequency Operation to 350kHz
- Adaptive and Adjustable Blanking
- Synchronous Rectifier Driver
- Local 1% Voltage Reference
- Undervoltage Lockout Protection with Hysteresis
- Input Overvoltage Protection
- Programmable Start Inhibit
- Transformer Primary Saturation Protection
- Optocoupler Feedback Support
- Soft-Start Control
Typical Application
Description
The LT1681 controller simplifies the design of high power synchronous dual transistor forward DC/DC converters. The part employs fixed frequency current mode control and supports both isolated and nonisolated topologies. The IC drives external N-channel power MOSFETs and operates with input voltages up to 72V.
The LT1681’s operating frequency is programmable and can be synchronized up to 350kHz. Switch phase is also controlled during synchronized operation to accommodate multiple converter systems. Internal logic guarantees 50%maximum duty cycle operation to prevent transformer saturation.
The LT1681 incorporates a soft-start feature that provides a controlled increase in supplied current during start-up and after an undervoltage lockout or overvoltage/overcurrent event.
The part is available in a 20-lead wide SO package to support high voltage pin-to-pin clearance.
Packaging
CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.
For complete and up to date package information and drawings, please refer to our packaging page
| Part Number | Package | Code | Temp | Package Drawing |
RoHS |
|---|---|---|---|---|---|
| LT1681ESW#PBF | SW-20 | SW | E | 05-08-1620 (SW20) | Yes |
| LT1681ESW#TRPBF | SW-20 | SW | E | 05-08-1620 (SW20) | Yes |
| LT1681ISW#PBF | SW-20 | SW | I | 05-08-1620 (SW20) | Yes |
| LT1681ISW#TRPBF | SW-20 | SW | I | 05-08-1620 (SW20) | Yes |
Order Info
- Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
- Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
- Please refer to our general ordering information or the product datasheet for more details
Package Variations and Pricing
| Part Number | Package | Temp | Price (1-99) |
Price (1k)* |
RoHS | |
|---|---|---|---|---|---|---|
| LT1681ESW#PBF | SW-20 | E | $5.92 | $5.00 | Yes | |
| LT1681ESW#TRPBF | SW-20 | E | $5.10 | Yes | ||
| LT1681ISW#PBF | SW-20 | I | $6.51 | $5.50 | Yes | |
| LT1681ISW#TRPBF | SW-20 | I | $5.60 | Yes | ||
| Buy Now • Request Samples | ||||||
Demo Boards
Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.Click here to view our complete list of demo boards
Applications
- Isolated Telecommunication Systems
- Personal Computers and Peripherals
- Lead Acid Battery Backup Systems
- Automotive and Heavy Equipment
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Design Tools
LTspice
LTspice® software is a powerful, fast and free simulation tool, schematic capture and waveform viewer with enhancements and models for improving the simulation of switching regulators. Click here to download LTspice
Models for the following parts are available in LTspice:
LT1681
Technical Support
- For immediate technical assistance, contact your local sales office or distributor or call 1-800-4-LINEAR (US customers only) or 408-432-1900.
- For less urgent requests, please complete our Technical Support Request Form. Please allow 2-3 business days for reply.
