High Efficiency Low Noise Synchronous Step-Down Switching Regulators

The LTC1436A/LTC1437A are synchronous step-down switching regulator controllers that drive external N-channel power MOSFETs in a phase lockable, fixed frequency architecture. The Adaptive Power™ output stage selectively drives two N-channel MOSFETs at frequencies up to 400kHz while reducing switching losses to maintain high efficiencies at low output currents.

An auxiliary 0.5A linear regulator using an external PNP pass device provides a low noise, low dropout voltage source. A secondary winding feedback control pin (SFB) guarantees regulation regardless of the load on the main output by forcing continuous operation.

An additional comparator is available for use as a lowbattery detector. A power-on reset timer (POR) is included which generates a signal delayed by 65536/fCLK (300ms typically) after the output is within 5% of the regulated output voltage. Internal resistive dividers provide pin selectable output voltages with remote sense capability.

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).

Applications

* Notebook and Palmtop Computers, PDAs

* Cellular Telephones and Wireless Modems

* Portable Instruments

* Battery-Operated Devices

* DC Power Distribution Systems

* Maintains Constant Frequency at Low Output Currents

* Programmable Fixed Frequency (PLL Lockable)

* Wide VIN Range: 3.5V to 36V Operation

* Low Minimum On-Time (≤300ns) for High Frequency, Low Duty Cycle Applications

* Dual N-Channel MOSFET Synchronous Drive

* Very Low Dropout Operation: 99% Duty Cycle

* Low Dropout, 0.5A Linear Regulator for CPU I/O or Low Noise Audio Supplies

* Built-In Power-On Reset Timer

* Programmable Soft Start

* Low-Battery Detector

* Remote Output Voltage Sense

* Foldback Current Limiting (Optional)

* Pin Selectable Output Voltage

* Logic Controlled Micropower Shutdown: IQ < 25µA

* Output Voltages from 1.19V to 9V

* Available in 24-Lead Narrow SSOP and 28-Lead SSOP Packages