SC1537

700mA SmartLDO TM SC1537 PRELIMINARY - July 25, 2000 TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com DESCRIPTION The SC1537 is designed to maintain a glitch-free 3.3V output when at least one of two inputs, 5V (VIN) and 3.3V (VAUX), is present. Whenever VIN exceeds a predetermined threshold value, the internal 3.3V linear regulator is enabled, and DR is pulled high. When VIN falls below a lower threshold value, DR is pulled low and the internal linear regulator is turned off. DR has been designed to drive the gate of an external low threshold P-channel MOSFET, which can be used to connect the 3.3V supply directly to the regulator output. This ensures an uninterrupted 3.3V output even if VIN falls out of specification. A maximum RDS(ON) of 100mΩ is recommended. When both supplies are simultaneously available, the drive pin (DR) will be pulled High, turning off the external PMOS switch. The internal 5V detector has its upper threshold (for VIN rising) set to 4.22V (typical) while the lower threshold (for VIN falling) is at 4.05V (typical) giving a hysteresis of approximately 170mV. The SC1537 is available in the popular SO-8 and 5-lead TO-263 surface mount packages. Q1 FEATURES = = = = = = = Glitch-free transition between input sources Internal logic selects input source Gate drive for external PMOS bypass switch 5V detector with hysteresis 1% regulated output voltage accuracy 700mA load current capability SO-8 and TO-263 packages APPLICATIONS = = ...