LTC1559-5_15 Datasheet, PDF (1/20 Pages) Linear Technology – Backup Battery Controller with Fixed Output

FEATURES
s _{Complete Battery Backup System in an SO-8,}
16-Pin GN or SO Package
s _{Generates Fixed Backup Voltage (3.07V/4.63V) 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 _{Onboard Power-Up and Push-Button Reset}
Generator
s _{Performs VCC Supervisory Functions}
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}
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTC1559-3.3/LTC1559-5
Backup Battery Controller
with Fixed Output
DESCRIPTION
The LTC^®1559 is a backup battery controller that provides
all the functions necessary to implement a backup 3.3V or
5V power supply using a single NiCd cell. It includes a 1.2V
to 3.07V/4.63V boost converter, an intelligent 2-stage
battery charger, automatic backup switching and a micro-
processor reset generator. The boost converter uses a
synchronous switching architecture to achieve a typical
efficiency of 70%, ensuring 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, thereby improving system efficiency and
extending the life of the backup cell. The LTC1559 also
provides a user programmable trickle charge current to
compensate for self-discharge losses in the backup cell.
The LTC1559’s automatic backup switching scheme
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 LTC1559 is available in an SO-8, 16-pin GN or SO
package.
TYPICAL APPLICATION
**BACKUP
BATTERY
1.2V
NiCd
+ _C1
1µF
S1
RESET
*L1
22µH
R1
18
68k
2
SW
GND
V_BAK
V_CC
7
+
3
CTL
LTC1559-3.3
6
BACKUP
4 _PS
RESET ⁵
C2
1µF
R2
100k
SYSTEM
µP
MAIN
BATTERY
4.5V TO 28V
†_LTC1435
SYNCHRONOUS
BUCK
REGULATOR
Q1
P-MOSFET
V_OUT
Si9424DY
3.3V AT NORMAL MODE
C3
100µF
10V
* SUMIDA CD54-22µH 3A
** PANASONIC P-11AAH
V_BAK
33mA (3.07V) AT BACKUP MODE
† CONSULT LTC1435 DATA SHEET FOR
>33mA (3.3V) AT NORMAL MODE
APPLICATION CIRCUIT INFORMATION
1559 TA01
Backup Time vs
V_BAK Output Load Current
800
V_BAK = 3.07V
700
NiCd CELL = P-11AAH
(110mA Hrs)
600
500
400
300
200
100
0
05
10 15 20 25 30 35
V_BAK LOAD CURRENT (mA)
1559 TA02
1