ST777 Datasheet, PDF (1/11 Pages) STMicroelectronics – LOW VOLTAGE INPUT, 3-3.3V/5V/ADJUSTABLE OUTPUT DC-DC CONVERTER WITH SYNCHRONOUS RECTIFIER

ST777/778/779
LOW VOLTAGE INPUT, 3-3.3V/5V/ADJUSTABLE OUTPUT
DC-DC CONVERTER WITH SYNCHRONOUS RECTIFIER
s 1V TO 6V INPUT GUARANTEES START-UP
UNDER LOAD
s MAXIMUM OUTPUT CURRENT OF 300mA
(778 OR 779 ADJUSTED TO 3V)
s LOAD FULLY DISCONNECTED IN
SHUTDOWN
s TYPICAL EFFICIENCY OF 82%
s INTERNAL 1A POWER SWITCH AND
SYNCHRONOUS RECTIFIER
s ADJUSTABLE CURRENT LIMIT ALLOWS
LOW-COST INDUCTORS
s SUPPLY CURRENT OF 270µA (NO LOAD)
s SHUTDOWN SUPPLY CURRENT 20µA
s PACKAGE AVAILABLE: DIP-8 AND SO-8
DIP-8
SO-8
DESCRIPTION
The ST777/778/779 are dc-dc converters that
step-up from low voltage inputs requiring only
three external components, 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
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.
VIN
DELAY
TIMER
tOFF
DELAY
TIMER
tON
22µH
100µF
RLIM
2
IN
15
ILIM LX
SWITCH
DRIVER
ACTIVE RECTIFIER _{OUT 6}
RECTIFIER
CONTROL
1:N
PGND 4
VO
100µF
7 SHDN
SHUTDOWN
CONTROL
1.25V
VREF
SEL 8
AGND
3
October 2002
1/11