LTC1558CS8-5 [Linear]
Backup Battery Controller with Programmable Output; 具有可编程输出备用电池控制器
| 型号： | LTC1558CS8-5 |
| 厂家： | 
Linear |
| 描述： | Backup Battery Controller with Programmable Output |
| 文件： | 总20页 (文件大小：358K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC1558-3.3/LTC1558-5
Backup Battery Controller
with Programmable Output
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FEATURES
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. Theboostconverterusesasynchronousswitching
architecture to achieve a typical efficiency of 70%, ensur-
ing maximum backup lifetime from a small NiCd cell.
■
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
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.
Maximizes System Efficiency After Backup
■
On-Chip Power-On Reset
■
Pushbutton Reset Input
Reset Assertion Guaranteed at VCC = 1V
Short-Circuit Protection
Thermal Limiting
■
■
■
The LTC1558’s automatic backup switching architecture
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 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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TYPICAL APPLICATION
L1
Backup Time
22µH*
vs 3.3V Output Load Current
1.2V
LTC1558-3.3
+
+
NiCd
BACKUP
C2
0.1µF
C1
R1
14k
R2
100k
8
7
6
5
1
2
3
4
450
SW
V
BAK
1µF
V
V
= 3.3V
BAK
NiCd CELL
CC
**BATTERY
= 3.78V
400
350
300
250
GND
V
CC
CAPACITY = 110mAHrs
CTL BACKUP
FB RESET
SYSTEM
µP
RESET
S1
200
150
100
50
R3
220k
C
Q1
Si4431DY
IN
V
CC
3.3V
MAIN
+
R4
†
LOAD CURRENT
100µF
LTC1435
SYNCHRONOUS
BUCK REGULATOR
BATTERY
221k
3A AT NORMAL MODE
16V
×2
4.5V TO 10V
1%
30mA AT BACKUP MODE
0
1558 TA01
R5
100k
1%
0
15
20
25
30
5
10
*SUMIDA CD54-22µH
**SANYO CADNICA N-110AA
CONSULT LTC1435 DATA SHEET FOR
CIRCUIT APPLICATION INFORMATION
LOAD CURRENT (mA)
†
1558 TA02
1
LTC1558-3.3/LTC1558-5
W W
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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
V
BAK, BACKUP ..................................................... 12V
SW ...................................................................... 14V
All Other Pins .................................. –0.3V to VCC + 0.3V
Input Currents (SW)........................................... 500mA
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PACKAGE/ORDER INFORMATION
TOP VIEW
ORDER PART
ORDER PART
NUMBER
SW
SW
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
V
V
V
NUMBER
BAK
BAK
CC
TOP VIEW
LTC1558CS8-3.3
LTC1558CS8-5
LTC1558CGN-3.3
LTC1558CGN-5
LTC1558CS-3.3
LTC1558CS-5
1
2
3
4
8
7
6
5
SW
GND
CTL
FB
V
V
PGND
GND
CTL
BAK
BACKUP
RESET
RESET
NC
CC
BACKUP
RESET
SHDN
FB
S8 PART MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 130°C/ W
NC
LOBAT
155833
15585
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
CC
Operating Voltage Range
LTC1558-3.3
LTC1558-5
●
●
2.90
4.40
3.465
5.250
V
V
V
V
Backup Battery Cell Voltage
●
●
●
1.0
1.2
1.5
V
V
BAT
REF
VCC
BAT
Internal Reference Voltage
1.247 1.272 1.297
I
I
Quiescent Supply Current (Note 2)
Peak Inductor Current (Backup Mode)
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
I
I
Battery Standby Current
V
= 0V
CC
●
●
●
●
●
●
●
0.1
15
50
µA
µA
%
%
%
%
V
BAT(SHDN)
VCC(SHDN)
Supply Current During Shutdown (Note 3)
Backup Request Trip Point
V
V
V
V
V
Voltage at V Relative to V
–10.5 –7.5
–10.5 –7.5
–5.5
–5.5
–4
BAK(ON)
BST(ON)
BAK(OFF)
BST(OFF)
LOBAT
FB
REF
REF
REF
REF
Boost Converter Assertion Trip Point
Backup Deassertion Trip Point
Boost Converter Deassertion Trip Point
Voltage at V Relative to V
FB
Voltage at V Relative to V
–9
–10.5 –7.5
0.95
–6
FB
Voltage at V Relative to V
–5.5
1.05
FB
Low V
Detect (Note 3)
1
BAT
2
LTC1558-3.3/LTC1558-5
ELECTRICAL CHARACTERISTICS VBAT = 1.2V, TA = 0°C to 70°C unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
V
V
V
V
UVLO Trip Voltage (Note 4)
LTC1558-3.3
LTC1558-5
●
●
2.90
4.40
3.00
4.55
3.10
4.70
V
V
UVLO(ON)
UVLO(OFF)
LOBAT
CC
UVLO Recovery Trip Voltage (Note 4)
LTC1558-3.3
LTC1558-5
●
●
3.00
4.55
3.10
4.70
3.20
4.85
V
V
CC
UVLO Trip Voltage (Note 5)
●
0.85
0.9
0.95
V
BAT
Backup Battery Charger
I
I
Battery Charge Current
Fast Recharge
●
11
0.05
1.35
8
16
21
2
mA
mA
C/C
A/A
V
CHGF
CHGT
Programmable Trickle Charge Current Range
Fast Recharge Factor (Note 6)
Q
Q
1.6
10
1.85
12
RECH
Nominal Trickle Charge Multiplier Factor
Trickle Charge Clamp Voltage
I
I
= 1mA
= 1mA
TRK
CHGT
CHGT
V
●
0.45
0.5
0.55
CTL(CLAMP)
Pushbutton Reset
V
CTL Input Threshold
250
mV
ms
CTL
CTL
t
CTL Input Low Time (Debounce Time)
20
Reset Timer
t
t
Pushbutton Duration for Hard Reset
RESET Pulse Width
1.10
1.8
3.4
s
HRESET
RST
V
V
Low for <t
Low for >t
(Soft Reset)
(Hard Reset)
●
●
50
115
80
185
150
345
µs
ms
CTL
CTL
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
CC
CC
= 4.25V, I
= 1.6mA
0.1
RST
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
Internal V Monitor Comparator
CC
t
V
Comparator Propagation
∆V = –(9% V + 300mV), V = 300mV
9
µs
PLH
UVLO(ON)
CC
CC
OD
Delay (Rising)
Shutdown Pin (Note 3)
V
SHDN Input Threshold
SHDN Pin Bias Current
Logic Low, V
●
●
0.8
15
V
V
SHDN
IL
IH
Logic High, V
2
I
V
= 5V, V
= 0V
SHDN
●
8
1
µA
SHDN
CC
Feedback Pin
I
FB Pin Bias Current
10
nA
FB
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 pushbutton reset.
Note 3: Only applies to 16-pin version.
Note 4: Thresholds will track each other and are guaranteed not to overlap.
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
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TYPICAL PERFORMANCE CHARACTERISTICS
Boost Converter Switching
Frequency
Output Power vs Battery Voltage
Backup Time vs Battery Capacity
150
125
3.0
2.5
125
100
75
50
25
0
V = 5V (LTC1558-5)
CC
V = 6V
BAK
V
V
P
= 1.2V
V
V
I
= 1.2V
= 3.3V (LTC1558-3.3)
= 330mA
BATT
BAK
OUT
BATT
CC
PK
= 6V
= 100mW
100
75
2.0
1.5
50
25
0
1.0
0.5
0
1.0
1.1
1.2
1.3
1.4
0
125
250
375
500
6
2
4
8
10
NiCd TERMINAL VOLTAGE (V)
NiCd CELL CAPACITY (mAHr)
OUTPUT VOLTAGE, V
(V)
BAK
1558 G01
1558 G02
1558 G03
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
10.5
10.0
9.5
100
80
60
40
20
0
V
= 1.2V
BATT
9.0
0.970
0.965
8.5
V
V
PK
= 1.2V
= 3.3V (LTC1558-3.3)
= 330mA
0.960
0.955
0.950
BATT
CC
8.0
I
7.5
75
4
6
8
0.05
0.1
1
2
0
25
50
2
10
TEMPERATURE (°C)
NiCd BATTERY TRICKLE CURRENT (mA)
OUTPUT VOLTAGE, V
(V)
BAK
1558 G05
1558 G06
1558 G04
RESET Output Voltage
vs Supply Voltage
Fast Recharge Time (Assume
Fully Exhausted NiCd Battery)
RESET Output Voltage
vs Supply Voltage
60
50
40
30
20
10
0
6
5
4
3
2
1
0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
V
= 5V (LTC1558-5)
V
CC
= 3.3V (LTC1558-3.3)
CC
3.10V
3V
4.7V
4.55V
64
128
256
512
0
2
3
4
5
6
0
2
3
4
1
1
BATTERY CAPACITY (mAHr)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
1558 G07
1558 G08
1558 G09
4
LTC1558-3.3/LTC1558-5
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PIN FUNCTIONS
Pin Numbers are Shown First for the SO-8 Package
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.
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
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.
BACKUP(Pins6/13): BackupActive. Thisisanopen-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.
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.
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 VCC to ground.
The UVLO detector inside the LTC1558 monitors VCC.If
VCC 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 VCC rises
to greater than –6% of the rated output voltage. See the
Applications Information section for more details.
CTL (Pins 3/5): Control. This pin provides three functions.
Inbackupmodethispinentersahighimpedancestateand
monitors the backup battery cell voltage (VBAT). If VBAT
drops below 0.9V, the LTC1558 enters into UVLO. During
trickle charge mode, an external resistor REXT 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.
VBAK(Pins8/15,16):BackupSupplyOutput.TheLTC1558’s
boost converter provides regulated output voltage to the
system through VBAK during backup mode.
FB (Pins 4/7): Output Voltage Feedback. This pin is fed to
theLTC1558’sinternalcomparators.Theboostconverter’s
output voltage is set with an external resistor divider
connected from VBAK to FB. The LTC1558 enters backup
mode when FB drops 7.5% below the internal reference
voltage (VREF). During backup, the boost converter runs
whenever FB drops below this (VREF – 7.5%) threshold.
The LTC1558 exits backup mode when FB rises above
(VREF – 6%).
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 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 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 VCC is greater
than or equal to 1V.
5
LTC1558-3.3/LTC1558-5
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PIN FUNCTIONS
LOBAT (Pin 9): Low-Battery Detector Output. This is an
open-drain output that pulls low when the backup cell
drops below 1V. It gives early warning to the system
controller that the backup cell is getting weak. This pin is
disabled when the LTC1558 is in trickle charge mode.
RESET (Pin 12): System Reset, Active High. This is a TTL-
compatible output driver. It can be used to connect to
systems that require active high logic. The RESET output
will go high whenever RESET is pulled low. If RESET is
externally pulled low, RESET will go high.
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BLOCK DIAGRAM
P1
SW
V
BAK
V
/V
CC BAK
N1
CHARGER
CTL
FB
BOOST/BACKUP
LOGIC
+
–
BACKUP
RESET
RESET
LEVEL SENSE
AND DEBOUNCE
RESET
GENERATOR
V
REF
V
CC
V
REF
GAS GAUGE
+
–
–
+
LOBAT
UVLO
DETECTOR
THERMAL
LIMIT
SHUTDOWN
LOGIC
BANDGAP
= 1.272V
SHDN
V
REF
1558 BD
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SWITCHING WAVEFORMS
Simplified LTC1558 Connections in a
Battery Backup System
Cold Power Boot-Up (Main Battery Replaced/Turned On)
TO
SYSTEM
CONTROL
RATED BATTERY TERMINAL VOLTAGE
1.2V
NiCd
SW
1
BACKUP RESET
LTC1558
BAK
2
3
4
RATED V VOLTAGE
CC
V
BAT
V
–6%
FB
V
CC
V
BAK
V
IN
+
Q
MULTIPLE
POWER
EXT
MAIN SYSTEM
REGULATOR
R1
R2
V
CC
C
IN
V
200ms
BAT
MAIN
BATTERY
OUTPUTS
RESET
FOR MORE DETAILED APPLICATION SCHEMATICS
PLEASE REFER TO THE TYPICAL APPLICATIONS SECTION
BACKUP
1558 SW01
1558 SW02
6
LTC1558-3.3/LTC1558-5
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SWITCHING WAVEFORMS
Cold Power Boot-Up Description
3. The LTC1558’s internal bandgap wakes up. The
LTC1558’s internal boost converter does not turn on as
RESET remains asserted. Once VFB is greater than
(VREF – 6%), BACKUP is deasserted after the tPHL delay
1. The VBAT voltage increases and turns on the QEXT body
diode. VBAK follows VBAT by one body diode drop.
2. VBAK increases above the system regulator’s minimum
input voltage. The system regulator wakes up and
starts ramping up the system power supply. RESET
remains asserted from VCC = 1V.
time. QEXT turns on and VBAK = VBAT
.
4. RESET is asserted for a further 200ms after VCC
exceeds –6% of its rated value.
Backup Mode (Main Battery Discharged)
1V
1.2V
0.9V
V
NICD
BOOST CONVERTER OUTPUT
–7.5%
–6%
–7.5%
–7.5%
V
FB
t
t
FALL
RISE
BACKUP
INDUCTOR
CURRENT
t
t
RISE
RISE
RESET
LOBAT
t
RISE
1
2
3
4
1558 SW03
Backup Mode Description
3. Recovery from Backup Mode. While the boost con-
verter is running, the main battery is restored. This
causes the external MOSFET’s body diode to conduct
and VFB is pulled higher than (VREF – 6%). BACKUP
deassertsandtheboostconverterfinishesitslastcycle.
1. Trigger into Backup Mode. The main battery fails and
VFB drops7.5%belowtheLTC1558’sinternalVREF.The
BACKUP pin is asserted after a tRISE delay time and the
LTC1558’s boost converter is turned on.
4. Trigger into UVLO. During backup, the 1.2V NiCd cell
grows weak and its terminal voltage falls. The LOBAT
pin is asserted to give an early warning when the cell
voltage drops below 1V. RESET is asserted when the
cell voltage drops below 0.9V and the LTC1558 enters
UVLO mode.
2. BackupMode. TheLTC1558’sboostconvertercharges
and discharges the inductor with 165mA peak current.
If VFB doesn’t recover above (VREF –7.5%) (due to a
heavy load), the boost converter increases peak charg-
ing current to 330mA. When VFB rises above
(VREF – 7.5%), the boost converter stops but the
BACKUP pin remains asserted.
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LTC1558-3.3/LTC1558-5
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APPLICATIONS INFORMATION
Table 1
OPERATING MODES
Overview
CONDITIONS
1V < V < V (Rated Value) – 9%
The LTC1558 is a versatile backup battery control system
designed to provide all the functions necessary to imple-
ment a complete, highly integrated backup system within
a single chip. It allows the system to maintain its rated
supply voltage during backup, offering maximum system
designflexibility.TheLTC1558allowstheuseofalowcost
rechargeableNiCdcellforbackup,eliminatingtheneedfor
expensive, replaceable 4.5V lithium backup cells.
UVLO Reset
CC
CC
or V
< 0.9V
BAT
Pushbutton Reset
UVLO Reset Recovery
Backup Mode Activation
Backup Mode Exit
V
< 250mV
CTL
V
> V (Rated Value) – 6%
CC
CC
V
< (V –7.5%)
REF
FB
V
> (V – 6%)
REF
FB
Boost Converter Activation
Boost Converter Deactivation
V
V
< (V –7.5%)
REF
FB
FB
> (V –7.5%)
REF
The LTC1558 includes an onboard boost converter de-
signed to generate an adjustable voltage (3V to 10V) from
a single 1.2V NiCd cell. This voltage is connected to the
system’s DC/DC converter input, enabling the system to
continue operation when the main battery 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 externally
adjustable trickle charge circuit maintains the cell charge
after the fast charge cycle has completed, minimizing
drain from the main battery during standby.
backup. It can supply a minimum backup power of
100mW.Theboostconverteroperatesinamodifiedpulse
skipping mode; each switch cycle transfers a known
amount of charge from the backup cell to the regulated
output.Thispreventsuncontrolleddischargeofthebackup
cell and allows the LTC1558 to accurately measure the
charge removed from the backup cell by counting the
charge pulses.
TheLTC1558entersbackupmodewhenthemainbattery
voltage drops. As shown in Figure 1, the main battery
voltage is scaled down by an external resistor divider and
fed to the LTC1558’s backup comparators. These com-
pare the scaled voltage with an internal trimmed VREF
(1.272V), switching the LTC1558 into backup mode
when VFB drops 7.5% below VREF. Upon entering backup
mode, the BACKUP pin is asserted and the internal boost
converterturnson. TheBACKUPsignalisusedtoturnoff
the external P-channel MOSFET, isolating the main bat-
tery from the LTC1558 and the system regulator’s input.
The LTC1558’s boost converter will charge the input
capacitor CIN of the system regulator until VFB rises
above (VREF –7.5%).
Included in the LTC1558 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 LTC1558 also performs VCC supervisory functions
during normal system operations. An LTC1558-3.3 moni-
tors a 3.3V supply voltage at its VCC pin whereas an
LTC1558-5 monitors a 5V supply at its VCC pin. In both
cases, the LTC1558 derives power for the majority of the
internal circuitry (except for the boost converter) from the
VCC pin. Table 1 shows the signal conditions for the
LTC1558’s various operating modes. Note that VCC in
Table 1 refers to the rated VCC voltage, 3.3V or 5V.
TO SYSTEM REGULATOR INPUT
LTC1588
V
Boost Converter Operation
BAK
+
BOOST
MAIN
BATTERY
C
CONVERTER
IN
R1
FB
The LTC1558 uses an onboard synchronous boost con-
verter with a fixed peak current architecture that provides
asimpleandflexiblesystemsolutionwhileeliminatingthe
needforconventionalfrequencycompensation.Theboost
converter’s output, set by the external divider connected
to the FB pin, supports the main system regulator during
BACKUP
LOGIC
BACKUP
R2
V
REF
1558 F01
Figure 1. Typical LTC1558 Connection
8
LTC1558-3.3/LTC1558-5
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Once VFB rises above (VREF –7.5%), the LTC1558’s boost
converter deactivates and the freshly charged input
capacitor supplies power to the system regulator. The
cycle repeats again when the input capacitor’s charge is
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 VFB exceeds the (VREF –7.5%) boost
threshold, the LTC1558 stops the boost converter and
resets the internal two pulse counter. The next time VFB
falls below (VREF –7.5%), the boost converter restarts in
low current mode for at least two boost cycles. Moderate
or changing loads will cause the LTC1558 to shift between
the two peak inductor current limits, keeping the output in
tight regulation. Near its maximum load capability, the
LTC1558 will stay in 330mA high current mode and the
output voltage VBAK will hover around the user pro-
grammed value.
drained away and VFB again drops below (VREF – 7.5%)
.
The BACKUP pin remains asserted until the main battery
isrestored.ThisensuresthattheLTC1558doesnotswitch
in and out of backup mode unnecessarily.
The LTC1558’s boost converter minimizes output ripple
under light load conditions by reducing the charge trans-
ferred for the first two consecutive switch cycles. When
V
FB falls below (VREF –7.5%), the boost operation starts
by connecting the SW pin to ground through an internal
0.5Ω N-channel MOSFET (N1 in the Block Diagram). The
current through the external 22µH inductor rises linearly
through this switch.
VBAK Capacitor ESR
330mA
(PEAK)
The type of output capacitor and the user programmed
VBAK value will affect the LTC1558’s output ripple and
efficiency. In most applications, the main VBAK capacitor
is primarily determined by the requirements of the main
power supply. Such a capacitor will generally meet the
requirements of the LTC1558. In unusual circumstances
or circuits where the main system regulator’s input ca-
pacitor is located some distance away from the LTC1558,
a local output capacitor may be necessary.
165mA
(PEAK)
1558 F02
LIGHT CURRENT MODE
HEAVY CURRENT MODE
Figure 2. Inductor Current During Switching
When the switch current reaches an internally preset level
of 165mA, the boost converter connects the SW pin to the
VBAK pinthroughaninternal2Ω P-channelMOSFET(P1in
the Block Diagram). The inductor current discharges
through P1, charging up the capacitor connected exter-
nally to VBAK (CIN 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 LTC1558 looks at the FB pin voltage.
If VFB has increased above the (VREF –7.5%) threshold,
the boost converter shuts off both switches and waits for
VFB to drop below (VREF –7.5%) again.
1
BOOST
CYCLE
V
BAK
ESR RIPPLE
1588 F03
DISCHARGE
PERIOD
CHARGE
PERIOD
CH
t
t
DISCH
Figure 3. VBAK Ripple
The maximum ripple on the VBAK pin is equal to capacitor
ESR voltage drop due to the boost converter’s output
current pulses. The ripple frequencyandoutput 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
If VFB is still less than (VREF –7.5%) after the first boost
cycle,theLTC1558immediatelyreconnectsSWtoground,
repeating the boost cycle. If after two consecutive pulses,
VFB is still not above the boost threshold (VREF –7.5%)
the LTC1558 decides that the load is not so light after all,
,
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LTC1558-3.3/LTC1558-5
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proportional to the difference between VBAK (3V to 10V)
and the battery cell voltage, VBAT (1.2V).
battery by watching for VFB to exceed (VREF –6%). The
LTC1558 then stops its internal boost converter and
begins to recharge the NiCd cell. BACKUP is deasserted to
signal to the system controller to restore system loading
and resume normal operations. At the same time, the
external P-channel MOSFET is driven by the BACKUP
signal. The P-channel MOSFET turns on and allows the
mainbatterytobypassitsbodydiodeanddrivethesystem
regulator directly.
Assuming ESR = 0.2Ω, IIND(PEAK) = 330mA, VBAK = 6V,
VRIPPLE(P-P) = (IIND(PEAK))(RESR(CAP)
= (330mA)(0.2Ω)
)
= 66mV
Since VBAK must be scaled down to VFB, the external
resistor ratio
Sincetheusercanreplacethemainbatteryanytimeduring
the LTC1558’s backup operations, the BACKUP signal
may be deasserted while the boost converter is switching.
To prevent the potential problem of residual energy in the
inductor, the LTC1558 will only stop the boost converter
after it has completed the current boost cycle.
= 6V/1.272V
= 4.717
Therefore the noise amplitude seen by the FB compara-
tors is:
= 66mV/4.717
= 14mV
UVLO Lockout Under Excessive Backup Load
Very heavy loads (above the LTC1558’s maximum power
output) will pull the boost converter’s output below the
boost threshold. Under these conditions, the LTC1558’s
boost converter will continue to supply 330mA current
pulses to the system regulator while charge on the VBAK
capacitor (CIN) drains away. The system regulator will not
maintain its output regulation and the system VCC will
drop. When VCC drops below –9% of the rated voltage for
more than 9µs, the LTC1558’s VCC supervisory circuit
activatesUVLOmode,shuttingofftheboostconverterand
asserting the RESET pins. The 9µs delay prevents the
LTC1558 from being fooled by brief transients or noise
spikes on its VCC pin. Upon receipt of the reset signals, the
host system should shut down in a orderly manner. The
LTC1558’s VCC supervisory circuit will remain alive until
VCC is less than 1V to ensure valid reset pin signals.
The discharge time period,
tDISCH = (L • IIND(PEAK))/(VBAK – VBAT
)
= (22µH • 330mA)/(6V – 1.2V)
= 1.5µs
For lowest VBAK = 3V and maximum IIND(PEAK) = 445mA,
VRIPPLE(P-P) = 89mV
RB resistor ratio = 2.358
Noise amplitude = 37.7mV
tDISCH = 5µs
TheinternalVFB comparatorsaredesignedtohaveaslow
response time to filter away this ripple. The (VREF –6%)
FBcomparatorhasa6µsrisingedgedelayand2µsfalling
edge delay. The (VREF – 7.5%) FB comparator has a
similar 6µs rising time delay but a much longer falling
time delay of 20µs. This enables the comparator to
control the booster properly, and avoids turning off the
boost converter prematurely due to false triggering by
the ESR ripple.
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 LTC1558 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 pins. Since the CTL pin can also be connected
to an external pushbutton reset, the LTC1558 includes
Exit from Backup
When a new battery is inserted into the system, the higher
main battery voltage turns on the external P-channel
MOSFET’s body diode and raises VBAK (and VFB) to a
highervoltage.TheLTC1558detectsthereturnofthemain
10
LTC1558-3.3/LTC1558-5
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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 pushbutton reset (which pulls CTL
below 250mV) from being mistaken as a low cell voltage
condition. Unusual situations where the NiCd cell voltage
dropsdrasticallybelow0.25VwillalsotriggerUVLO,since
the LTC1558 will treat this as a “hard” reset after 2
seconds.
The LTC1558’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.
Backup Cell Fast Recharge
The LTC1558 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 estimate battery
charge by counting switch pulses. The gas gauge counts
up from zero as charge is removed from the backup cell in
backup mode. It takes roughly 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 = 5V, the gas
gauge divider will increment by one count every 7.5µs
while the boost converter is running. Full count is reached
afterapproximately2.2hours,equivalenttoabout512mAhr
of charge.
AnoptionalLOBAToutput,availableinthe16-pinGNorSO
package, can be used to signal the system when the cell
voltage falls below 1V, giving an early warning that the
backup cell is heavily discharged. The LOBAT output is
disabled when the LTC1558 is in trickle charge mode
because the CTL pin is pulled to 0.5V by the LTC1558.
Fault Protection and Thermal Limit
The LTC1558’s boost converter incorporates two internal
timers that turn off the switch transistors if the inductor
charge or discharge time gets abnormally long.
The inductor charge time may get abnormally long if the
NiCdcellvoltagedropsbelow0.25Vwithouttriggeringthe
0.25V < VBAT < 0.9V low cell voltage comparator. In this
case, the NiCd cell is assumed to be damaged and the
LTC1558’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 LTC1558
will enter UVLO either when VCC drops below
(VCC(RATED VOLTAGE) –9%) or after the LTC1558 detects
CTL lower than 0.25V for 2 seconds, in which case “hard”
reset occurs.
Upon entering recharge mode (after the main battery is
restored) the LTC1558 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
gauge counter at a rate designed to replace about 160% of
the charge previously removed from the backup cell.
When the gas gauge counter reaches zero, the LTC1558
reduces the charging current at the SW pin to the user-
programmed trickle charge current level.
The discharging time can also get abnormally long if a
serious overload condition occurs during switching. The
timerwillshutofftheP-channelpasstransistorafter10µs,
protecting the boost converter. The LTC1558 will end up
in UVLO as VCC drops below (VCC(RATED VOLTAGE) –9%).
Under some circumstances, the LTC1558 can exit the
backup mode with invalid gas gauge contents. This can
occur under three possible conditions:
a) The backup cell was completely exhausted during a
backup cycle and the LTC1558 entered UVLO.
In addition, the LTC1558 is protected for safe area opera-
tionwithaninternalthermalshutdowncircuit.Ifthedevice
is overloaded for a long period of time, the thermal
shutdown circuit forces the LTC1558 into UVLO. The
threshold temperature for thermal shutdown is typically
155°C.
b) Thebackupcellwasreplacedwhilethemainsupplywas
disabled.
c) A backup cycle was terminated prematurely by a “hard”
reset or an output overload.
11
LTC1558-3.3/LTC1558-5
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Inthesecases,theLTC1558assumesthatthebackupcell
is exhausted and presets the gas gauge counter to a
default capacity of 128mAhr. It then initiates a recharge
cycle.
Battery Backup Cell Trickle Charge
When the gas gauge counter reaches zero, the LTC1558
terminatesfastrechargeandreducestherechargecurrent
totheuser-programmedtricklecurrentlevel.TheLTC1558
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
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
REXT current into the backup battery. Since the LTC1558
trickle charges only after the completion of the fast re-
charge 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 approximately 150µA.
Setting the gas gauge to this default value results in a fast
rechargecyclelongenoughtoreplenish1.6times128mAhr
of charge 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
will be wasted. However, the LTC1558’s 15mA fast charge
current should not be high enough to damage the cell.
Once the full-count recharge has been completed, the
backupcellisassumedtobefullychargedandsubsequent
backup/recharge cycles resume normally.
Although the LTC1558 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 ex-
ample, a small 60mAhr button cell can back up the system
for 20 minutes at an output power of 100mW. Note that at
lower programmed VBAK values, the boost converter effi-
ciency improves and allows more backup time from the
same cell compared to a higher VBAK value.
V
CC
10I
SW
1.2V
NiCd
CELL
+
I
47µF
R
EXT
CTL
1×
11×
–
Once it reaches full recharge, a cell bigger than 512mAhr
islikelytooverrunthegasgaugecounterbeforeitrunsout
of charge during an extended backup cycle. The LTC1558
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.
+
+
0.5V
–
LTC1558
1558 F04
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
incrementedby1mAhreachtimethecontrollercomesout
of backup. This ensures that the backup cell is always
replenished with at least a 1mAhr charge every time the
LTC1558 enters backup mode.
Figure 4. Trickle Current Charger
Undervoltage Lockout
The LTC1558 includes an undervoltage lockout (UVLO)
system that ensures that the system will shutdown grace-
fully if the backup cell is exhausted or overloaded. As
described in the previous section, the LTC1558 will
12
LTC1558-3.3/LTC1558-5
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terminate backup operation and remain off until the main
power supply returns. It then runs a fast recharge cycle to
recharge the backup cell. An onboard low-battery com-
parator in the 16-pin GN or SO package provides an early
warning signal when the backup cell drops below 1V.
the CTL signal. A short (less than 2s) low going signal at
CTLwillgeneratea“soft”reset(100µs)pulseattheRESET
pins. A low CTL signal for more than 2s will generate a
“hard” reset pulse at its RESETpins. During “hard” reset,
the LTC1558 will disable the boost converter if it is in
backup mode. All signals at the CTL pin are debounced for
20mstopreventmultipleresets,allowingtheCTLpintobe
connected directly to a pushbutton to ground.
The UVLO circuit also trips if the LTC1558’s VCC supervi-
sory circuit detects that VCC drops below –9% of the rated
VCC voltage due to overload or output short-circuit condi-
tions. Once the UVLO circuit trips, the LTC1558 asserts
theRESETpinsuntiltheVCC voltagedropsbelow1V. Itwill
then remain off until VCC rises to within (VCC – 6%) of the
rated output voltage. During power-up from UVLO, the
LTC1558 asserts the RESET pins until the (VCC – 6%)
threshold. Once VCC exceeds (VCC – 6%), the RESET pins
remain asserted for another 200ms (“hard” reset) before
being released to inform the system to start operating.
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 LTC1558 has a TTL-compatible input, SHDN,
that shuts down the whole chip, asserts the RESET pins
andplacestheCTL,VBAK andSWpinsintohighimpedance
states. The SHDN pin has an internal pull-up that ensures
the chip will not shut down if the pin is left floating. The
SHDNpintypicallydraws8µAwhenpulledlowatVCC =5V.
Thechipconsumeslessthan50µAduringshutdownwhile
VCC is still alive.
Reset Operation
TheLTC1558includesanonboardpushbuttonresetswitch
controller. If the CTL pin is pulled to ground (<250mV) by
a pushbutton or an open-drain output, the LTC1558 gen-
erates a pulse at the RESETpins after the trailing edge of
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
shut off completely. Note that the backup cell slowly
discharges through REXT in this mode.
20ms < t
< 2s
CTL
A
0V
B
>0.25V
CTL
t
< 20ms
CTL
RESET
100µs
100µs
20ms
DEBOUNCE
Inductor Selection
“SOFT” PUSHBUTTON RESET AT CTL
A. CTL < 0.25V FOR LESS THAN 20ms
B. CTL > 0.25V FOR MORE THAN 20ms
The LTC1558 is designed to operate with a recommended
inductorvalueof22µH(±20%)with<0.2ΩDCresistance.
>0.25V
0V
CTL
t
> 2s
Using inductor values higher than 22µH will deliver more
output 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 2 lists the recom-
mended surface mount inductor part numbers.
CTL
RESET
2s
200ms
“HARD” PUSHBUTTON RESET AT CTL
CTL < 0.25V FOR MORE THAN 2s
0V
CTL
20ms
RESET
20ms
1558 F05
20ms DEBOUNCE AT FALLING AND RISING RESET EDGE
Figure 5. Pushbutton Resets
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Table 2. Recommended Inductors
Table 3. Button/Cylindrical NiCd 1.2V Cells
PART
NUMBER
TYP INDUCTOR
VALUE
PART
NUMBER
CAPACITY
(mAhr)
MANUFACTURER
Sumida
DCR (Ω)
0.18
MANUFACTURER
R
(Ω)
SERIES
CD54-220
22µH ±20%
22µH ±20%
SAFT
(Memory Backup)
GB60
GB170
GB280
60
170
280
1.1
0.4
0.4
Sumida
CDRH73/74
0.2/0.11
SAFT
(Standard)
VB10E
VB22E
VB30E
VB60E
100
220
300
600
0.038
0.022
0.017
0.014
Capacitor Selection
The LTC1558 requires a minimum VBAK capacitor of 44µF
to ensure that the boost converter can regulate the output
at20mAload.Thecapacitor’sESRshouldbesmall(<0.2Ω)
to minimize voltage spikes that might incorrectly trigger
the LTC1558’s internal FB comparators. Note that the
LTC1558 can usually share the output capacitor with the
Sanyo
(Standard)
N-50AAA
N-110AA
N-120TA
N-150N
N-200AAA
N-270AA
N-500A
55
0.055
0.03
0.034
0.027
0.021
0.015
0.09
120
130
170
220
305
500
system regulator. Thus its ratings like VMAX, IRIPPLE(RMS)
,
Panasonic
(Standard)
P-11AA
110
0.08
etc., will all have to meet the system regulator’s specifica-
tions as well.
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 LTC1558’s boost
converter output power drops significantly when the NiCd
cell’s internal resistance increases at the end of its charge.
This is because the inductor charging time will increase
duetoalargerR/Ltimeconstant,decreasingtheswitching
frequency. Itisadvisable, especiallyforbatterieswithhigh
internal resistance, to include a 47µF bypass capacitor
across the battery to ensure that the boost converter can
deliver the maximum output power regardless of the NiCd
internal resistance.
Battery Selection
A primary application for the LTC1558 is a “bridging”
supply, only providing backup current while the main
system battery is being replaced. In these applications,
the LTC1558 works well with NiCd button cells or small
cylindricalcells, reducingsystemcostsandboardspace.
It is optimized for use with up to 512mAhr battery
capacities.
The LTC1558 can work with standard or memory backup
specific NiCd cells. Memory backup cells can operate at
higher temperatures and have lower self discharge rates.
The LTC1558’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 3.
14
LTC1558-3.3/LTC1558-5
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LTC1558-3.3 Low Main Battery Voltage (4.5V to 10V) Application
L11†
22µH
1
BACKUP
BATTERY
1.2V
+
C11
R14
14k
47µF
SW
7
8
6.3V
V
CC
+
NiCd
3
C12
1µF
CTL
V
BAK
LTC1558-3.3
GND RESET
RESET
PUSHBUTTON
2
4
5
6
RESET
FB BACKUP
BACKUP
R13
100k
MAIN
BATTERY
4.5V TO 10V
R11
221k
1%
Q11
P-CHANNEL
Si4431DY
*SUMIDA CDRH125-10
**IRC LR2D1D-01-RQ33-F
†SUMIDA CD54-220
R12
100k
1%
C
+
IN
+
C2
1µF
22µF
Q1
35V
×2
N-CHANNEL
Si4412DY
13
16
V
IN
TG
9
4
6
3
2
1
14
15
12
8
EXTV
SW
CC
C4
R
L1*
SFB
BOOST
SENSE**
0.1µF
0.033Ω
10
µH
LTC1435
INTV
V
3.3V
3A
OUT
V
OSENSE
CC
+
C
IN
+
D1 CMDSH-3
C5
100µF
I
SENSE
TH
10V
×2
C
C
7
330pF
–
RUN/SS SENSE
BG
R1
C
1000pF
SS
35.7k
1%
11
0.1µF
C
OSC
Q2
D2
C
R
C
OSC
68pF
C2
C
10k
N-CHANNEL
Si4412DY
MBRS140T3
51pF
+
C3
R5
20k
1%
C6
SGND PGND
10
4.7
µ
F
100pF
5
16V
C1
100pF
1558 TA03
Typical “Low Voltage” Application
main battery to turn on the external P-channel MOSFET
and power up the system out of UVLO during cold power
boot or out of backup mode when the LTC1558 is power-
ing up the system.
The maximum main battery voltage is less than the maxi-
mum VBAK pin voltage (12V). This configuration has the
lowest number of external components.
A 100k pull-up resistor enables the open-drain BACKUP
pin to turn the external P-channel MOSFET off when VBAK
is higher than VCC.
The LTC1435’s minimum input voltage is 3.5V. The VBAK
voltage, set by R11 and R12, is programmed to 3.8V.
Therefore, the main battery’s lowest voltage should be
3.8V + 1 body diode drop = 4.5V. This will enable a fresh
15
LTC1558-3.3/LTC1558-5
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TYPICAL APPLICATIONS
LTC1558-5 Medium Main Battery Voltage (7V to 18V) Application
L11†
22µH
1
BACKUP
BATTERY
1.2V
+
C11
R14
14k
47µF
SW
7
8
6.3V
V
CC
+
NiCd
3
C12
1µF
CTL
V
BAK
LTC1558-5
GND RESET
RESET
PUSHBUTTON
2
4
5
6
RESET
FB BACKUP
BACKUP
D11
1N5818
R13
100k
MAIN
BATTERY
7V TO 18V
R11
422k
1%
Q11
P-CHANNEL
Si4431DY
*SUMIDA CDRH125-10
**IRC LR2D1D-01-RQ33-F
†SUMIDA CD54-220
R12
100k
1%
C
+
IN
+
C2
1µF
22µF
Q1
35V
×2
N-CHANNEL
Si4412DY
13
16
V
TG
IN
9
4
6
3
2
1
14
15
12
8
EXTV
SW
CC
C4
0.1
R
L1*
SFB
BOOST
SENSE**
0.033Ω
µF
10
µH
LTC1435
INTV
V
5V
3A
OUT
V
OSENSE
CC
+
C
OUT
+
D1 CMDSH-3
C5
100µF
I
SENSE
TH
10V
×2
C
C
7
330pF
–
RUN/SS SENSE
R1
35.7k
1%
C
1000pF
SS
0.1
11
µ
F
C
OSC
BG
Q2
D2
C
R
C
C2
C
10k
OSC
68pF
N-CHANNEL
Si4412DY
MBRS140T3
51pF
+
C3
R6
11k
1%
C6
100pF
SGND PGND
10
4.7
µ
F
5
16V
C1
100pF
1558 TA04
Typical “Medium Voltage” Application
A 100k pull-up resistor enables the LTC1558’s open-drain
BACKUP pin to turn the external P-channel MOSFET off
during backup mode, even when VBAK is higher than VCC.
The maximum main battery voltage is more than the
maximum VBAK pin voltage (12V). This configuration is
needed for most notebook computers that have 3-cell or
4-cell series connected lithium battery packs.
The main battery pack should have an internal control to
shut itself down once its energy is used up. This prevents
the lithium cells from deep discharge damage. Once the
main battery shuts down, the FB voltage drops and the
LTC1558 switches to backup mode.
The Schottky diode D11 (1N5818) prevents the main
battery’s high terminal voltage from overstressing the
LTC1558’s VBAK pin during nonbackup conditions. An
internal Zener inside the LTC1558 will clamp VBAK to 12V
when the 1N5818’s reverse bias leakage current
increases at high temperature.
16
LTC1558-3.3/LTC1558-5
U
TYPICAL APPLICATIONS
LTC1558-5 High Main Battery Voltage (48V) Application
L11†
22µH
1
BACKUP
BATTERY
1.2V
+
C11
R14
14k
47µF
SW
7
8
6.3V
V
CC
R15
+
NiCd
3
C12
1µF
CTL
V
BAK
100k
D11
MBR170
Q12
LTC1558-5
RESET
2N3906
Z11
RESET
PUSHBUTTON
5
6
RESET
12V
2
GND
BACKUP
BACKUP
R16
100k
FB
4
R11
Q11
P-CHANNEL
MTD2955E
+
C
IN
D1
1N4148
D2
C6
422k
1%
100µF
1N4148
Q1
0.1µF
100V
P-CHANNEL
MTD2955E
MAIN
BATTERY
48V
R12
100k
1%
L1*
68µH
R
**
C2
0.068µF
SENSE
0.04Ω
V
1
16
OUT
PGATE
CAP
5V
2.5A
2
3
4
5
6
7
8
15
V
V
SHUTDOWN 2
IN
C1
0.047µF
14
13
12
11
10
9
C
OUT
+
RGND
CC
220µF
10V
Q2
D3
MBR380
N-CHANNEL
IRFZ34
P-DRIVE
NGATE
LTC1149-5
OS-CON
V
CC
C
T
PGND
SGND
+
C3
3.3µF
C4
470pF
I
SHUTDOWN 1
SHUTDOWN
TH
R3
100Ω
R
C
–
+
1k
SENSE
SENSE
C5
1000pF
R4
100Ω
C
C
3300pF
1558 TA05
*HURRICANE LAB HL-KI168M
**IRC LR2512-01-RO40-5
†SUMIDA CD54-220
Typical “High Voltage” Application
During nonbackup mode, the LTC1558’s open-drain
BACKUP pin is low. The external 12V Zener and 2N3906
conduct and the MTD2955E’s VGS is clamped at approxi-
mately12V. Duringbackup, theBACKUPpinfloatsandthe
2N3906’s base voltage is pushed nearer to VBAK. The
MTD2955E is effectively turned off, isolating the main
battery from VBAK during backup.
The maximum main battery voltage is 48V.
The Schottky diode D11 (MBR170) prevents the main
battery’s high terminal voltage from overstressing the
LTC1558’s VBAK pin during nonbackup conditions. An
internal Zener inside the LTC1558 will clamp VBAK to 12V
when the MBR170’s reverse bias leakage current
increases at high temperature.
The main battery pack should have an internal control to
shut itself down once its energy is used up. This prevents
it from deep discharge damage.
As shown above, the design must ensure that VBAT does
not force the external P-channel MOSFET’s VGS above its
maximum rating (15V for the MTD2955E) shown during
nonbackup mode.
17
LTC1558-3.3/LTC1558-5
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
LTC1558-3.3/LTC1558-5
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
0.053 – 0.069
3
4
2
0.010 – 0.020
(0.254 – 0.508)
× 45°
(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
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
SO8 0996
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
LTC1558-3.3/LTC1558-5
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC690/LTC691
LTC694/LTC695
Microprocessor Supervisory Circuits
Microprocessor Power Supply Monitor and Backup with
Power Fail Comparator
LT®1020
Micropower Linear Regulator
Micropower Linear Regulator
Includes Low-Battery and Dropout Detectors
LT1120
SO-8 Package, Includes Low-Battery Detector
LTC1149
High Efficiency Synchronous Step-Down
Switching Regulator
V
up to 48V, Burst ModeTM Operation
IN
LTC1235
LTC1435
Microprocessor Supervisory Circuit
Includes Pushbutton Reset and Power Fail Comparator
Ultrahigh Efficiency, Burst Mode Operation
High Efficiency, Low Noise Synchronous
Step-Down Switching Regulator
LTC1479
LT1521
PowerPathTM Controller for Dual Battery Systems
Complete Power Management Controller for Battery
Notebook Computers and Other Portable Equipment
Micropower Low Dropout Regulator
300mA, SOT-223 Package
Burst Mode and PowerPath are trademarks of Linear Technology Corporation.
1558f LT/TP 0298 4K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1998
20 Linear Technology Corporation
●
1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900
●
●
FAX: (408) 434-0507 TELEX: 499-3977 www.linear-tech.com
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