Features and Benefits
- VIN and VOUT Limited Only by External Components
- Adjustable Slope Compensation
- Adjustable Overcurrent Protection with Automatic Restart
- Adjustable Operating Frequency (70kHz to 700kHz) with One External Resistor
- Synchronizable to an External Clock
- ±1.5% Reference Accuracy
- Current Mode Operation for Excellent Line and Load Transient Response
- RUN Pin with Precision Threshold and Adjustable Hysteresis
- Programmable Soft-Start with One External Capacitor
- Low Quiescent Current: 360μA
- Small 10-Lead MSOP and 3mm × 3mm DFN
The LTC3805 is a current mode controller for flyback DC/DC converters designed to drive an N-channel MOSFET in high input and output voltage converter applications. Operating frequency and slope compensation can be programmed by external resistors. Programmable overcurrent sensing protects the converter from short-circuits. Soft-start can be programmed using an external capacitor and the soft-start capacitor also programs an automatic restart feature.
The LTC3805 provides ±1.5% output voltage accuracy and consumes only 360μA of quiescent current during normal operation and only 40μA during micropower startup. Using a 9.5V internal shunt regulator, the LTC3805 can be powered from a high VIN through a resistor or it can be powered directly from a low impedance DC voltage of 9V or less.
The LTC3805 is available in the 10-lead MSOP package and the 3mm × 3mm DFN package.
|Turn On Voltage|
- Telecom Power Supplies
- 42V and 12V Automotive Power Supplies
- Isolated Electronic Equipment
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 (2)
Demonstration circuit 1311 is a Telecom isolated DC/DC converter featuring the LTC3805/-5 constant frequency current mode flyback controller. The DC1311 converts 18V to 72V input voltage to an isolated 3A of output current at 3.3V. The 300kHz constant frequency operation is maintained down to very light load to reduce low frequency noise generated over a wide range of load current. The converter provides high output voltage accuracy (typically ±2%) over wide load range with no minimum load requirement.
The DC1311 also provides non-isolated design by removing opto coupler and LTC4430 circuit. The demonstration circuit can be easily modified to generate different output voltages up to 15V. As output voltage is increased, the maximum output current must be reduced to limit the output power to no more than 10W.
Demonstration circuit 1045 is a Telecom isolated DC/DC converter featuring the LTC3805 constant frequency current mode flyback controller. The DC1045 converts 36V to 72V input voltage to an isolated 3A of output current at 3.3V. The 200kHz constant frequency operation is maintained down to very light load to reduce low frequency noise generated over a wide range of load current.
Documentation & Resources
R421 Reliability Data3/23/2018
Current Mode Flyback DC/DC Controller Provides Tremendous Design Flexibility3/1/2007 LT Journal
Tools & Simulations
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Models for the following parts are available in LTspice:
LTC3805 Companion Parts
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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.