LT3825

PRODUCTION

Isolated No-Opto Synchronous Flyback Controller with Wide Input Supply Range

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Overview

  • Senses Output Voltage Directly from Primary Side Winding—No Opto-Isolator Required
  • Synchronous Driver for High Efficiency
  • Input Voltage Limited Only by External Power Components
  • Accurate Output Regulation without User Trims
  • Switching Frequency from 50kHz to 250kHz
  • Synchronizable
  • Load Compensation
  • Programmable Undervoltage Lockout
  • Available in a Thermally Enhanced 16-Lead TSSOP Package

The LT3825 is an isolated switching regulator controller designed for medium power flyback topologies. A typical application is 10W to 60W with input voltage limited only by external power path components. A third transformer winding provides output voltage feedback.

The LT3825 is a current mode controller that regulates output voltage based on sensing secondary voltage via a transformer winding during flyback. This allows for tight output regulation without the use of an opto-isolator, improving dynamic response and reliability. Synchronous rectification increases converter efficiency and improves output cross regulation in multiple output converters.

The LT3825 operates in forced continuous conduction mode which improves cross regulation in multiple winding applications. Switching frequency is user programmable and can be externally synchronized. The part also has load compensation, undervoltage lockout and soft-start circuity.

Applications

  • Isolated Medium Power (10W to 60W) Supplies
  • Isolated Telecom, Medical Converters
  • Instrumentation Power Supplies
  • Isolated Power over Ethernet Supplies
LT3825
Isolated No-Opto Synchronous Flyback Controller with Wide Input Supply Range
48V to 3.3V at 12A Isolated Supply Efficiency Product Package 1 Regulation
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Documentation

Data Sheet 1

Reliability Data 1

User Guide 6

Design Note 1

Technical Articles 2

Data Sheet

This is the most up-to-date revision of the Data Sheet.

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Software Resources

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Hardware Ecosystem

Parts Product Life Cycle Description
Oscillators 1
LTC6909
PRODUCTION 1 to 8 Output, Multiphase Silicon Oscillator with Spread Spectrum Modulation
Switching Regulators & Controllers 2
LTM8047
RECOMMENDED FOR NEW DESIGNS 3.1VIN to 32VIN Isolated μModule (Power Module) DC/DC Converter
LTM8048
RECOMMENDED FOR NEW DESIGNS 3.1VIN to 32VIN Isolated μModule (Power Module) DC/DC Converter with LDO Post Regulator
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Tools & Simulations

LTspice 1

Models for the following parts are available in LTspice:

  • LT3825
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.

Evaluation Kits

eval board
schematic 1
DC894C-B

LT3825EFE Isolated Demo Board | Synchronous Flyback Controller, 36V ≤ VIN ≤ 72V; VOUT = 5V @ 8A

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Product Details

Demonstration circuit 894C-B is a 36V-72Vin, synchronous flyback converter featuring the LT3825. The circuit was designed specifically to attain a high current, low ripple, synchronously rectified flyback to efficiently power 5.0V loads at up to 8A from a typical telecom input voltage range.

eval board
schematic 2
DC894B-C

LT3825EFE Demo Board | Isolated, 36V ≤ VIN ≤ 72V, VOUT = 12V @ 5A

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Product Details

Demonstration circuit 894B-C is a 36V-72Vin, synchronous flyback converter featuring the LT3825. This circuit was designed specifically to attain a high current, low ripple, synchronously rectified flyback to efficiently power 12V loads at up to 5A from a typical telecom input voltage range. This circuit features synchronous rectifier drive outputs, output voltage regulation without the need of an optocoupler, self-starting architecture and input undervoltage lockout.

eval board
schematic 3
DC894C-C

LT3825EFE Isolated Demo Board | Synchronous No Opto Flyback Controller, 36V ≤ VIN ≤ 72V; VOUT = 12V @ 5A

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Product Details

Demonstration circuit 894C-C is a 36V-72VIN, synchronous flyback converter featuring the LT3825. This circuit was designed specifically to attain a high current, low ripple, synchronously rectified flyback to efficiently power 12V loads at up to 5A from a typical telecom input voltage range. This circuit features synchronous rectifier drive outputs, output voltage regulation without the need of an optocoupler, self-starting architecture and input undervoltage lockout.

eval board
schematic 4
DC894A-A

LT3825EFE Demo Board I Synchronous Flyback Converter, VIN = 36V to 72V, VOUT = 3.3V @ 12A

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Product Details

Demonstration circuit 894A-A is a 36V-72VIN, synchronous flyback converter featuring the LT3825. This circuit was designed specifically to attain a high current, low ripple, synchronously rectified flyback to efficiently power 3.3V loads at up to 12A from a typical telecom input voltage range. This circuit features synchronous rectifier drive outputs, output voltage regulation without the need of an optocoupler, a self-starting architecture and input undervoltage lockout.

eval board
schematic 5
DC950A-A

LT3825EFE Demo Board | Isolated Synchronous Flyback, 36V ≤ VIN ≤ 72V, VOUT: 5V/2A, 3.3V/3A, 2.5V/3A

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Product Details

Demonstration circuit 950A-A is an isolated, 30W multi-output, synchronous flyback converter in 1/8 brick format featuring the LT3825. Output voltage sensing is implemented without the use of opto-coupler, by sensing the voltage across a primary side auxiliary winding. A load compensation circuit is used to compensate for voltage drops caused by load currents. DC950A-A has input voltage range 36V-72V and features the LT3825. Demonstration circuit 950A uses a transformer design with tapped secondary winding, to achieve higher efficiency and better cross regulation than is possible with a transformer that uses a separate winding for each output.



eval board
schematic 6
DC1143A

LT3825EFE Demo Board | Synchronous Isolated Flyback, 36V ≤ VIN ≤ 72V, VOUT: 3.3V @ 6A

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Product Details

Demonstration circuit 1143 is a 20W isolated flyback converter with synchronous rectification and primary-side regulation featuring the LT3825. The circuit was designed to demonstrate the high levels of performance, efficiency and small solution size attainable using this part in a flyback power supply. It operates at 250kHz and produces a regulated 3.3V, 6A output from an input voltage range of 36V to 72V: suitable for telecom and other applications. It has a footprint area that is 1.0 inch square. Synchronous rectification helps to attain efficiency exceeding 88%. Isolation voltage is 1500VDC.



DC894C-B
LT3825EFE Isolated Demo Board | Synchronous Flyback Controller, 36V ≤ VIN ≤ 72V; VOUT = 5V @ 8A
DC894C - Schematic
DC894B-C
LT3825EFE Demo Board | Isolated, 36V ≤ VIN ≤ 72V, VOUT = 12V @ 5A
DC894B-B - Schematic
DC894C-C
LT3825EFE Isolated Demo Board | Synchronous No Opto Flyback Controller, 36V ≤ VIN ≤ 72V; VOUT = 12V @ 5A
DC894C - Schematic
DC894A-A
LT3825EFE Demo Board I Synchronous Flyback Converter, VIN = 36V to 72V, VOUT = 3.3V @ 12A
DC894A-A - Schematic
DC950A-A
LT3825EFE Demo Board | Isolated Synchronous Flyback, 36V ≤ VIN ≤ 72V, VOUT: 5V/2A, 3.3V/3A, 2.5V/3A
DC950A-A - Schematic
DC1143A
LT3825EFE Demo Board | Synchronous Isolated Flyback, 36V ≤ VIN ≤ 72V, VOUT: 3.3V @ 6A
DC1143A - Schematic

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