LTC1559CS8-3.3#PBF [Linear]
LTC1559 - Backup Battery Controller with Fixed Output; Package: SO; Pins: 8; Temperature Range: 0°C to 70°C;
| 型号： | LTC1559CS8-3.3#PBF |
| 厂家： | 
Linear |
| 描述： | LTC1559 - Backup Battery Controller with Fixed Output; Package: SO; Pins: 8; Temperature Range: 0°C to 70°C 电池 控制器 |
| 文件： | 总20页 (文件大小：347K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC1559-3.3/LTC1559-5
Backup Battery Controller
with Fixed Output
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FEATURES
DESCRIPTION
The LTC®1559 is a backup battery controller that provides
all the functions necessary to implement a backup 3.3V or
5VpowersupplyusingasingleNiCdcell.Itincludesa1.2V
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.
■
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
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.
■
Onboard Power-Up and Push-Button Reset
Generator
■
Performs VCC Supervisory Functions
■
Reset Assertion Guaranteed at VCC = 1V
Short-Circuit Protection
Thermal Limiting
■
■
The LTC1559’s automatic backup switching scheme
requires minimum intervention from the host system and
provides feedback to the host to minimize system loading
inthebackupstate. ItsinternalVCC faultdetectorandreset
generator eliminate the need for a separate microproces-
sor supervisory chip in most applications.
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APPLICATIONS
■
Notebook Computers
Palmtop Computers/PDAs
Portable Instruments
Battery-Powered Systems
■
■
■
The LTC1559 is available in an SO-8, 16-pin GN or SO
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
Backup Time vs
VBAK Output Load Current
*L1
22µH
800
**BACKUP
+
1
8
C1
V
BAK
= 3.07V
BATTERY
1.2V
R1
68k
V
700
600
500
400
300
200
100
0
SW
GND
+
1µF
NiCd CELL = P-11AAH
(110mA Hrs)
BAK
V
7
2
3
C2
1µF
NiCd
CC
R2
CTL
100k
LTC1559-3.3
S1
RESET
6
5
SYSTEM
BACKUP
4
µP
PS
RESET
†
LTC1435
MAIN
BATTERY
4.5V TO 28V
SYNCHRONOUS
BUCK
REGULATOR
Q1
P-MOSFET
Si9424DY
+
C3
100µF
10V
V
OUT
3.3V AT NORMAL MODE
3A
* SUMIDA CD54-22µH
** PANASONIC P-11AAH
† CONSULT LTC1435 DATA SHEET FOR
APPLICATION CIRCUIT INFORMATION
V
BAK
20
LOAD CURRENT (mA)
30
35
0
5
10
15
25
33mA (3.07V) AT BACKUP MODE
>33mA (3.3V) AT NORMAL MODE
V
BAK
1559 TA01
1559 TA02
1
LTC1559-3.3/LTC1559-5
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ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
BAK Output Current................... Short-Circuit Protected
Terminal Voltages
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
VCC ........................................................................ 6V
VBAK .................................................................... 12V
SW ...................................................................... 14V
All Other Pins .............................. –0.3V to VCC + 0.3V
SW Input Currents ............................................. 500mA
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PACKAGE/ORDER INFORMATION
TOP VIEW
ORDER PART
ORDER PART
SW
SW
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
V
V
V
NUMBER
NUMBER
BAK
BAK
CC
TOP VIEW
LTC1559CS8-3.3
LTC1559CS8-5
LTC1559CGN-3.3
LTC1559CGN-5
LTC1559CS-3.3
LTC1559CS-5
PGND
GND
CTL
1
2
3
4
8
7
6
5
SW
GND
CTL
PS
V
V
BAK
BACKUP
RESET
RESET
NC
CC
BACKUP
RESET
SHDN
PS
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
NC
LOBAT
155933
15595
TJMAX = 125°C, θJA = 130°C/ W
GN PACKAGE
S PACKAGE
16-LEAD PLASTIC SSOP 16-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 110°C/ W (GN)
T
JMAX = 125°C, θJA = 110°C/ W (S)
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS VBAT = 1.2V, TA = 0°C to 70°C unless otherwise noted.
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Battery Backup Switching
V
V
Operating Voltage Range
LTC1559-3.3
LTC1559-5
●
●
2.900
4.400
3.5
5.5
V
V
CC
Backup Battery Cell Voltage
●
●
1.0
1.2
1.5
V
BAT
VCC
BAT
I
I
Quiescent Supply Current (Note 2)
Peak Inductor Current (Backup)
155
250
µA
Boost Converter in Low Current Mode (Note 7)
Boost Converter in High Current Mode (Note 7)
●
●
80
225
165
330
225
445
mA
mA
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I
Battery Standby Current
V
= 0V
CC
●
●
0.1
15
50
µA
µA
BAT(SHDN)
VCC(SHDN)
Supply Current During Shutdown (Note 3)
V
V
Backup Request/Booster Assertion
CC
LTC1559-3.3
LTC1559-5
●
●
3.011 3.070 3.127
4.475 4.625 4.775
V
V
BAK(ON)
Trip Point (Note 4)
V
V
Backup Deassertion Trip Point
LTC1559-3.3
LTC1559-5
●
●
3.061 3.119 3.176
4.550 4.700 4.850
V
V
BAK(OFF)
CC
(Note 4)
V
V
Low V
Detect (Note 3)
BAT
●
0.95
1.00
1.05
V
LOBAT1
V
V
UVLO Trip Voltage (Note 4)
LTC1559-3.3
LTC1559-5
●
●
2.904 3.003 3.102
4.400 4.550 4.700
V
V
UVLO(ON)
CC
CC
V
UVLO Trip Voltage (Note 4)
LTC1559-3.3
LTC1559-5
●
●
3.061 3.119 3.176
4.550 4.700 4.850
V
V
UVLO(OFF)
2
LTC1559-3.3/LTC1559-5
ELECTRICAL CHARACTERISTICS VBAT = 1.2V, TA = 0°C to 70°C unless otherwise noted.
SYMBOL PARAMETER
UVLO Reset Monitor
CONDITIONS
MIN
TYP
0.9
16
MAX
UNITS
V
V
UVLO Trip Voltage (Note 5)
●
0.85
0.95
V
LOBAT2
BAT
Backup Battery Charger
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Battery Charge Current During Fast Recharge
●
●
11
21
2
mA
mA
CHGF
CHGT
User-Programmable Trickle Charge
Current Range
0.05
Q
Q
Fast Recharge Factor (Note 6)
1.35
8
1.6
10
1.85
12
C/C
A/A
V
RECH
Nominal Trickle Charge Multiplier Factor
CTL Clamp Voltage in Trickle Mode
I
I
= 1mA
= 1mA
●
●
TRK
CHGT
CHGT
V
0.45
0.5
0.55
CTL(CLAMP)
Push-Button Reset
V
CTL Input Threshold
250
mV
ms
CTL
CTL
t
CTL Input Low Time (Debounce Time)
20
26
Reset Timer
t
t
Push-Button Duration for Hard Reset
RESET Pulse Width
1.10
1.8
3.4
sec
HRESET
RST
V
CTL
V
CTL
Low for <t
Low for >t
(Soft Reset)
(Hard Reset)
●
●
50
115
80
185
150
345
µs
ms
HRESET
HRESET
V
V
RESET Output Voltage
RESET Output Voltage
RESET Output Current
V
V
= 1V, I = 10µA
SINK
●
●
5
200
0.4
mV
V
RST1
RST
CC
CC
= 4.25V, I
= 1.6mA
0.1
SINK
I
Output Source Current V = 3.3V
Output Source Current V = 5V
10
20
mA
mA
SC
CC
CC
Short-Circuit Current
Output Sink Current V = 3.3V
20
40
mA
mA
CC
Output Sink Current V = 5V
CC
PS Comparator
Comparator Threshold Hysteresis
Internal V Monitor Comparator
V
T = 25°C
A
90
mV
HYST
CC
tr
UVLO, Comparator Propagation Delay (Rising)
7.5
µs
Shutdown Pin (Note 3)
V
SHDN Input Threshold
Logic Low, V
●
●
0.8
15
V
V
SHDN
IL
IH
Logic High, V
2
I
SHDN Pin Bias Current
V
CC
= 5V, V
= 0V
●
8
µA
SHDN
SHDN
The
●
denotes specifications which apply over the full operating
Note 5: Low cell voltage reset is only triggered when 0.25V < V < 0.9V
for at least 20µs while in backup mode.
CTL
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 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.
Note 4: Although the V
, V
, V
and V
BAK(ON) BAK(OFF) UVLO(ON) UVLO(OFF)
threshold voltages have a specification tolerance, they are guaranteed by
design and tested in production never to overlap.
3
LTC1559-3.3/LTC1559-5
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TYPICAL PERFORMANCE CHARACTERISTICS
Boost Converter Switching
Frequency
Output Power vs Battery Voltage
Backup Time vs Battery Capacity
140
120
100
80
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
125
100
75
50
25
0
I
= 330mA
= 200µF
V
BAT
P
OUT
= 1.2V
= 100mW
LTC1559-3.3
PK
L
C
V
PK
= 1.2V
BAT
I
= 330mA
60
40
20
0
4
6
8
2
1.0
1.1
1.2
1.3
1.4
50
125
250
375
500
10
NiCd TERMINAL VOLTAGE (V)
NiCd CELL CAPACITY (mA Hr)
OUTPUT VOLTAGE, V
(V)
BAK
1559 G03
1559 G01
1559 G02
Boost Converter Switching
Duty Cycle
Normalized Fast Recharge
Current vs Temperature
Trickle Charge Multiplier Factor
1.005
1.000
0.995
0.990
0.985
0.980
0.975
100
80
60
40
20
0
10.5
10.4
10.3
10.2
10.1
10.0
9.9
0.970
0.965
9.8
LTC1559-3.3
9.7
0.960
0.955
0.950
V
I
= 1.2V
BAT
PK
= 330mA
9.6
9.5
75
4
6
8
0.8
1.0
0
25
50
2
10
0
0.2 0.4 0.6
1.2 1.4 1.6 1.8 2.0
TEMPERATURE (°C)
OUTPUT VOLTAGE, V
(V)
NiCd BATTERY TRICKLE CURRENT (mA)
BAK
1559 G06
1559 G04
1559 G05
RESET Output Voltage
vs Supply Voltage
Fast Recharge Time (Assume
NiCd Battery Fully Exhausted)
RESET Output Voltage
vs Supply Voltage
60
50
40
30
20
10
0
6
5
4
3
2
1
0
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
LTC1559-5
LTC1559-3.3
4.55V
4.7V
3.12V
3V
64
128
256
512
0
2
3
4
5
6
0
2
3
4
1
1
BATTERY CAPACITY (mA Hr)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
1559 G07
1559 G08
1559 G09
4
LTC1559-3.3/LTC1559-5
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PIN FUNCTIONS
Pin Numbers Are Shown First for the SO-8 Package
Then the GN16 and S16 Packages
is guaranteed to be valid when VCC is greater than or equal
to 1V.
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
switchedbetweengroundandVBAK,generatingthebackup
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.
Duringpower-uporundervoltagelockout(UVLO), theSW
pin enters a high impedance state.
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.
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.
V
CC (Pins 7/14): Power Supply Input. All internal circuits
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 (VBAT). If VBAT
drops below 0.9V, the LTC1559 enters UVLO. During
trickle charge mode, an external resistor REXT 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.
except the boost converter are powered from this pin. A
0.1µF bypass capacitor is required from VCC to ground.
The UVLO detector inside the LTC1559 monitors VCC. If
VCC drops below the rated output voltage by 9%, the
LTC1559 enters UVLO mode and RESET is asserted. The
LTC1559-3.3 exits UVLO if VCC rises to greater than
–5.5% of the rated output voltage. The LTC1559-5 exits
UVLO if VCC rises to greater than –6% of the rated output
voltage.SeetheApplicationsInformationsectionformore
details.
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, VCC is driven
externallybytheLTC1559’sboostconvert’soutput(VBAK).
When PS > VCC during backup, the LTC1559 pulls down
the BACKUP pin, reconnecting the system regulator out-
puttothesystemVCC. ThePSpinisneededinapplications
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.
VBAK(Pins8/15,16):BackupSupplyOutput.TheLTC1559’s
boost converter provides the regulated output voltage to
the system through VBAK 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 VBAK
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.
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
5
LTC1559-3.3/LTC1559-5
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PIN FUNCTIONS
RESET (Pin 12): System Reset, Active High. This is a TTL-
compatible output driver. It can connect to systems that
require active high logic. The RESET output will go high if
RESET is pulled low.
LOBAT (Pin 9): Low Backup Battery Detector Output. This
is an open-drain output with an internal weak pull-up. It is
asserted if the NiCd cell terminal voltage drops below
1.0V. This pin is pulled high if the LTC1559 is in trickle
charge mode.
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BLOCK DIAGRAM
P1
SW
V
BAK
V
/V
CC BAK
CHARGER
N1
CTL
BOOST/BACKUP
LOGIC
PS
+
–
BACKUP
RESET
RESET
LEVEL SENSE
AND DEBOUNCE
RESET
GENERATOR
V
REF
V
CC
V
REF
GAS GAUGE
+
–
–
+
LOBAT
UVLO
DETECTOR
THERMAL
LIMIT
BANDGAP
= 1.272V
SHUTDOWN
LOGIC
SHDN
V
REF
1559 BD
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SWITCHING WAVEFORMS
Cold Power Boot-Up (Main Battery Replaced/Turned On)
Simplified LTC1559 Connections in a Battery Backup System
RATED BATTERY TERMINAL VOLTAGE
TO
SYSTEM
CONTROL
22µH
1
RESET
LTC1559
SW
1.2V
NiCd
RATED V VOLTAGE
CC
PS
V
CC
V
BAT
4
2
BACKUP
V
BAK
–5.5% (LTC1559-3.3)
3
–6% (LTC1559-5)
BACKUP
SYSTEM
PS
V
IN
V
OUT
V
CC
200ms
V
Q
CC
V
EXT
BAT
MAIN
MAIN SYSTEM
REGULATOR
C
OUT
BATTERY
RESET
1559 SW01
FOR MORE DETAILED CIRCUIT APPLICATION SCHEMATICS,
PLEASE REFER TO THE TYPICAL APPLICATIONS SECTION
BACKUP
1559 SW02
6
LTC1559-3.3/LTC1559-5
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SWITCHING WAVEFORMS
Cold Power Boot-Up Description
3. The LTC1559’s internal bandgap wakes up. QEXT turns
on and VCC = PS. The LTC1559’s internal boost con-
verter does not turn on as RESET remains asserted.
1. System regulator starts to ramp up the output (PS)
once the VBAT voltage increases beyond the minimum
input value.
4. RESETisassertedforafurther200msafterVCC reaches
–5.5% of its rated VCC value for the LTC1559-3.3 and
–6% of its rated VCC value for the LTC1559-5.
2. VCC startstoincreaseoncePSishighenoughtoturnon
QEXT’s body diode. RESET is asserted when VCC is less
than or equal to 1V.
Backup Mode (Main Battery Discharged)—
LTC1559-3.3
1V
1.2V
0.9V
V
NiCd
BOOST CONVERTER OUTPUT
–7%
–5.5%
–7%
–7%
V
CC
t
t
f
r
BACKUP
INDUCTOR
CURRENT
t
r
t
r
“1”
RESET
t
r
“1”
LOBAT
(1)
(2)
(3)
(4)
1559 SW03
Backup Mode Description
3. Recovery from Backup Mode. While the boost con-
verter is running, the main battery is restored. This
causes the system regulator to increase PS above VCC.
When PS > VCC or VCC > VCC(rated value) –5.5%, the
BACKUPpindeassertsandtheboostconverterfinishes
its last cycle.
1. Trigger into Backup Mode. Main battery fails and VCC
drops 7% below the rated value. The backup pin is
asserted after a tr delay time and the boost converter is
turned on.
2. Backup Mode. The LTC1559’s boost converter charges
and discharges the inductor with 165mA peak current.
If VCC doesn’t increase above VCC(rated value) – 7%
(due to a heavy load), the boost converter increases
peak charging current to 330mA. If VCC rises above
VCC(rated value) – 7%, the boost converter stops and
the backup pin remains asserted.
4. Trigger into UVLO. During backup, the 1.2V NiCd cell is
dischargedanditsterminalvoltagefalls.TheLOBATpin
is asserted to give an early warning if the cell voltage
drops below 1V. RESET is asserted when the cell
voltage drops below 0.9V and the LTC1559 enters
UVLO mode.
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LTC1559-3.3/LTC1559-5
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APPLICATIONS INFORMATION
Table 1. LTC1559-3.3 Operating Modes
OPERATING MODES
Overview
CONDITIONS
TheLTC1559isaversatilebackupbatterycontrolsystem
designed to provide all the functions necessary to imple-
mentacomplete, highlyintegratedbackupsystemwithin
a single chip. It allows the system to maintain its rated
supply voltage during backup, offering maximum sys-
tem design flexibility. The LTC1559 allows the use of a
low cost rechargeable NiCd cell for backup, eliminating
the need for expensive, replaceable 4.5V lithium backup
cells.
UVLO Reset
1V < V < V (rated value) – 9% or
CC CC
V
< 0.9V
BAT
Push-Button Reset
UVLO Reset Recovery
Backup Mode Activation
Backup Mode Exit
V
< 250mV
CTL
V
> V (rated value) – 5.5%
CC
CC
CC
V
< V (rated value) – 7%
CC
CC
V
> V (rated value) – 5.5%
CC
or PS > V
CC
Boost Converter Activation
Boost Converter Deactivation
V
< V (rated value) – 7%
CC
CC
CC
V
> V (rated value) – 7%
CC
The LTC1559 includes an onboard boost converter
designed to generate a fixed voltage (3.07V for 3.3V parts
and 4.625V for 5V parts) from a single 1.2V NiCd cell.
When connected to the system DC/DC converter’s output,
the LTC1559 enables the system connected to the VCC rail
to continue operation when the main power supply fails. A
“smart” recharging circuit uses an accumulating gas
gauge to measure the charge extracted from the backup
battery during a backup cycle. This measured charge is
then replaced in a fast recharge cycle, without wasting
excess power or overcharging the backup cell. An exter-
nally adjustable trickle charge circuit maintains the cell
chargeafterthefastchargecyclehascompleted, minimiz-
ing drain from the main battery during standby.
Table 2. LTC1559-5 Operating Modes
OPERATING MODES
CONDITIONS
UVLO Reset
1V < V < V (rated value) – 9%
CC CC
or V
< 0.9V
BAT
Push-Button Reset
UVLO Reset Recovery
Backup Mode Activation
Backup Mode Exit
V
< 250mV
CTL
V
> V (rated value) – 6%
CC
CC
V
< V (rated value) – 7.5%
CC
CC
V
> V (rated value) – 6%
CC
CC
or PS > V
CC
Boost Converter Activation
Boost Converter Deactivation
V
< V (rated value) – 7.5%
CC
CC
CC
V
> V (rated value) – 7.5%
CC
Boost Converter Operation
Included in the LTC1559 is a complete backup circuit that
monitors the main system power and automatically
switchesinthebackupcircuitastheprimarypowersupply
falls away (due to a weak or disconnected main battery).
The LTC1559 also performs VCC supervisory functions
during normal system operations. An LTC1559-3.3
monitors a 3.3V supply voltage at its VCC pin while an
LTC1559-5 monitors a 5V supply at its VCC pin. In both
cases, the LTC1559 derives power for the majority of the
internal circuitry (except for the boost converter) from its
VCC pin. Table 1 shows the signal conditions for the
various operating modes of the LTC1559-3.3. Table 2
shows the signal conditions for the various operating
modes of the LTC1559-5.
The LTC1559 uses an onboard boost converter with a
fixed peak current architecture that provides a simple and
flexible system solution while eliminating the need for
conventional frequency compensation. The boost
converter’s output, set to 93% (LTC1559-3.3) or 92.5%
(LTC1559-5) of the rated VCC, supports the system VCC
during backup. It supplies a minimum backup power of
100mW. The boost converter operates in a modified
pulse-skippingmode;eachswitchcycletransfersaknown
amount of charge from the backup cell to the regulated
output.Thispreventsuncontrolleddischargeofthebackup
cell and allows the LTC1559 to accurately measure the
charge removed from the backup cell by counting the
charge pulses.
The LTC1559 enters backup mode when the main battery
voltage drops and causes VCC, the system regulator’s
output, to fall. As shown in Figure 1, VCC is scaled down
by an internal resistor divider and fed to the LTC1559’s
backup comparators. These compare the scaled voltage
8
LTC1559-3.3/LTC1559-5
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SYSTEM
V
CC
V
CC
LTC1559
+
C
OUT
SYSTEM
REGULATOR
V
BAK
BOOST
CONVERTER
R1
R2
BACKUP
LOGIC
BACKUP
V
REF
PS
1559 F01
Figure 1. Typical LTC1559 Connection
with an internal trimmed VREF (1.272V), switching the
LTC1559 into backup mode if VCC drops 7%
(LTC1559-3.3) or 7.5% (LTC1559-5) below its rated
value. Upon entering backup mode, the BACKUP pin is
asserted and the internal boost converter turns on. The
BACKUP signal turns off the external P-channel MOSFET
(ifused),isolatingthesystemregulatorfromtheLTC1559.
The boost converter charges the VCC capacitor, COUT, of
the system regulator until VCC rises above VCC (rated
value) – 7% (LTC1559-3.3) or VCC (rated value) – 7.5%
(LTC1559-5).
ferred for the first two consecutive switch cycles. If VCC
falls below VCC (rated value) –7% (LTC1559-3.3), the
boost operation starts by connecting the SW pin internally
to ground through an internal 0.5Ω N-channel MOSFET
(N1 in the Block Diagram). The current through the exter-
nal 22µH inductor rises linearly through this switch.
When the switch current reaches an internally preset level
of 165mA, the boost converter connects the SW pin to the
VBAK pin through an internal 2Ω P-channel MOSFET. The
inductor current discharges through the P-channel (P1 in
the Block Diagram) and charges up the system’s VCC
capacitor (COUT of the system regulator, Figure 1). The
inductor current falls at a rate proportional to the differ-
ence between the backup cell voltage and the output
voltage VBAK. When the inductor current reaches zero,
indicating all of its energy has been transferred to the
output capacitor, the LTC1559 monitors the VCC voltage.
If VCC has increased above the VCC (rated value) –7%
(LTC1559-3.3) threshold, the boost converter shuts off
both switches and waits for VCC to drop below VCC (rated
value) –7% (LTC1559-3.3) again.
Once VCC rises above VCC (rated value) – 7% (LTC1559-
3.3), the boost converter deactivates and the freshly
chargedVCC capacitorCOUT suppliespowertothesystem.
The cycle repeats again when the VCC capacitor’s charge
is drained away and VCC again drops below VCC (rated
value) – 7% (LTC1559-3.3). The BACKUP pin remains
asserted until the main battery is restored. This ensures
that the LTC1559 does not switch in and out of backup
mode unnecessarily.
The LTC1559’s boost converter minimizes output ripple
under light load conditions by reducing the charge trans-
1
BOOST
CYCLE
330mA
(PEAK)
V
BAK
ESR RIPPLE
165mA
(PEAK)
1559 F03
DISCHARGE
PERIOD
CHARGE
PERIOD
CH
1559 F02
LIGHT CURRENT MODE
HEAVY CURRENT MODE
t
t
DISCH
Figure 2. Inductor Current During Switching
Figure 3. VBAK Ripple
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If VCC is still less than VCC (rated value) –7% (LTC1559-
3.3) after the first boost cycle, the LTC1559 immediately
reconnects SW to ground, repeating the boost cycle. If
after two consecutive pulses, VCC is still not above the
Assuming ESR = 0.2Ω, IIND(PEAK) = 330mA, VCC = 5V,
VRIPPLE(P-P) = (IIND(PEAK))(RESR(CAP)
= (330mA)(0.2Ω)
)
boost threshold VCC (rated value) –7% (LTC1559-3.3)
,
= 66mV
the LTC1559 decides that the load is not so light after all,
and doubles the internal inductor charging current limit to
330mA for subsequent cycles. This is high current mode.
By doubling the peak inductor current, each boost cycle
effectively carries four times more energy compared to
low current mode (E = 1/2 • LI2), doubling the available
output power. When VCC exceeds the VCC (rated value)
–7% (LTC1559-3.3) boost threshold, the LTC1559 stops
theboostconverterandresetstheinternal2-pulsecounter.
The next time VCC falls below VCC (rated value) –7%
(LTC1559-3.3),theboostconverterrestartsinlowcurrent
mode for at least two boost cycles. Moderate or changing
loads cause the LTC1559 to shift between the two peak
inductor current limits, keeping the output in tight regula-
tion. Near its maximum load capability, the LTC1559 will
stay in 330mA high current mode and the output voltage
VBAK will hover around VCC (rated value) – 7%
Since VCC must be scaled down internally, the external
resistor ratio:
= 5V/1.272V
= 3.931
Therefore the ripple seen by the VCC comparators is:
= 66mV/3.931
= 16.79mV
The discharge time period,
tDISCH = (L • IIND(PEAK))/(VBAK – VBAT
)
= (22µH • 330mA)/(4.625 – 1.2V)
= 2.12µs
For VCC = 3.3V and IIND(PEAK) = 330mA,
VRIPPLE(P-P) = 66mV
(LTC1559-3.3)
.
RB resistor ratio = 3.3/1.272 = 2.594
Ripple voltage = 25.4mV
tDISCH = 3.9µs
VCC Capacitor ESR
The type of output capacitor and the rated VCC value will
affect the LTC1559’s output ripple and efficiency. In most
applications, the VCC capacitor is primarily determined by
the requirements of the main power supply. Such a
capacitor will generally meet the requirements of the
LTC1559. In unusual circumstances or circuits where
the main system VCC capacitor is located some distance
away from the LTC1559, a local output capacitor may be
necessary.
The internal VCC comparators are designed to have a slow
response time to filter away this ripple. The VCC (rated
value) – 5.5% (LTC1559-3.3) and VCC(rated value) – 9%
comparators have a 6µs rising edge delay and 2µs falling
edge delay. The VCC (rated value) – 7% (LTC1559-3.3)
comparator has a similar 6µs rising time delay but a much
longer falling time delay of 20µs. This enables the com-
paratortocontroltheboostconverterproperly,andavoids
turning off the boost converter prematurely due to false
triggering by the ESR ripple.
The ripple on the VCC pin is equal to the capacitor ESR
voltage drop due to the boost converter’s output current
pulses. The ripple frequency and output duty cycle is
proportional to the inductor discharge time. Given a fixed
inductor value (22µH) and a known peak current limit, the
booster’s discharge time in each boost cycle is propor-
tionaltothedifferencebetweenVBAK (93%oftheratedVCC
for the LTC1559-3.3 and 92.5% of the rated VCC for the
LTC1559-5) and the battery cell voltage, VBAT (1.2V).
Exit from Backup
When a main battery is inserted into the system, the
LTC1559 follows a specific sequence to exit backup mode
and return control to the main supply. The sequence
depends on the type of main power supply used. In
systems where the main supply’s output impedance is
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LTC1559-3.3/LTC1559-5
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high when inactive (typically a boost regulator with an
output catch diode), the LTC1559 detects the return of the
main supply by watching for VCC to exceed VCC (rated
value) – 5.5% (LTC1559-3.3). The LTC1559 then shuts
down its internal boost converter and begins to recharge
the NiCd cell. In such applications, the PS pin is not used
and can be tied to ground. No external P-channel MOSFET
is required to isolate the main supply from the system VCC
during backup.
to the load while charge on the VCC capacitor drains away.
If VCC drops below VCC (rated voltage) –9% for more than
7.5µs, the LTC1559’s VCC supervisory circuit activates
UVLO mode, shutting off the boost converter and assert-
ing the Reset pins. The 7.5µs delay prevents the LTC1559
from being fooled by brief transients or noise spikes on its
V
CC pin. Upon receipt of the reset signal, the host system
should shut down in an orderly manner. The LTC1559’s
V
CC supervisory circuit will remain alive until VCC is less
than 1V to ensure a valid RESET pin signal.
In systems where the main supply’s output impedance is
low when inactive (typically buck regulators), the main
supply must be disconnected from the system VCC during
backup to prevent the inactive supply from loading the
LTC1559. This is typically accomplished using an external
P-channel MOSFET as shown in Figure 1. When the main
supply is restored, the P-channel MOSFET’s body diode
forward-biases. This allows current to flow into the sys-
tem VCC, but the forward drop across this diode may
prevent VCC from reaching the VCC (rated value)
– 5.5% (LTC1559-3.3) threshold that deactivates the
LTC1559’s backup mode. In such systems, the PS pin
should connect directly to the output of the main system
supply. When the system regulator’s voltage rises about
2.5% above the backup VCC, the PS comparator triggers
and causes the LTC1559 to deassert the BACKUP pin
signal. This signals the system controller to restore sys-
tem loading and resume normal operation. At the same
time, the external P-MOSFET is driven by the BACKUP
signal. The P-channel MOSFET turns on and allows the
main regulator to bypass its body diode and drive the
system VCC directly.
Backup Cell Voltage Monitoring
As the boost converter removes charge from the backup
NiCd cell, the cell’s terminal voltage falls. Permanent
damage to the NiCd cell can occur if it is discharged to
below 0.9V. To prevent this, the LTC1559 monitors the
cell’s terminal voltage through the CTL pin during backup.
If the CTL pin drops below 0.9V for more than 20µs, the
UVLO circuit shuts down the boost converter and asserts
the RESET and RESET pins. Since the CTL pin can also be
connected to an external push-button reset, the LTC1559
includes internal logic to ensure that the low cell voltage
reset is triggered only if the CTL pin is between 0.9V and
0.25V. This will prevent a push-button reset (which pulls
CTL below 250mV) from being mistaken as a low cell
voltage condition. Unusual situations where the NiCd cell
voltage drops drastically below 0.25V will also trigger
UVLO, since the LTC1559 will treat this as a “hard” reset
after two seconds.
AnoptionalLOBAToutput,availableinthe16-pinGNorSO
package, can be used to signal the system if the cell
voltage falls below 1V, giving an early warning that the
backup cell is heavily discharged. The LOBAT pin is
disabled if the LTC1559 is in trickle charge mode,
because the CTL pin is regulated to 0.5V by the LTC1559.
Sincetheusercanreplacethemainbatteryanytimeduring
the LTC1559’s backup operation, the BACKUP signal may
be deasserted while the boost converter is switching. To
prevent the potential problem of residual energy in the
inductor, the LTC1559 will only stop the boost converter
after it completes the current boost converter cycle.
Fault Protection and Thermal Limit
The LTC1559’s boost converter incorporates two internal
timers that turn off the switch transistors if the inductor
charge or discharge time gets abnormally long.
UVLO Under Excessive Backup Load
Very heavy loads (above the LTC1559’s maximum power
output) will pull the boost converter’s output below the
boost threshold. Under these conditions, the LTC1559’s
boostconvertercontinuestosupply330mAcurrentpulses
The inductor charge time may get abnormally long if the
NiCdcellvoltagedropsbelow0.25Vwithouttriggeringthe
0.25V < VBAT < 0.9V low cell voltage comparator. In this
11
LTC1559-3.3/LTC1559-5
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case, the NiCd cell is assumed to be damaged and the
LTC1559’s priority is shutting down the system grace-
fully. In this case, the timer will shut off the N-channel
switch transistor after a maximum charging time (14µs).
The boost converter continues switching but delivers
reduced output power, causing VCC to drop. The LTC1559
enters UVLO if VCC drops below VCC(rated value)
– 9% or if the LTC1559 detects that CTL is lower than
0.25V for two seconds, in which case “hard” reset occurs.
after approximately 2.2 hours, equivalent to about
512mAhr of charge.
Upon entering recharge mode (after the main battery is
restored) the LTC1559 connects a 16mA fast recharge
current source from VCC to the SW pin. At the same time,
an internal free running oscillator counts down the gas
gaugecounterataratedesignedtotypicallyreplace160%
of the charge previously removed from the backup cell.
When the gas gauge counter reaches zero, the LTC1559
reduces the charging current at the SW pin to the user-
programmed trickle charge current level.
The discharge time can also get abnormally long if a
serious overload condition occurs during switching. The
timer shuts off the P-channel pass transistor after 10µs,
protectingtheboostconverter. TheLTC1559entersUVLO
as VCC drops below VCC(rated value) – 9%.
Under some circumstances, the LTC1559 can exit backup
mode with invalid gas gauge contents. This occurs under
three possible conditions:
In addition, the LTC1559 has safe area operation protec-
tionwithaninternalthermalshutdowncircuit.Ifthedevice
is overloaded for a long period of time, the thermal
shutdown circuit forces the LTC1559 into UVLO. The
threshold temperature for thermal shutdown is typically
155°C.
1. The backup cell was completely exhausted during a
backup cycle and the LTC1559 entered UVLO.
2. Thebackupcellwasreplacedwhilethemainsupplywas
disabled.
3. A backup cycle was terminated prematurely by a “hard”
reset or an output overload.
The LTC1559’s boost converter is designed so that no
current drains from the battery to the load during output
short circuit or VCC = 0V conditions. This assures that the
system can be powered down for a long period of time.
Thiseliminatestheriskoffindinganonfunctioningbackup
system upon power-up.
Inthesecases,theLTC1559assumesthatthebackupcell
is exhausted and presets the gas gauge counter to a
default capacity of 128mAhr. It then initiates a recharge
cycle.
Setting the gas gauge to this default value results in a fast
recharge cycle long enough to replenish 1.6 times
128mAhr into the backup cell (13.9 hours). If the backup
cell is actually exhausted, it will be fully recharged. If the
battery is partially or fully charged, or is significantly
smaller than 128mAhr capacity, the extra charging time is
wasted. However, the LTC1559’s 16mA fast charge cur-
rent is not high enough to damage the cell. Once the full-
count recharge has been completed, the backup cell is
assumed to be fully charged and subsequent backup/
recharge cycles resume normally.
Backup Cell Fast Recharge
The LTC1559 includes an onboard gas gauge circuit,
consisting of a 23-bit divider and a 9-bit up/down counter.
The gas gauge logic assumes that the boost converter
uses a 22µH inductor, allowing it to accurately measure
battery charge by counting pulses. The gas gauge counts
up from zero as charge is removed from the backup cell in
backup mode. It takes 8.4 million 165mA boost pulses
(low current mode) to increment the up/down counter by
one count. In high current mode, the 330mA pulses skip
the first two bits of the divider because each 330mA pulse
carries four times as much energy as a 165mA pulse. At
maximum load and VCC = 4.625V (LTC1559-5), the gas
gauge counter will increment by one count every 7.5µs
while the boost converter is running. Full count is reached
Although the LTC1559 will not fully recharge backup cells
larger than 128mAhr capacity upon power-up, it can still
beusedwithsuchcells.Suchacellwillbefullyreplenished
by the subsequent trickle charge cycle. Under most con-
ditions, even a partially charged large cell will still be
capable of supporting several hours of backup. For
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LTC1559-3.3/LTC1559-5
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example, a small 60mAhr SAFT cell can back up the
systemfor20minutesatanoutputpowerof100mW.Note
that at VCC = 3.07V (LTC1559-3.3), the boost converter
efficiencyimprovesandallowsmorebackuptimefromthe
same cell compared to VCC = 4.625V (LTC1559-5).
CTL pin. In trickle charge mode, CTL is regulated to 0.5V,
resulting in a CTL pin current of (VBAT – 0.5)/REXT. This
current is internally multiplied to feed back ten times the
R
EXT current into the backup battery. Since the LTC1559
trickle charges only after the completion of the fast
recharge cycle, the backup cell voltage should be very
close to 1.2V. This simplifies the calculation of the REXT
resistor value. For example, a 47k resistor from VBAT to
CTL sets the trickle charge current to 150µA.
Once it reaches full recharge, a cell bigger than 512mAhr
will overrun the gas gauge counter before it runs out of
charge during an extended backup cycle. The LTC1559
gas gauge counter will not roll over if this occurs; it will
stay at full count until the backup cycle ends and then
partially recharge the cell with a full count cycle as above.
Undervoltage Lockout
The LTC1559 includes an undervoltage lockout (UVLO)
circuit that shuts the system down gracefully if the backup
cell is exhausted or overloaded. As described in the
previous section, the LTC1559 terminates backup opera-
tion and remains off until the main power supply returns.
It then runs a fast recharge cycle to recharge the backup
cell. An onboard low-battery comparator in the 16-pin GN
or SO package provides an early warning signal if the
backup cell drops below 1V.
Very short backup cycles (<32s) may not extract enough
charge from the backup cell to increment the gas gauge
counter at all. To ensure that the backup cell is not slowly
“nibbled” away, the gas gauge counter is always
incremented by 1mAhr each time the controller exits
backup. This ensures that the backup cell is replenished
with at least a 1mAhr charge every time the LTC1559
enters backup mode.
Battery Backup Cell Trickle Charge
The UVLO circuit trips if the LTC1559’s VCC supervisory
circuit detects that VCC drops below –9% of the rated VCC
voltage due to overload or output short-circuit conditions.
Once the UVLO circuit trips, the LTC1559 asserts the
RESET and RESET pins until the VCC voltage drops below
1V. It then remains off until VCC rises to within –5.5% of
the rated output voltage (LTC1559-3.3). During power-up
from UVLO, the LTC1559 asserts the RESET and RESET
pins until the VCC(rated value) – 5.5%(LTC1559-3.3)
threshold. Once VCC exceeds VCC(rated value) – 5.5%
(LTC1559-3.3), the RESET and RESET pins remain
asserted for another 200ms (“hard” reset) before being
released to inform the system to start operating.
When the gas gauge counter reaches zero, the LTC1559
terminatesfastrechargeandreducestherechargecurrent
totheuser-programmedtricklecurrentlevel.TheLTC1559
provides a trickle current that the user can program from
50µA to 2mA. The trickle current is set by an external
resistor from the positive terminal of the backup cell to the
V
CC
10I
SW
1.2V
NiCd
CELL
+
I
1µF
R
EXT
Reset Operation
CTL
The LTC1559 includes an onboard push-button reset
switch controller. If the CTL pin is pulled to ground
(<250mV) by a push-button or an open-drain output, the
LTC1559 generates a pulse at the RESET and RESET pins
after the trailing edge of the CTL signal. A short (less than
two seconds) low going signal at CTL generates a “soft”
reset (100µs) pulse at the reset pins. A low CTL signal for
more than two seconds generates a “hard” reset pulse at
the RESET and RESET pins. During “hard” reset, the
1×
11×
–
+
+
0.5V
–
LTC1559
1559 F04
Figure 4. Trickle Current Charger
13
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20ms < t
< 2s
CTL
(A)
0V
(B)
shut off completely. Note that the backup cell slowly
discharges through REXT in this mode.
>0.25V
CTL
t
< 20ms
CTL
Inductor Selection
RESET
100µs
100µs
20ms
The LTC1559 is designed to operate with a recommended
inductorvalueof22µH(±20%)with<0.2ΩDCresistance.
DEBOUNCE
“SOFT” PUSH-BUTTON RESET AT CTL
(A) CTL < 0.25V FOR LESS THAN 20ms
(B) CTL > 0.25V FOR MORE THAN 20ms
Usinginductorvaluesabove22µHwilldelivermoreoutput
power but will cause the gas gauge counter to count
inaccurately and under-recharge the backup cell. At the
same time, the N-channel transistor timer will limit the
peak current if the charging time becomes overextended
due to the higher inductor value. Using inductor values
lower than 22µH will degrade the boost converter’s maxi-
mum output power and cause the gas gauge counter to
overcharge the backup cell. Table 3 lists a few recom-
mended surface mount inductor part numbers.
>0.25V
0V
CTL
t
> 2s
CTL
RESET
2s
200ms
“HARD” PUSH-BUTTON RESET AT CTL
CTL < 0.25V FOR MORE THAN 2s
0V
CTL
20ms
RESET
Table 3. Recommended Inductors
20ms
PART
NUMBER
TYP INDUCTOR
VALUE
DCR
(Ω)
1559 F05
20ms DEBOUNCE AT FALLING AND RISING RESET EDGE
MANUFACTURER
Sumida
CD54-220
22µH ±20%
22µH ±20%
0.18
Figure 5. Push-Button Resets
Sumida
CDRH73/74
0.2/0.11
LTC1559 disables the boost converter if it is in backup
mode. All signals at the CTL pin are debounced for 20ms
to prevent multiple resets, allowing the CTL pin to be
connected directly to a push-button to ground.
Capacitor Selection
The LTC1559 requires a VCC capacitor of 100µF to ensure
that boost converter can regulate the output under maxi-
mum load conditions. The capacitor’s ESR should be
small (<0.2Ω) to minimize voltage spikes that might
incorrectly trigger the LTC1559’s internal VCC compara-
tors. Note that the LTC1559 can usually share the output
capacitor with the system regulator. However, a 1µF is
recommended directly at the LTC1559’s VCC pin. The VCC
capacitor’s ratings like VMAX, IRIPPLE(RMS) all must meet
the system regulator’s specifications as well.
The RESET pin is an open-drain output that requires an
external pull-up resistor. The RESET pin is a TTL compat-
ible CMOS output.
Shutdown
The 16-pin LTC1559 has a TTL compatible input, SHDN
that shuts down the whole chip, asserts the RESET and
RESET pins and places the CTL, VBAK and SW pins into
high impedance states. The SHDN pin has an internal pull-
upof8µAthatensuresthechipwillnotshutdownifthepin
is left floating. The chip consumes less than 50µA during
shutdown.
Battery Selection
A primary application for the LTC1559 is a “bridging”
supply, only providing backup current while the main
system battery is being replaced. In these applications,
the LTC1559 works well with NiCd button cells or small
cylindricalcells, reducingsystemcostsandboardspace.
It is optimized for use with up to 512mAhr battery
capacities.
Although there is no SHDN pin for the SO-8 package, the
user can shut down the part by pulling CTL to ground. The
chip enters “hard” reset leaving only the bandgap and
comparators alive. The charger and the boost converter
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Table 4. Button/Cylindrical NiCd 1.2V Cells
The LTC1559 works with standard or memory backup
specific NiCd cells. Memory backup cells can operate at
higher temperatures and have lower self-discharge rates.
The LTC1559’s trickle charger is designed to accommo-
date both memory backup cells (with low self-discharge)
and standard cells (with higher self-discharge). Some
recommendedmanufacturersandpartnumbersarelisted
in Table 4.
MANUFACTURER
(TYPE)
PART
NUMBER
CAPACITY
(mAhr)
R
SERIES
(Ω)
SAFT
(Memory Backup)
GB60
GB170
GB280
60
170
280
1.1
0.4
0.4
SAFT
(Standard)
VB10E
VB22E
VB30E
VB60E
100
220
300
600
0.038
0.022
0.017
0.014
The internal resistance of the backup cell increases power
dissipation as the boost converter draws current from it
during switching, degrading efficiency. Due to the fixed
inductor peak current architecture, the LTC1559’s boost
converter output power drops significantly when the NiCd
cell’s internal resistance increases at the end of its charge.
The inductor charging time increases due to a larger R/L
time constant, decreasing the switching frequency. It is
advisable, especially for batteries with high internal resis-
tance, to include a 1µF or larger bypass capacitor across
the battery to ensure that the boost converter can deliver
the maximum output power regardless of the NiCd inter-
nal resistance.
Sanyo
(Standard)
N-50AAA
N-110AA
N-120TA
N-150N
N-200AAA
N-270AA
N-500A
55
120
130
170
220
305
500
0.055
0.03
0.034
0.027
0.021
0.015
0.09
Panasonic (Standard)
P-11AA
110
0.08
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TYPICAL APPLICATION
LTC1559-3.3 Backup System with an LTC1435 Main System Regulator (LTC1435 Output Sense at the Drain of Q11)
†
L11
22µH
1
SW
8
BACKUP
BATTERY
1.2V
+
C11
1µF
6.3V
R14
14k
V
BAK
7
V
CC
+
NiCd
3
C12
1µF
R15
100k
CTL
LTC1559-3.3
RESET
2
4
5
6
GND
RESET
RESET
PUSH-BUTTON
PS
BACKUP
BACKUP
C
IN
Q1
MAIN
BATTERY
4.5 TO 28V
+
C2
22µF
35V
× 2
N-CHANNEL
Si4412DY
0.1µF
13 16
TG
SW
V
EXTV
IN
14
15
9
4
CC
MAIN
OUTPUT
3.3V
SFB
BOOST
LTC1435
INTV
C4
0.1
Q11
P-CHANNEL
Si9424Y
D1
CMDSH-3
L1*
R
SENSE**
µF
10µH
BACKUP
OUTPUT
3.3V
0.033Ω
6
3
12
8
V
OSENSE
CC
+
C
+
OUT
+
C15
100µF
10V
I
SENSE
TH
C5
1000pF
100µF
10V
C
C
2
1
7
–
RUN/SS SENSE
330pF
×2
Q2
R1
35.7k
1%
11
C6
C
BG
SGND PGND
N-CHANNEL
Si4412DY
OSC
C3
100pF
+
D2
4.7
µF
C
C
0.1
MBRS140T3
C2
SS
µ
16V
5
10
51pF
F
*SUMIDA CDRH125-10
R
R5
20k
1%
C
OSC
68pF
**IRC LR2010-01-R033-F
C
†
10k
SUMIDA CD54-220
1559 TA03
C1
100pF
Description
during backup mode, the LTC1559 deasserts its BACKUP
pin and returns control back to the LTC1435. Q11 turns on
and allows the LTC1435 to charge C15. Please refer to the
Applications Information section for more details.
ThePSpinconnectstoQ11’sdrainandallowstheLTC1559
to detect the restoration of the main battery during backup
mode. Once the LTC1435’s output is greater than VOUT
16
LTC1559-3.3/LTC1559-5
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
7
5
8
6
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
3
4
2
0.010 – 0.020
(0.254 – 0.508)
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.050
(1.270)
TYP
0.014 – 0.019
(0.355 – 0.483)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
SO8 0996
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
17
LTC1559-3.3/LTC1559-5
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
GN Package
16-Lead Plastic SSOP (Narrow 0.150)
(LTC DWG # 05-08-1641)
0.189 – 0.196*
(4.801 – 4.978)
16 15 14 13 12 11 10
9
0.229 – 0.244
(5.817 – 6.198)
0.150 – 0.157**
(3.810 – 3.988)
1
2
3
4
5
6
7
8
0.015 ± 0.004
(0.38 ± 0.10)
× 45°
0.053 – 0.068
(1.351 – 1.727)
0.004 – 0.0098
(0.102 – 0.249)
0.007 – 0.0098
(0.178 – 0.249)
0° – 8° TYP
0.016 – 0.050
(0.406 – 1.270)
0.008 – 0.012
(0.203 – 0.305)
0.025
(0.635)
BSC
*
DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
GN16 (SSOP) 1197
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
18
LTC1559-3.3/LTC1559-5
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S Package
16-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.386 – 0.394*
(9.804 – 10.008)
16
15
14
13
12
11
10
9
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
5
7
8
1
2
3
4
6
0.010 – 0.020
(0.254 – 0.508)
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0° – 8° TYP
0.050
(1.270)
TYP
0.014 – 0.019
(0.355 – 0.483)
0.016 – 0.050
0.406 – 1.270
S16 0695
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
19
LTC1559-3.3/LTC1559-5
U
TYPICAL APPLICATION
LTC1559-3.3 Backup System with an LTC1435 Main System Regulator
(LTC1435 Output Sense at the Source of Q11, LTC1559’s PS Pin Is Grounded)
†
L11
22µH
1
SW
8
BACKUP
BATTERY
1.2V
+
C11
1µF
6.3V
R14
14k
V
BAK
7
V
CC
+
NiCd
3
C12
1µF
R15
100k
CTL
LTC1559-3.3
RESET
2
4
5
6
GND
RESET
RESET
PUSH-BUTTON
PS
BACKUP
BACKUP
C
IN
Q1
MAIN
BATTERY
4.5 TO 28V
+
C2
22µF
35V
× 2
N-CHANNEL
Si4412DY
0.1µF
13 16
TG
SW
V
EXTV
IN
14
15
9
4
CC
SFB
BOOST
LTC1435
INTV
C4
0.1
Q11
P-CHANNEL
Si9424DY
D1
CMDSH-3
L1*
R
SENSE**
0.033Ω
µF
10
µH
6
3
12
8
V
OUT
3.3V
V
OSENSE
CC
+
C
OUT
+
100µF
10V
I
SENSE
TH
C5
1000pF
C
C
2
1
7
×2
–
RUN/SS SENSE
330pF
D2
Q2
N-CH
Si4412DY
11
R1
35.7k
1%
MBRS140T3
C
BG
SGND PGND
OSC
C6
100pF
C3
+
4.7
µF
C
C
0.1
C2
SS
µ
5
10
16V
51pF
F
R5
C
R
OSC
C
20k
1%
68pF
10k
*SUMIDA CDRH125-10
**IRC LR2010-01-R033-F
†
SUMIDA CD54-220
1559 TA04
C1
100pF
Description
batteryisrestored.Thus,theLTC1559doesnotusethePS
pin to sense the LTC1435’s output during backup mode.
The PS pin is grounded in this case. Please refer to the
Applications Information section for more details.
With its SENSE pin at the source of Q11, the LTC1435 can
raise VOUT above VCC(rated voltage) – 5.5% once the main
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC690/LTC691 Microprocessor Supervisory Circuits
LTC694/LTC695
Microprocessor Power Supply Monitor and Backup with Power Fail
Comparator
LTC699
Microprocessor Supervisory Circuits
Microprocessor Supervisory Circuits
Microprocessor Supervisory Circuits
Microprocessor Power Supply Monitor and Backup
Include Push-Button Reset
LTC1232
LTC1235
LTC1149
Include Push-Button Reset and Power Fail Comparator
High Efficiency Synchronous Step-Down
Switching Regulator
V
IN
up to 48V, Burst ModeTM Operation
LTC1435
LTC1479
LTC1558
High Efficiency, Low Noise Synchronous
Step-Down Switching Regulator
Ultrahigh Efficiency, Burst Mode Operation
PowerPathTM Controller for Dual
Battery Systems
Complete Power Management Controller for Battery
Notebook Computers and Other Portable Equipment
Battery Backup Controller with
Programmable Output
Similar to LTC1559 Except That It Backs up the Main System Regulator’s
Input, Allowing Backup of Multiple Output Voltages
PowerPath and Burst Mode are trademarks of Linear Technology Corporation.
1559f LT/TP 1098 4K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1998
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
20
●
●
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
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