ST779
DESCRIPTION
The ST777/778/779 are dc-dc converters that step-up from low voltage inputs requiring only three external ponents, an inductor (typically 22µH) and two capacitors. The device include a Sinchronous Rectifier that eliminates the need for an external catch diode, and allows regulation even when the input is greater than the output. SCHEMATIC DIAGRAM
100µF
Unlike others step-up DC-DC converters the ST777/778/779’s Sinchronous Rectifier turns off in the shutdown mode, fully disconnecting the output from the source. This eliminates the current drain associated with conventional step-up converters when off or in shutdown. Supply current is 270µA under no load and only 20µA in stand by mode.
22µH
RLIM
DELAY TIMER
ILIM
ACTIVE RECTIFIER t OFF
SWITCH DRIVER
DELAY TIMER
OUT 6
100µF t ON
1 : N
RECTIFIER CONTROL
PGND 4
SEL 8
VREF
1.25V
7 SHDN
SHUTDOWN CONTROL
AGND 3
October 2002
1/11
ST777/778/779
ABSOLUTE MAXIMUM RATINGS
Symbol VCC LX OUT, SHDN...
