LT3781 - Bootstrap Start Dual Transistor Synchronous Forward Controller
Features
- High Voltage Operation up to 72V
- Synchronizable Operating Frequency and Output Switch Phase for Multiple Controller Systems
- Synchronous Switch Output
- Undervoltage Lockout Protection with 6V Hysteresis for Self-Biased Power
- Fixed Frequency Operation to 350kHz
- Local 1% Voltage Reference
- Input Overvoltage Protection
- Low Start-Up Current
- Programmable Start Inhibit for Power Supply Sequencing and Protection
- Optocoupler Support
- Soft-Start Control
Typical Application
Description
The LT3781 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 LT3781 is ideal for output derived power schemes, through the use of a large undervoltage lockout hysteresis range. The part is also equipped with an 18V VCC shunt regulator, which prevents exceeding absolute maximum ratings while in trickle start applications.
The LT3781’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 LT3781 is available in a 20-lead SSOP package.
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 |
|---|---|---|---|---|---|
| LT3781EG#PBF | SSOP-20 | G | E | 05-08-1640 (G20) | Yes |
| LT3781EG#TRPBF | SSOP-20 | G | E | 05-08-1640 (G20) | Yes |
| LT3781IG#PBF | SSOP-20 | G | I | 05-08-1640 (G20) | Yes |
| LT3781IG#TRPBF | SSOP-20 | G | I | 05-08-1640 (G20) | 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 | |
|---|---|---|---|---|---|---|
| LT3781EG#PBF | SSOP-20 | E | $7.14 | $4.95 | Yes | |
| LT3781EG#TRPBF | SSOP-20 | E | $5.05 | Yes | ||
| LT3781IG#PBF | SSOP-20 | I | $7.86 | $5.45 | Yes | |
| LT3781IG#TRPBF | SSOP-20 | I | $5.55 | 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.| Part Number | Description | Price | Documentation |
|---|---|---|---|
| DC448A | LT3710EFE LT3781EG LTC1698EGN | Dual Output Isolated Power Supply, 36V to 72V Input, 3.3Vout @ 10A, 1.8/2.5Vout @ 10A | Contact Factory | |
| DC467A | LT3781EG LTC1698EGN | Isolated Power Supply, 36V to 72V Input, 5Vout @ 30A | Contact Factory | |
| DC479A | LT3781EG, LTC1698EGN, LT1783CS5 | Isolated Synchronous, Forward Converter, Vin=36V-72V, Vout=3.3V @ 15A | $75.00 | |
| DC610A | LT3804EFE LT3781EG LTC1693-1IS8 | Dual Output Isolated Power Supply, 36V to 72V Input, +Vo1=3.3V @ 15A, +Vo2 = 1.8V @ 15A | $175.00 | |
| DC617A | LT3781EG LTC1698EGN LT1783CS5 | Isolated Synchronous Forward Converter, +Vin = 36V - 72V, +Vout = 2.5V @ 20A, Quarter Brick footprint | $75.00 | |
| Buy Now | |||
Applications
- Isolated Telecommunication Systems
- Personal Computers and Peripherals
- Distributed Power Step-Down Converters
- Lead Acid Battery Backup Systems
- Automotive and Heavy Equipment
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Design Tools
LTspice
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Models for the following parts are available in LTspice:
LT3781
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.
