SC1578

HIGH-EFFICIENCY STEP-DOWN DC-DC CONVERTER January 29, 1998 SC1578 TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com DESCRIPTION The SC1578 is a high performance step-down DC-DC converter, designed to drive an external P-channel MOSFET to generate programmable output voltages. Two main schemes of pulse-skipping and pulsefrequency modulation are employed to maintain low quiescent current and high conversion efficiency over wide ranges of input voltage and loads. The SC1578 delivers 10mA to 2A of output current with 87%-93% efficiency at VIN=9V, VOUT=5V. A current sense comparator with both inverting and non-inverting inputs uncommitted is included to provide the crucial function of either current limit protection or constant output current control. When the SC1578 is used in a highside current sensing step-down constant current source, the efficiency is typically greater than 90%. Duty cycle can be adjusted to greater than 90% by connecting a resistor from the DUTY pin to VIN. Quiescent current is about 90µA and can be reduced to 8µA in shutdown mode. With a switching frequency range of 90kHz to 280kHz, small size switching components may be used, which is ideal for battery powered portable equipment. FEATURES 4V to 24V input voltage operation. High efficiency (up to 95%). Low quiescent current at 90µA. Pulse-skipping and pulse-frequency modulation. Inputs-uncommitted current sense comparator. Duty cycle adjustable 90kHz to 280kHz oscillator frequen...