LTC1558-3.3/LTC1558-5
Backup Battery Controller
with Programmable Output
FEATURES
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DESCRIPTION
The LTC
®
1558 is a backup battery controller that provides
all the functions necessary to implement a backup power
supply using a single NiCd cell. It includes a 1.2V boost
converter, an intelligent 2-stage battery charger, auto-
matic backup switching and a microprocessor reset gen-
erator. The boost converter uses a synchronous switching
architecture to achieve a typical efficiency of 70%, ensur-
ing maximum backup lifetime from a small NiCd cell.
The on-chip NiCd charger uses an internal gas gauge to
minimize fast recharge time and prevent overcharging of
the backup cell. The LTC1558 also provides a user pro-
grammable trickle charge current to compensate for self
discharge losses in the backup cell.
The LTC1558’s automatic backup switching architecture
requires minimum intervention from the host system and
provides feedback to the host to minimize system loading
in the backup state. Its internal V
CC
fault detector and reset
generator eliminate the need for a separate microproces-
sor supervisory chip in most applications.
The LTC1558 is available in an SO-8, 16-lead GN or SO
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Complete Battery Backup System in an
SO-8, 16-Pin GN or SO Package
Generates Adjustable Backup Voltage from a
Single 1.2V NiCd Button Cell
Automatic Main Supply to Backup Switching
Minimum 100mW Output Power
Automatic Fast Recharge of NiCd Battery
Programmable NiCd Trickle Charge Current
Smart NiCd Charger Minimizes Recharge Time and
Maximizes System Efficiency After Backup
On-Chip Power-On Reset
Pushbutton Reset Input
Reset Assertion Guaranteed at V
CC
= 1V
Short-Circuit Protection
Thermal Limiting
APPLICATIONS
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Notebook Computers
Palmtop Computers/PDAs
Portable Instruments
Battery-Powered Systems
TYPICAL APPLICATION
L1
22µH*
1.2V
NiCd
BACKUP
**BATTERY
+
C1
1µF
R1
14k
LTC1558-3.3
1
2
3
SW
GND
CTL
FB
V
BAK
V
CC
BACKUP
RESET
8
7
+
C2
0.1µF
R2
100k
RESET
S1
4
5
SYSTEM
µP
BACKUP TIME (MINUTES)
6
R3
220k
MAIN
BATTERY
4.5V TO 10V
Q1
Si4431DY
R4
221k
1%
R5
100k
1%
+
C
IN
100µF
16V
×2
LTC1435
†
SYNCHRONOUS
BUCK REGULATOR
*SUMIDA CD54-22µH
**SANYO CADNICA N-110AA
†
CONSULT LTC1435 DATA SHEET FOR
CIRCUIT APPLICATION INFORMATION
V
CC
3.3V
LOAD CURRENT
3A AT NORMAL MODE
30mA AT BACKUP MODE
1558 TA01
U
U
U
Backup Time
vs 3.3V Output Load Current
450
400
350
300
250
200
150
100
50
0
0
5
15
20
10
LOAD CURRENT (mA)
25
30
1558 TA02
V
CC
= 3.3V
V
BAK
= 3.78V
NiCd CELL
CAPACITY = 110mAHrs
1
LINER [ LINEAR TECHNOLOGY ]
