MAX777

The MAX777 is pulse-skipping DC-DC converter that steps up from low-voltage inputs (1V guaranteed).It requires only three external components-an inductor (typically 22frH) and two capacitors.The MAX777 include an Active Rectifier TM that eliminates the need for an external catch diode, and permits regulation even when the input is greater than the output.  Also, unlike those in other step-up converters.

The MAX777 has the following features include:(1)1 V to 6.2V input guarantees start-up under load; (2)up to 240mA output; (3)load fully disconnected in shutdown; (4)82% efficiency; (5)output in regulation with input voltage above output voltage; (6)internal 1A power switch and active rectifier; (7)adjustable current limit allows low-cost inductors.The MAX777 combines a switch-mode regulator with an NPN bipolar switch, current limit, precision voltage reference, and active rectifier----all in a single monolithic device.In shutdown mode,the internal rectifier is completely turned off and disconnects the load from the source.

The absolute maximum ratings of the MAX777 are:(1)storage temperature range:-65 to +150°C;(2)lead temperature:+300°C;(3)supply voltage:0 to +7V;(4)reverse battery current:900mA.Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device.These are shess ratings only and functional operation of the device at these or any other conditions beyond those indicated in the operational secObns of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.The internal active rectifier of the MAX777 replaces the external Schottky catch diode in normal boost operation.The rectifier consists of a PNP pass transistor and a unique control circuit which, in shut-down mode, entirely disconnects the load from the source.This is a distinct advantage over standard boost topologies, since it prevents battery drain in shut-down.The primary factor in selecting both the output and input filter capacitor is low ESR. The ESR of both bypass and filter capacitors affects efficiency.Optimize performance by increasing filter capacitors or using specialized low-ESR capacitors.The smallest low-ESR SMT tantalum capacitors of MAX777 currently available are Sprague 595D or 695D series.