LTC1559-3.3/LTC1559-5
U
U
U
PIN FUNCTIONS
RESET (Pin 12): System Reset, Active High. This is a TTL-
compatible output driver. It can connect to systems that
require active high logic. The RESET output will go high if
RESET is pulled low.
LOBAT (Pin 9): Low Backup Battery Detector Output. This
is an open-drain output with an internal weak pull-up. It is
asserted if the NiCd cell terminal voltage drops below
1.0V. This pin is pulled high if the LTC1559 is in trickle
charge mode.
W
BLOCK DIAGRAM
P1
SW
V
BAK
V
/V
CC BAK
CHARGER
N1
CTL
BOOST/BACKUP
LOGIC
PS
+
–
BACKUP
RESET
RESET
LEVEL SENSE
AND DEBOUNCE
RESET
GENERATOR
V
REF
V
CC
V
REF
GAS GAUGE
+
–
–
+
LOBAT
UVLO
DETECTOR
THERMAL
LIMIT
BANDGAP
= 1.272V
SHUTDOWN
LOGIC
SHDN
V
REF
1559 BD
U
W
SWITCHING WAVEFORMS
Cold Power Boot-Up (Main Battery Replaced/Turned On)
Simplified LTC1559 Connections in a Battery Backup System
RATED BATTERY TERMINAL VOLTAGE
TO
SYSTEM
CONTROL
22µH
1
RESET
LTC1559
SW
1.2V
NiCd
RATED V VOLTAGE
CC
PS
V
CC
V
BAT
4
2
BACKUP
V
BAK
–5.5% (LTC1559-3.3)
3
–6% (LTC1559-5)
BACKUP
SYSTEM
PS
V
IN
V
OUT
V
CC
200ms
V
Q
CC
V
EXT
BAT
MAIN
MAIN SYSTEM
REGULATOR
C
OUT
BATTERY
RESET
1559 SW01
FOR MORE DETAILED CIRCUIT APPLICATION SCHEMATICS,
PLEASE REFER TO THE TYPICAL APPLICATIONS SECTION
BACKUP
1559 SW02
6
Linear [ Linear ]
