Constant Frequency Step-Down DC/DC Controller with LDO Regulator

The LTC3700 is a constant frequency current mode stepdown (buck) DC/DC controller with excellent AC and DC load and line regulation. The on-chip 150mA low dropout (LDO) linear regulator can be powered from the buck controller’s input supply, its own independent input supply or the buck regulator’s output. The buck controller incorporates an undervoltage lockout feature that shuts down the controller when the input voltage falls below 2.1V.

The buck regulator provides a ±2.5% output voltage accuracy. It consumes only 210µA of quiescent current in normal operation with the LDO consuming an additional 50µA. In shutdown, a mere 10µA (combined) is consumed.

For applications where efficiency is a prime consideration, the buck controller is configured for Burst Mode operation which enhances efficiency at low output current. To further maximize the life of a battery source, the external P-channel MOSFET is turned on continuously in dropout (100% duty cycle). High constant operating frequency of 550kHz allows the use of a small external inductor.

The LDO is protected by both current limit and thermal shutdown circuits.

The LTC3700 is available in a tiny 10-pin MSOP.

Applications

* Notebook Computers

* Portable Instruments

* One or Two Li-Ion Battery-Powered Applications

* Dual Output Regulator in Tiny 10-Pin MSOP

* High Efficiency: Up to 94%

* Wide VIN Range: 2.65V to 9.8V

* Constant Frequency 550kHz Operation

* 150mA LDO Regulator with Current Limit and Thermal Shutdown Protection

* High Output Currents Easily Achieved

* Burst Mode® Operation at Light Load

* Low Dropout: 100% Duty Cycle

* Current Mode Operation for Excellent Line and Load Transient Response

* 0.8V Reference Allows Low Output Voltages

* Low Quiescent Current: 260µA Total

* Shutdown Mode Draws Only 10µA Supply Current

* Common Power Good Output for Both Supplies