LTC1559-3.3/LTC1559-5
Backup Battery Controller
with Fixed Output
DESCRIPTION
FEATURES
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Complete Battery Backup System in an SO-8,
16-Pin GN or SO Package
Generates Fixed Backup Voltage (3.07V/4.63V) 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
Onboard Power-Up and Push-Button Reset
Generator
Performs V
CC
Supervisory Functions
Reset Assertion Guaranteed at V
CC
= 1V
Short-Circuit Protection
Thermal Limiting
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.
APPLICATIONS
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Notebook Computers
Palmtop Computers/PDAs
Portable Instruments
Battery-Powered Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
*L1
22µH
**BACKUP
BATTERY
1.2V
NiCd
+
C1
1µF
R1
68k
1
8
BACKUP TIME (MINUTES)
S1
RESET
SW V
BAK
7
2
V
CC
GND
3
CTL
LTC1559-3.3
6
BACKUP
4
5
PS
RESET
+
C2
1µF
R2
100k
SYSTEM
µP
MAIN
BATTERY
4.5V TO 28V
Q1
+
C3
P-MOSFET
100µF
Si9424DY
V
OUT
10V
3.3V AT NORMAL MODE
* SUMIDA CD54-22µH
3A
V
BAK
** PANASONIC P-11AAH
33mA (3.07V) AT BACKUP MODE
† CONSULT LTC1435 DATA SHEET FOR
>33mA (3.3V) AT NORMAL MODE
1559 TA01
APPLICATION CIRCUIT INFORMATION
LTC1435
SYNCHRONOUS
BUCK
REGULATOR
†
U
U
U
Backup Time vs
V
BAK
Output Load Current
800
700
600
500
400
300
200
100
0
0
5
20
30
15
25
V
BAK
LOAD CURRENT (mA)
10
35
V
BAK
= 3.07V
NiCd CELL = P-11AAH
(110mA Hrs)
1559 TA02
1
LTC1559-3.3/LTC1559-5
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
Terminal Voltages
V
CC
........................................................................ 6V
V
BAK
.................................................................... 12V
SW ...................................................................... 14V
All Other Pins .............................. – 0.3V to V
CC
+ 0.3V
SW Input Currents ............................................. 500mA
PACKAGE/ORDER INFORMATION
ORDER PART
NUMBER
TOP VIEW
SW 1
GND 2
CTL 3
PS 4
8 V
BAK
7 V
CC
6 BACKUP
5 RESET
TOP VIEW
SW 1
SW 2
16 V
BAK
15 V
BAK
14 V
CC
13 BACKUP
12 RESET
11 RESET
10 NC
9
LOBAT
LTC1559CS8-3.3
LTC1559CS8-5
S8 PART MARKING
155933
15595
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
I
VCC
I
BAT
PARAMETER
Operating Voltage Range
Backup Battery Cell Voltage
Quiescent Supply Current (Note 2)
Peak Inductor Current (Backup)
Battery Backup Switching
V
BAT
= 1.2V, T
A
= 0°C to 70°C unless otherwise noted.
MIN
q
q
q
q
CONDITIONS
LTC1559-3.3
LTC1559-5
Boost Converter in Low Current Mode (Note 7)
Boost Converter in High Current Mode (Note 7)
V
CC
= 0V
LTC1559-3.3
LTC1559-5
LTC1559-3.3
LTC1559-5
LTC1559-3.3
LTC1559-5
LTC1559-3.3
LTC1559-5
I
BAT(SHDN)
Battery Standby Current
I
VCC(SHDN)
Supply Current During Shutdown (Note 3)
V
BAK(ON)
V
BAK(OFF)
V
LOBAT1
V
UVLO(ON)
V
CC
Backup Request/Booster Assertion
Trip Point (Note 4)
V
CC
Backup Deassertion Trip Point
(Note 4)
Low V
BAT
Detect (Note 3)
V
CC
UVLO Trip Voltage (Note 4)
V
UVLO(OFF)
V
CC
UVLO Trip Voltage (Note 4)
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
LTC1559CGN-3.3
LTC1559CGN-5
LTC1559CS-3.3
LTC1559CS-5
PGND 3
GND 4
CTL 5
SHDN 6
PS 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
3.5
5.5
UNITS
V
V
V
µA
mA
mA
µA
µA
V
V
V
V
V
V
V
V
V
2.900
4.400
1.0
80
225
1.2
155
165
330
0.1
3.011
4.475
3.061
4.550
0.95
2.904
4.400
3.061
4.550
3.070
4.625
3.119
4.700
1.00
3.003
4.550
3.119
4.700
1.5
250
225
445
15
50
3.127
4.775
3.176
4.850
1.05
3.102
4.700
3.176
4.850
q
q
q
q
q
q
q
q
q
q
q
q
q
LTC1559-3.3/LTC1559-5
ELECTRICAL CHARACTERISTICS
SYMBOL
V
LOBAT2
I
CHGF
I
CHGT
Q
RECH
Q
TRK
PARAMETER
V
BAT
UVLO Trip Voltage (Note 5)
Battery Charge Current During Fast Recharge
User-Programmable Trickle Charge
Current Range
Fast Recharge Factor (Note 6)
Nominal Trickle Charge Multiplier Factor
I
CHGT
= 1mA
I
CHGT
= 1mA
q
q
V
BAT
= 1.2V, T
A
= 0°C to 70°C unless otherwise noted.
MIN
q
CONDITIONS
TYP
0.9
16
MAX
0.95
21
2
UNITS
V
mA
mA
C/C
A/A
V
mV
ms
UVLO Reset Monitor
0.85
11
0.05
1.35
8
0.45
1.6
10
0.5
Backup Battery Charger
q
q
1.85
12
0.55
250
V
CTL(CLAMP)
CTL Clamp Voltage in Trickle Mode
Push-Button Reset
V
CTL
t
CTL
Reset Timer
t
HRESET
t
RST
V
RST1
V
RST
I
SC
Push-Button Duration for Hard Reset
RESET Pulse Width
RESET Output Voltage
RESET Output Voltage
RESET Output Current
Short-Circuit Current
PS Comparator
V
HYST
tr
V
SHDN
I
SHDN
Comparator Threshold Hysteresis
UVLO, Comparator Propagation Delay (Rising)
SHDN Input Threshold
SHDN Pin Bias Current
CTL Input Threshold
CTL Input Low Time (Debounce Time)
20
1.10
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
T
A
= 25°C
q
q
q
q
26
1.8
80
185
5
0.1
10
20
20
40
90
7.5
3.4
150
345
200
0.4
sec
µs
ms
mV
V
mA
mA
mA
mA
mV
µs
50
115
Internal V
CC
Monitor Comparator
Shutdown Pin (Note 3)
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 push-button reset.
Note 3:
Only applies to 16-pin version.
Note 4:
Although the V
BAK(ON)
, V
BAK(OFF)
, V
UVLO(ON)
and V
UVLO(OFF)
threshold voltages have a specification tolerance, they are guaranteed by
design and tested in production never 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 withdrawn from the
NiCd battery during backup.
Note 7:
The LTC1559 switches automatically between the low and high
operating current levels. See Applications Information for more details.
3
LTC1559-3.3/LTC1559-5
TYPICAL PERFORMANCE CHARACTERISTICS
Output Power vs Battery Voltage
140
120
OUTPUT POWER (mW)
I
PK
= 330mA
C
L
= 200µF
BACKUP TIME (HOURS)
SWITCHING FREQUENCY (kHz)
100
80
60
40
20
0
1.0
1.1
1.2
1.3
NiCd TERMINAL VOLTAGE (V)
1.4
1559 G01
Boost Converter Switching
Duty Cycle
100
10.5
TRICKLE CHARGE FACTOR (mA/mA)
CURRENT RATIO (mA/mA)
80
DUTY CYCLE (%)
60
40
LTC1559-3.3
V
BAT
= 1.2V
I
PK
= 330mA
2
6
4
8
OUTPUT VOLTAGE, V
BAK
(V)
10
1559 G04
20
0
Fast Recharge Time (Assume
NiCd Battery Fully Exhausted)
60
50
RESET VOLTAGE (V)
40
30
20
10
0
6
TIME (HOURS)
4
3
2
1
4.55V
4.7V
5
6
1559 G08
RESET VOLTAGE (V)
64
128
256
BATTERY CAPACITY (mA Hr)
4
U W
512
1559 G07
Backup Time vs Battery Capacity
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
50
125
250
375
NiCd CELL CAPACITY (mA Hr)
500
1559 G02
Boost Converter Switching
Frequency
125
LTC1559-3.3
V
BAT
= 1.2V
I
PK
= 330mA
V
BAT
= 1.2V
P
OUT
= 100mW
100
75
50
25
0
2
6
4
8
OUTPUT VOLTAGE, V
BAK
(V)
10
1559 G03
Trickle Charge Multiplier Factor
1.005
1.000
0.995
0.990
0.985
0.980
0.975
0.970
0.965
0.960
0.955
0.950
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
NiCd BATTERY TRICKLE CURRENT (mA)
1559 G05
Normalized Fast Recharge
Current vs Temperature
10.4
10.3
10.2
10.1
10.0
9.9
9.8
9.7
9.6
9.5
0
25
50
TEMPERATURE (°C)
75
1559 G06
RESET Output Voltage
vs Supply Voltage
4.0
LTC1559-5
5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
1
2
3
4
SUPPLY VOLTAGE (V)
RESET Output Voltage
vs Supply Voltage
LTC1559-3.3
3V
0
2
3
1
SUPPLY VOLTAGE (V)
3.12V
4
1559 G09
0
LTC1559-3.3/LTC1559-5
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 8-pin
package.
CTL (Pins 3/5):
Control. This pin provides three functions.
In backup mode this pin is a high impedance input and
monitors the backup battery cell voltage (V
BAT
). If V
BAT
drops below 0.9V, the LTC1559 enters UVLO. During
trickle charge mode, an external resistor R
EXT
sets the
trickle charge current. In all modes, pulling the CTL pin
below 250mV generates either a “soft” or “hard” reset
pulse. See the Applications Information section for more
information.
PS (Pins 4/7):
Power Supply Sense. This pin senses the
presence of the main supply and triggers the LTC1559 to
terminate backup mode. During backup, V
CC
is driven
externally by the LTC1559’s boost convert’s output (V
BAK
).
When PS > V
CC
during backup, the LTC1559 pulls down
the BACKUP pin, reconnecting the system regulator out-
put to the system V
CC
. The PS pin is needed in applications
that use a P-channel MOSFET (driven by the BACKUP
signal) to isolate the system regulator during backup. If
not needed, PS can be disabled by tying it to ground.
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 if the LTC1559 comes out of UVLO. This
“hard reset” stops the internal boost converter if it is
running. This pin is held low if the LTC1559 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 whenever
the CTL pin is pulled low for less than two seconds (“soft”
reset). Unlike hard reset, soft reset does not affect the
LTC1559’s current operating mode.
BACKUP (Pins 6/13):
System Backup Signal. This is a
TTL-compatible output driver that pulls low unless the
LTC1559 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 output. See the Applications Informa-
tion 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 LTC1559 monitors V
CC
. If
V
CC
drops below the rated output voltage by 9%, the
LTC1559 enters UVLO mode and RESET is asserted. The
LTC1559-3.3 exits UVLO if V
CC
rises to greater than
– 5.5% of the rated output voltage. The LTC1559-5 exits
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 LTC1559’s
boost converter provides the regulated output voltage to
the system through V
BAK
during backup mode.
16-Pin GN and SO Packages
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 LTC1559 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.
U
U
U
5
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