High Efficiency Low Noise Synchronous Step-Down Switching Regulator

The LTC1435 is a synchronous step-down switching regulator controller that drives external N-channel power MOSFETs using a fixed frequency architecture. Burst Mode™ operation provides high efficiency at low load currents. A maximum duty cycle limit of 99% provides low dropout operation which extends operating time in battery-operated systems.

The operating frequency is set by an external capacitor allowing maximum flexibility in optimizing efficiency. A secondary winding feedback control pin, SFB, guarantees regulation regardless of load on the main output by forcing continuous operation. Burst Mode operation is inhibited when the SFB pin is pulled low which reduces noise and RF interference.

Soft start is provided by an external capacitor which can be used to properly sequence supplies. The operating current level is user-programmable via an external current sense resistor. Wide input supply range allows operation from 3.5V to 30V (36V maximum).

For a guaranteed and test minimum on-time refer to the LTC1435A, the "A" version of the LTC1435. The minimum on-time of the LTC1435A is guaranteed to be ≤300ns. The only difference between these two parts is this guaranteed minimum on-time. Pricing is the same.

Applications

* Notebook and Palmtop Computers, PDAs

* Cellular Telephones and Wireless Modems

* Portable Instruments

* Battery-Operated Devices

* DC Power Distribution Systems

* Dual N-Channel MOSFET Synchronous Drive

* Programmable Fixed Frequency

* Wide VIN Range: 3.5V to 36V Operation

* Ultrahigh Efficiency

* Very Low Dropout Operation: 99% Duty Cycle

* Low Standby Current

* Secondary Feedback Control

* Programmable Soft Start

* Remote Output Voltage Sense

* Logic Controlled Micropower Shutdown: IQ <25µA

* Foldback Current Limiting (Optional)

* Current Mode Operation for Excellent Line and Load Transient Response

* Output Voltages from 1.19V to 9V

* Available in 16-Lead Narrow SO and SSOP Packages