Overview
Features and Benefits
- Drives External Power MOSFET with External ISENSE Resistor
- Application Input Voltage Limited Only by External Power Components
- Senses Output Voltage Directly from Primary Side Winding—No Optoisolator Required
- Accurate Regulation Without User Trims
- Regulation Maintained Well into Discontinuous Mode
- Switching Frequency from 50kHz to 250kHz with External Capacitor
- Optional Load Compensation
- Optional Undervoltage Lockout
- Available in 16-Pin SO and SSOP Packages
Product Details
The LT1725 is a monolithic switching regulator controller specifically designed for the isolated flyback topology. It drives the gate of an external MOSFET and is generally powered from a third transformer winding. These features allow for an application input voltage limited only by external power path components. The third transformer winding also provides output voltage feedback information, such that an optoisolator is not required. Its gate drive capability coupled with a suitable external MOSFET can deliver load power up to tens of watts.
The LT1725 has a number of features not found on most other switching regulator ICs. By utilizing current mode switching techniques, it provides excellent AC and DC line regulation. Its unique control circuitry can maintain regulation well into discontinuous mode in most applications. Optional load compensation circuitry allows for improved load regulation. An optional undervoltage lockout pin halts operation when the application input voltage is too low. An optional external capacitor implements a soft-start function. A 3V output is available at up to several mA for powering primary side application circuitry.
Applications
- Telecom Isolated Converters
- Offline Isolated Power Supplies
- Instrumentation Power Supplies
Product Categories
Product Lifecycle
Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Evaluation Kits (8)
Documentation & Resources
-
R387 Reliability Data3/26/2018
-
DC37*A - Demo Manual3/19/2010
-
DC526A-A - Demo Manual12/7/2009
-
DC562A-C - Demo Manual12/7/2009
-
DC562A-B - Demo Manual12/7/2009
-
DC638A - Demo Manual9/24/2009
-
DC508A - Demo Manual9/24/2009
-
DC431A - Demo Manual9/24/2009
-
Simple Isolated Telecom Flyback Circuit Provides Regulation Without Optocoupler5/1/2002 LT Journal
Tools & Simulations
LTspice
LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.

Models for the following parts are available in LTspice:
Product Recommendations
LT1725 Companion Parts
Design Resources
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.View our quality and reliability program and certifications for more information.
Part Number | Material Declaration | Reliability Data | Pin/Package Drawing | CAD Symbols, Footprints & 3D Models |
---|---|---|---|---|
LT1725CGN#PBF | Material Declaration | Reliability Data | 16-Lead SSOP (Narrow 0.15 Inch) | |
LT1725CGN#TRPBF | Material Declaration | Reliability Data | 16-Lead SSOP (Narrow 0.15 Inch) | |
LT1725CS#PBF | Material Declaration | Reliability Data | 16-Lead SOIC (Narrow 0.15 Inch) | |
LT1725CS#TRPBF | Material Declaration | Reliability Data | 16-Lead SOIC (Narrow 0.15 Inch) | |
LT1725IGN#PBF | Material Declaration | Reliability Data | 16-Lead SSOP (Narrow 0.15 Inch) | |
LT1725IGN#TRPBF | Material Declaration | Reliability Data | 16-Lead SSOP (Narrow 0.15 Inch) | |
LT1725IS#PBF | Material Declaration | Reliability Data | 16-Lead SOIC (Narrow 0.15 Inch) | |
LT1725IS#TRPBF | Material Declaration | Reliability Data | 16-Lead SOIC (Narrow 0.15 Inch) | |
Wafer Fabrication Data | R387 Reliability Data |
PCN-PDN Information
Select a model from the dropdown below to subscribe to PCN/PDN notifications and view past notifications as well.
Support & Discussions
Sample & Buy
Ordering FAQs
See our Ordering FAQs for answers to questions about online orders, payment options and more.
Buy Now Pricing
(**) Displayed Buy Now Price and Price Range is based on small quantity orders.
List Pricing
(*)The 1Ku list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Analog Devices, Inc. authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.
Lead Times
Please see the latest communication from our CCO regarding lead times.
Sampling
A Sample link will be shown above, next to the part, only for parts that are included in our sample program. Selecting the Sample button will redirect to the third-party ADI Sample Site. The part selected will carry over to your cart on this site once logged in. Please create a new account there if you have never used the site before. Contact SampleSupport@analog.com with any questions regarding this Sample Site.
Evaluation Boards
Pricing displayed is based on 1-piece.
Up to two boards can be purchased through Analog.com. To order more than two, please purchase through one of our listed distributors.
Pricing displayed is based on 1-piece. The USA list pricing shown is for budgetary use only, shown in United States dollars (FOB USA per unit), and is subject to change. International prices may vary due to local duties, taxes, fees and exchange rates.