MAX1534

19-2662; Rev 0; 10/02 High-Efficiency, Triple-Output, Keep-Alive Power Supply for Notebook Computers General Description The MAX1534 is a high-efficiency, triple-output power supply for keep-alive (always on) voltage rails. The 500mA buck regulator with an internal current-limited 0.5Ω PMOS steps down the battery or wall adapter supply rail to a fixed 5V or an adjustable output voltage. Two integrated low-voltage linear regulators follow this output and provide two independent preset output voltages of 3.3V and 1.8V, or adjustable output voltages. The buck regulator utilizes a peak current-limit, pulsefrequency modulation (PFM) architecture for highest light-load efficiency to conserve battery life. High switching frequencies (up to 200kHz) allow the use of tiny surface-mount inductors and output capacitors. Operation to 100% duty cycle minimizes dropout voltage (250mV at 500mA). The low-dropout linear regulators use an internal P-channel metal-oxide (PMOS) pass transistor to minimize supply current and deliver up to 160mA each of continuous current. The MAX1534 includes a power-OK (POK) signal that indicates all outputs are in regulation. The 4% accurate threshold of the SHDN input permits its use as a lowbattery detector. The MAX1534 is available in a small 16-pin thin QFN (4mm ✕ 4mm) package, occupying 33% less board space than discrete solutions. Features o One Switching and Two Linear Regulators o Switching Regulator +4.5V to +24V Input Voltage Range Over 95% Efficienc...