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
s
s
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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
LTC1558-3.3/LTC1558-5
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
Terminal Voltages
V
CC ..........................................................................................
6V
V
BAK
, BACKUP ..................................................... 12V
SW ...................................................................... 14V
All Other Pins .................................. – 0.3V to V
CC
+ 0.3V
Input Currents (SW) ........................................... 500mA
PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
TOP VIEW
SW 1
GND 2
CTL 3
FB 4
8 V
BAK
7 V
CC
6 BACKUP
5 RESET
TOP VIEW
SW 1
SW 2
PGND 3
GND 4
CTL 5
SHDN 6
16 V
BAK
15 V
BAK
14 V
CC
13 BACKUP
12 RESET
11 RESET
10 NC
9
LOBAT
LTC1558CS8-3.3
LTC1558CS8-5
S8 PART MARKING
155833
15585
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 130°C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
CC
V
BAT
V
REF
I
VCC
I
BAT
PARAMETER
Operating Voltage Range
Backup Battery Cell Voltage
Internal Reference Voltage
Quiescent Supply Current (Note 2)
Peak Inductor Current (Backup Mode)
Battery Backup Switching
V
BAT
= 1.2V, T
A
= 0°C to 70°C unless otherwise noted.
MIN
q
q
q
q
q
CONDITIONS
LTC1558-3.3
LTC1558-5
Boost Converter in Low Current Mode (Note 7)
Boost Converter in High Current Mode (Note 7)
V
CC
= 0V
Voltage at V
FB
Relative to V
REF
Voltage at V
FB
Relative to V
REF
Voltage at V
FB
Relative to V
REF
Voltage at V
FB
Relative to V
REF
I
BAT(SHDN)
Battery Standby Current
I
VCC(SHDN)
Supply Current During Shutdown (Note 3)
V
BAK(ON)
V
BST(ON)
V
BAK(OFF)
V
BST(OFF)
V
LOBAT
Backup Request Trip Point
Boost Converter Assertion Trip Point
Backup Deassertion Trip Point
Boost Converter Deassertion Trip Point
Low V
BAT
Detect (Note 3)
2
U
U
W
W W
U
W
V
BAK
Output Current ................... Short-Circuit Protected
Operating Ambient Temperature Range ....... 0°C to 70°C
Junction Temperature .......................................... 125°C
Storage Temperature Range .................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
ORDER PART
NUMBER
LTC1558CGN-3.3
LTC1558CGN-5
LTC1558CS-3.3
LTC1558CS-5
FB 7
NC 8
GN PACKAGE
S PACKAGE
16-LEAD PLASTIC SSOP 16-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 110°C/ W (GN)
T
JMAX
= 125°C,
θ
JA
= 110°C/ W (S)
TYP
MAX
3.465
5.250
UNITS
V
V
V
V
µA
mA
mA
µA
µA
%
%
%
%
V
2.90
4.40
1.0
1.247
80
225
1.2
1.272
155
165
330
0.1
– 10.5
– 10.5
–9
– 10.5
0.95
– 7.5
– 7.5
–6
– 7.5
1
1.5
1.297
250
225
445
15
50
– 5.5
– 5.5
–4
– 5.5
1.05
q
q
q
q
q
q
q
q
q
LTC1558-3.3/LTC1558-5
ELECTRICAL CHARACTERISTICS
SYMBOL
V
UVLO(ON)
V
UVLO(OFF)
V
LOBAT
I
CHGF
I
CHGT
Q
RECH
Q
TRK
V
CTL(CLAMP)
V
CTL
t
CTL
Reset Timer
t
HRESET
t
RST
V
RST1
V
RST
I
SC
Pushbutton Duration for Hard Reset
RESET Pulse Width
RESET Output Voltage
RESET Output Voltage
RESET Output Current
Short-Circuit Current
Internal V
CC
Monitor Comparator
t
PLH
V
UVLO(ON)
Comparator Propagation
Delay (Rising)
SHDN Input Threshold
SHDN Pin Bias Current
FB Pin Bias Current
∆V
CC
= – (9% V
CC
+ 300mV), V
OD
= 300mV
9
µs
V
CTL
Low for < t
HRESET
(Soft Reset)
V
CTL
Low for > t
HRESET
(Hard Reset)
V
CC
= 1V, I
SINK
= 10µA
V
CC
= 4.25V, I
SINK
= 1.6mA
Output Source Current, V
CC
= 3.3V
Output Source Current, V
CC
= 5V
Output Sink Current, V
CC
= 3.3V
Output Sink Current, V
CC
= 5V
q
q
q
q
V
BAT
= 1.2V, T
A
= 0°C to 70°C unless otherwise noted.
MIN
q
q
q
q
q
PARAMETER
V
CC
UVLO Trip Voltage (Note 4)
V
CC
UVLO Recovery Trip Voltage (Note 4)
V
BAT
UVLO Trip Voltage (Note 5)
Battery Charge Current
Programmable Trickle Charge Current Range
Fast Recharge Factor (Note 6)
Nominal Trickle Charge Multiplier Factor
Trickle Charge Clamp Voltage
CTL Input Threshold
CTL Input Low Time (Debounce Time)
CONDITIONS
LTC1558-3.3
LTC1558-5
LTC1558-3.3
LTC1558-5
TYP
3.00
4.55
3.10
4.70
0.9
16
1.6
10
0.5
MAX
3.10
4.70
3.20
4.85
0.95
21
2
1.85
12
0.55
250
UNITS
V
V
V
V
V
mA
mA
C/C
A/A
V
mV
ms
2.90
4.40
3.00
4.55
0.85
11
0.05
1.35
Backup Battery Charger
Fast Recharge
q
I
CHGT
= 1mA
I
CHGT
= 1mA
q
8
0.45
Pushbutton Reset
20
1.10
50
115
1.8
80
185
5
0.1
10
20
20
40
3.4
150
345
200
0.4
s
µs
ms
mV
V
mA
mA
mA
mA
Shutdown Pin (Note 3)
V
SHDN
I
SHDN
Feedback Pin
I
FB
1
10
nA
Logic Low, V
IL
Logic High, V
IH
V
CC
= 5V, V
SHDN
= 0V
q
q
q
0.8
2
8
15
V
V
µA
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2:
Quiescent current is measured during pushbutton reset.
Note 3:
Only applies to 16-pin version.
Note 4:
Thresholds will track each other and are guaranteed not to overlap.
Note 5:
Low cell voltage reset is only triggered when 0.25V < V
CTL
< 0.9V
for at least 20µs while in backup mode.
Note 6:
Fast recharge factor is defined as the ratio of charge replenished to
the NiCd battery during fast recharge to the charge drawn from the NiCd
battery during backup.
Note 7:
The LTC1558 switches automatically between the low and high
operating current levels. See Applications Information for more details.
3
LTC1558-3.3/LTC1558-5
TYPICAL PERFORMANCE CHARACTERISTICS
Output Power vs Battery Voltage
150
125
OUTPUT POWER (mW)
V
CC
= 5V (LTC1558-5)
V
BAK
= 6V
SWITCHING FREQUENCY (kHz)
100
75
50
25
0
1.0
1.1
1.2
1.3
NiCd TERMINAL VOLTAGE (V)
1.4
1558 G01
BACKUP TIME (HOURS)
Boost Converter Switching
Duty Cycle
100
TRICKLE CHARGE FACTOR (mA/mA)
10.5
CURRENT RATIO (mA/mA)
80
DUTY CYCLE (%)
60
40
20
V
BATT
= 1.2V
V
CC
= 3.3V (LTC1558-3.3)
I
PK
= 330mA
2
6
4
8
OUTPUT VOLTAGE, V
BAK
(V)
10
1558 G04
0
Fast Recharge Time (Assume
Fully Exhausted NiCd Battery)
60
50
RESET VOLTAGE (V)
40
30
20
10
0
6
TIME (HOURS)
4
3
2
1
0
4.7V
4.55V
0
1
2
3
4
SUPPLY VOLTAGE (V)
5
6
1558 G08
RESET VOLTAGE (V)
64
128
256
BATTERY CAPACITY (mAHr)
4
U W
512
1558 G07
Backup Time vs Battery Capacity
3.0
2.5
2.0
1.5
1.0
0.5
0
0
125
250
375
NiCd CELL CAPACITY (mAHr)
500
1558 G02
Boost Converter Switching
Frequency
125
V
BATT
= 1.2V
V
CC
= 3.3V (LTC1558-3.3)
I
PK
= 330mA
V
BATT
= 1.2V
V
BAK
= 6V
P
OUT
= 100mW
100
75
50
25
0
2
6
4
8
OUTPUT VOLTAGE, V
BAK
(V)
10
1558 G03
Trickle Charge Multiplier Factor
1.005
V
BATT
= 1.2V
10.0
9.5
9.0
8.5
8.0
7.5
0.05
Normalized Fast Recharge
Current vs Temperature
1.000
0.995
0.990
0.985
0.980
0.975
0.970
0.965
0.960
0.955
0.950
0.1
1
NiCd BATTERY TRICKLE CURRENT (mA)
2
0
25
50
TEMPERATURE (°C)
75
1558 G06
1558 G05
RESET Output Voltage
vs Supply Voltage
3.5
V
CC
= 5V (LTC1558-5)
5
3.0
2.5
2.0
1.5
1.0
0.5
0
RESET Output Voltage
vs Supply Voltage
V
CC
= 3.3V (LTC1558-3.3)
3.10V
3V
0
2
3
1
SUPPLY VOLTAGE (V)
4
1558 G09
LTC1558-3.3/LTC1558-5
PIN FUNCTIONS
Pin Numbers are Shown First for the SO-8 Package
Then the GN16 and S16 Packages
SW (Pins 1/1, 2):
Boost Converter Switching Node. Con-
nect a 22µH inductor from SW to the positive terminal of
the backup cell. In backup mode, this node is alternately
switched between ground and V
BAK
, generating the backup
output voltage. In fast or trickle charge mode, an internal
regulator outputs a constant DC current from this pin
through the 22µH inductor and into the NiCd battery.
During power-up or undervoltage lockout (UVLO), the SW
pin enters a high impedance state.
GND (Pins 2/4):
System Ground. The low power internal
circuitry returns to this pin in the 16-pin packages. GND
and PGND are bonded together to this pin in the SO-8.
CTL (Pins 3/5):
Control. This pin provides three functions.
In backup mode this pin enters a high impedance state and
monitors the backup battery cell voltage (V
BAT
). If V
BAT
drops below 0.9V, the LTC1558 enters into UVLO. During
trickle charge mode, an external resistor R
EXT
sets the
trickle charge current. In all modes, pulling the CTL pin
below 250mV will generate either a “soft” or “hard” reset
pulse. See the Applications Information section for more
information.
FB (Pins 4/7):
Output Voltage Feedback. This pin is fed to
the LTC1558’s internal comparators. The boost converter’s
output voltage is set with an external resistor divider
connected from V
BAK
to FB. The LTC1558 enters backup
mode when FB drops 7.5% below the internal reference
voltage (V
REF
). During backup, the boost converter runs
whenever FB drops below this (V
REF
– 7.5%) threshold.
The LTC1558 exits backup mode when FB rises above
(V
REF
– 6%).
RESET (Pins 5/11):
System Reset, Active Low. This is an
open-drain output. This pin provides a low going reset
signal to the system processor. A 200ms pulse is gener-
ated if the CTL pin is pulled low for more than two seconds
(“hard” reset) or when the LTC1558 comes out of UVLO.
The “hard reset” stops the internal boost converter if it is
running. This pin is held low whenever the LTC1558 is in
UVLO and is guaranteed to be valid when V
CC
is greater
than or equal to 1V.
RESET also provides a low going 100µs signal if the CTL
pin is pulled low for less than two seconds (“soft” reset).
Unlike hard reset, soft reset does not affect the LTC1558’s
current operating mode.
BACKUP (Pins 6/13):
Backup Active. This is an open-drain
output that pulls low unless the LTC1558 is in backup
mode. BACKUP signals the system controller that the
system is in backup mode so that it can reduce system
loading. BACKUP can also be used to drive the gate of a
P-channel MOSFET in series with the main system
regulator’s input. A 12V Zener diode is connected inter-
nally to this pin to act as a voltage clamp. See the
Applications Information section for more details.
V
CC
(Pins 7/14):
Power Supply Input. All internal circuits
except the boost converter are powered from this pin. A
0.1µF bypass capacitor is required from V
CC
to ground.
The UVLO detector inside the LTC1558 monitors V
CC
.If
V
CC
drops below the rated output voltage by greater than
9%, the LTC1558 enters UVLO mode and RESET is as-
serted. The LTC1558 will only exit from UVLO if V
CC
rises
to greater than – 6% of the rated output voltage. See the
Applications Information section for more details.
V
BAK
(Pins 8/15,16):
Backup Supply Output. The LTC1558’s
boost converter provides regulated output voltage to the
system through V
BAK
during backup mode.
16-Pin GN and SO Package
PGND (Pin 3):
Power Ground. The internal driver circuitry
returns to this pin. PGND should be connected to a low
impedance ground plane in close proximity to the NiCd
battery cell.
SHDN (Pin 6):
Chip Shutdown. A TTL-compatible active
low voltage at SHDN puts the LTC1558 into low power
shutdown mode. In shutdown, all internal circuits power
down and are held in a reset state. The SW, CTL and V
BAK
pins enter into high impedance states. In shutdown mode,
supply current drops to below 50µA and current drawn
from the backup cell drops to below 15µA.
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