Linear Technology Corporation introduces the LT3740, a high output power step-down synchronous controller that operates from very low input voltages without needing an auxiliary 5V gate drive supply. In addition to a DC/DC step-down controller, the LT3740 integrates a DC/DC step-up converter for generating its own MOSFET gate drive voltage. This function permits the use of inexpensive off-the-shelf 5V gate-drive N-channel MOSFETs, offering up to 3% higher efficiency than sub-logic gate-drive MOSFETs and eliminating the need for a secondary supply. The LT3740 is ideal for converting input supplies ranging from 2.2V to 22V to an output as low as 0.8V and at load currents from 2A to 20A with 93% typical efficiency. Applications include distributed power systems, point-of-load regulation and conversion of logic supplies. In particular, the LT3740 can step down from 5V, 3.3V and 2.5V rails.
The LT3740 operates at a fixed frequency of 300kHz and employs valley current mode control to deliver excellent transient response and very low on-times. In addition, the LT3740 uses low-side MOSFET current-sense architecture for current limiting and overload protection, eliminating the need for a sense resistor while improving efficiency. Three current limit threshold levels can be selected by connecting the range pin to ground, open or the input voltage. Furthermore, a power good signal is available to monitor the output voltage and the device has a tracking function that allows output voltage control during power up and power down.
The LT3740 is offered in a 16-lead 5mm x 3mm DFN package with an operating temperature range from -40°C to 85°C. Pricing starts at $1.95 each in 1,000-piece quantities.
Summary of Features: LT3740
Low Input Voltage: 2.2V
High Output Power - up to 20A
5V Drive for N-Channel MOSFETs Eliminates Auxiliary 5V Supply
Uses Standard 5V Logic-Level N-Channel MOSFETs
Valley Current Mode Control for Excellent Line and Load Regulation
No Sense Resistor Required (uses MOSFET RDS(ON) for Sensing)
Three Selectable Current Limit Levels
Power Good Signal and Tracking Function