LTC1558-5_15 Datasheet, PDF (1/20 Pages) Linear Technology – Backup Battery Controller with Programmable Output

LTC1558-3.3/LTC1558-5
Backup Battery Controller
with Programmable Output
FEATURES
s _{Complete Battery Backup System in an}
SO-8, 16-Pin GN or SO Package
s _{Generates Adjustable Backup Voltage from a}
Single 1.2V NiCd Button Cell
s _{Automatic Main Supply to Backup Switching}
s _{Minimum 100mW Output Power}
s _{Automatic Fast Recharge of NiCd Battery}
s _{Programmable NiCd Trickle Charge Current}
s _{Smart NiCd Charger Minimizes Recharge Time and}
Maximizes System Efficiency After Backup
s _{On-Chip Power-On Reset}
s _{Pushbutton Reset Input}
s _{Reset Assertion Guaranteed at VCC = 1V}
s _{Short-Circuit Protection}
s _{Thermal Limiting}
U
APPLICATIONS
s _{Notebook Computers}
s _{Palmtop Computers/PDAs}
s _{Portable Instruments}
s _{Battery-Powered Systems}
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.
TYPICAL APPLICATION
1.2V
NiCd
BACKUP
**BATTERY
+
C1
1µF
RESET
S1
L1
22µH*
LTC1558-3.3
R1
14k
1 _SW
V_BAK ⁸
2
GND
V_CC ⁷
3
6
CTL BACKUP
4
FB
5
RESET
+ _C2
R2
0.1µF 100k
SYSTEM
µP
MAIN
BATTERY
4.5V TO 10V
Q1
Si4431DY
R3
220k
R4 ⁺
221k
1%
R5
100k
1%
C_IN
100µF
16V
×2
LTC1435^†
V_CC
3.3V
SYNCHRONOUS
BUCK REGULATOR
*SUMIDA CD54-22µH
**SANYO CADNICA N-110AA
†_{CONSULT LTC1435 DATA SHEET FOR}
CIRCUIT APPLICATION INFORMATION
LOAD CURRENT
3A AT NORMAL MODE
30mA AT BACKUP MODE
1558 TA01
Backup Time
vs 3.3V Output Load Current
450
V_CC = 3.3V
400
V_BAK = 3.78V
NiCd CELL
350
CAPACITY = 110mAHrs
300
250
200
150
100
50
0
0
5 10 15 20 25 30
LOAD CURRENT (mA)
1558 TA02
1