LTC1437

Features:

n Maintains Constant Frequency at Low Output Currents
n Dual N-Channel MOSFET Synchronous Drive
n Programmable Fixed Frequency (PLL Lockable)
n Wide V_IN Range: 3.5V to 36V Operation
n Ultrahigh Efficiency
n Very Low Dropout Operation: 99% Duty Cycle
n Low Dropout, 0.5A Linear Regulator for VPP Generation or Low Noise Audio Supply
n Built-In Power-On Reset Timer
n Programmable Soft Start
n Low-Battery Detector
n Remote Output Voltage Sense
n Foldback Current Limiting (Optional)
n Pin Selectable Output Voltage
n Logic Controlled Micropower Shutdown: I_Q < 25A
n Output Voltages from 1.19V to 9V
n Available in 24-Lead Narrow SSOP and 28-Lead SSOP Packages


Application

Notebook and Palmtop Computers, PDAs
Cellular Telephones and Wireless Modems
Portable Instruments
Battery-Operated Devices
DC Power Distribution Systems


Pinout

Specifications

Input Supply Voltage (V_IN).................................................. 36V to 0.3V
Topside Driver Supply Voltage (Boost) ............................... 42V to 0.3V
Switch Voltage (SW)............................................................ V_IN + 5V to 5V
EXTV_CC Voltage .................................................................. 10V to 0.3V
POR, LBO Voltages .............................................................. 12V to 0.3V
AUXFB Voltage .................................................................... 20V to 0.3V
AUXDR Voltage..................................................................... 28V to 0.3V
SENSE⁺, SENSE,V_OSENSE Voltages..................................... INTV_CC + 0.3V to 0.3V
V_PROG Voltage..................................................................... INTV_CC to 0.3V
PLL LPF, I_TH Voltages ......................................................... 2.7V to 0.3V
AUXON, PLLIN, SFB,RUN/SS, LBI Voltages .......................... 10V to 0.3V
Peak Driver Output Current < 10s (TGL, BG)..................... 2A
Peak Driver Output Current < 10s (TGS) .......................... 250mA
INTV_CC Output Current ...................................................... 50mA
Operating Temperature Range
    LTC143XC ...................................................................... 0°C to 70°C
    LTC143XI ....................................................................... 40°C to 85°C
Junction Temperature (Note 1) .......................................... 125°C
Storage Temperature Range ............................................. 65°C to 150°C
Lead Temperature (Soldering, 10 sec)............................... 300°C


Description

The LTC^®1436/LTC1437 are synchronous step-down switching regulator controllers which drive external N-channel power MOSFETs in a phase lockable, fixed frequency architecture. The Adaptive Power^TM 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 load on the main output by forcing continuous operation.

An additional comparator of The LTC1436/LTC1437  is available for use as a lowbattery detector. A power-on reset timer (POR) is included which generates a signal delayed by 65536/f_CLK (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 of The LTC1436/LTC1437  is user-programmable via an external current sense resistor. Wide input supply range allows operation from 3.5V to 30V (36V maximum).