LTC1558-3.3/LTC1558-5

Backup Battery Controller

with Programmable Output

Complete Battery Backup System in an
SO-8, 16-Pin GN or SO Package

Generates Adjustable Backup Voltage from a
Single 1.2V NiCd Button Cell

Automatic Main Supply to Backup Switching

Minimum 100mW Output Power

Automatic Fast Recharge of NiCd Battery

Programmable NiCd Trickle Charge Current

Smart NiCd Charger Minimizes Recharge Time and
Maximizes System Efficiency After Backup

On-Chip Power-On Reset

Pushbutton Reset Input

Reset Assertion Guaranteed at V

= 1V

Short-Circuit Protection

Thermal Limiting

FEATURES

DESCRIPTIO

The LTC

1558 is a backup battery controller that provides

all the functions necessary to implement a backup power
supply using a single NiCd cell. It includes a 1.2V boost
converter, an intelligent 2-stage battery charger, auto-
matic backup switching and a microprocessor reset gen-
erator. The boost converter uses a synchronous switching
architecture to achieve a typical efficiency of 70%, ensur-
ing maximum backup lifetime from a small NiCd cell.

The on-chip NiCd charger uses an internal gas gauge to
minimize fast recharge time and prevent overcharging of
the backup cell. The LTC1558 also provides a user pro-
grammable trickle charge current to compensate for self
discharge losses in the backup cell.

The LTC1558's automatic backup switching architecture
requires minimum intervention from the host system and
provides feedback to the host to minimize system loading
in the backup state. Its internal V

fault detector and reset

generator eliminate the need for a separate microproces-
sor supervisory chip in most applications.

The LTC1558 is available in an SO-8, 16-lead GN or SO
package.

APPLICATIO

Notebook Computers

Palmtop Computers/PDAs

Portable Instruments

Battery-Powered Systems

TYPICAL APPLICATIO

, LTC and LT are registered trademarks of Linear Technology Corporation.

LOAD CURRENT (mA)

BACKUP TIME (MINUTES)

150

200

250

350

400

450

1558 TA02

100

300

= 3.3V

BAK

= 3.78V

NiCd CELL
CAPACITY = 110mAHrs

Backup Time

vs 3.3V Output Load Current

C1
1

1.2V

NiCd

BACKUP

**BATTERY

MAIN

BATTERY

4.5V TO 10V

R1
14k

R2
100k

LOAD CURRENT
3A AT NORMAL MODE
30mA AT BACKUP MODE

LTC1558-3.3

R4
221k
1%

R3
220k

R5
100k
1%

RESET

Si4431DY

1558 TA01

BAK

BACKUP

RESET

GND

CTL

SUMIDA CD54-22

SANYO CADNICA N-110AA
CONSULT LTC1435 DATA SHEET FOR
CIRCUIT APPLICATION INFORMATION

100

16V

3.3V

SYSTEM

C2
0.1

LTC1435

SYNCHRONOUS

BUCK REGULATOR

LTC1558-3.3/LTC1558-5

ABSOLUTE

AXI

RATINGS

(Note 1)

Terminal Voltages

CC ..........................................................................................

BAK

, BACKUP ..................................................... 12V

SW ...................................................................... 14V

All Other Pins .................................. 0.3V to V

+ 0.3V

Input Currents (SW) ........................................... 500mA

BAK

Output Current ................... Short-Circuit Protected

Operating Ambient Temperature Range ....... 0

C to 70

Junction Temperature .......................................... 125

Storage Temperature Range .................. 65

C to 150

Lead Temperature (Soldering, 10 sec)................... 300

PACKAGE/ORDER I

FOR

ATIO

ELECTRICAL CHARACTERISTICS

BAT

= 1.2V, T

= 0

C to 70

C unless otherwise noted.

Consult factory for Industrial and Military grade parts.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Battery Backup Switching

Operating Voltage Range

LTC1558-3.3

2.90

3.465

LTC1558-5

4.40

5.250

BAT

Backup Battery Cell Voltage

1.0

1.2

1.5

REF

Internal Reference Voltage

1.247

1.272

1.297

VCC

Quiescent Supply Current (Note 2)

155

250

BAT

Peak Inductor Current (Backup Mode)

Boost Converter in Low Current Mode (Note 7)

165

225

Boost Converter in High Current Mode (Note 7)

225

330

445

BAT(SHDN)

Battery Standby Current

= 0V

0.1

VCC(SHDN)

Supply Current During Shutdown (Note 3)

BAK(ON)

Backup Request Trip Point

Voltage at V

Relative to V

REF

10.5

7.5

5.5

BST(ON)

Boost Converter Assertion Trip Point

Voltage at V

Relative to V

REF

10.5

7.5

5.5

BAK(OFF)

Backup Deassertion Trip Point

Voltage at V

Relative to V

REF

BST(OFF)

Boost Converter Deassertion Trip Point

Voltage at V

Relative to V

REF

10.5

7.5

5.5

LOBAT

Low V

BAT

Detect (Note 3)

0.95

1.05

ORDER PART

NUMBER

LTC1558CGN-3.3
LTC1558CGN-5
LTC1558CS-3.3
LTC1558CS-5

TOP VIEW

S PACKAGE

16-LEAD PLASTIC SO

GN PACKAGE

16-LEAD PLASTIC SSOP

PGND

GND

CTL

SHDN

BAK

BACKUP

RESET

LOBAT

JMAX

= 125

= 110

C/ W (GN)

JMAX

= 125

= 110

C/ W (S)

ORDER PART

NUMBER

S8 PART MARKING

LTC1558CS8-3.3
LTC1558CS8-5

155833
15585

JMAX

= 125

= 130

C/ W

TOP VIEW

S8 PACKAGE

8-LEAD PLASTIC SO

GND

CTL

BAK

BACKUP

RESET

LTC1558-3.3/LTC1558-5

ELECTRICAL CHARACTERISTICS

BAT

= 1.2V, T

= 0

C to 70

C unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

UVLO(ON)

UVLO Trip Voltage (Note 4)

LTC1558-3.3

2.90

3.00

3.10

LTC1558-5

4.40

4.55

4.70

UVLO(OFF)

UVLO Recovery Trip Voltage (Note 4)

LTC1558-3.3

3.00

3.10

3.20

LTC1558-5

4.55

4.70

4.85

LOBAT

BAT

UVLO Trip Voltage (Note 5)

0.85

0.9

0.95

Backup Battery Charger

CHGF

Battery Charge Current

Fast Recharge

CHGT

Programmable Trickle Charge Current Range

0.05

RECH

Fast Recharge Factor (Note 6)

1.35

1.6

1.85

C/C

TRK

Nominal Trickle Charge Multiplier Factor

CHGT

= 1mA

A/A

CTL(CLAMP)

Trickle Charge Clamp Voltage

CHGT

= 1mA

0.45

0.5

0.55

Pushbutton Reset

CTL

CTL Input Threshold

250

CTL

CTL Input Low Time (Debounce Time)

Reset Timer

HRESET

Pushbutton Duration for Hard Reset

1.10

1.8

3.4

RST

RESET Pulse Width

CTL

Low for < t

HRESET

(Soft Reset)

150

CTL

Low for > t

HRESET

(Hard Reset)

115

185

345

RST1

RESET Output Voltage

= 1V, I

SINK

= 10

200

RST

RESET Output Voltage

= 4.25V, I

SINK

= 1.6mA

0.1

0.4

RESET Output Current

Output Source Current, V

= 3.3V

Output Source Current, V

= 5V

Short-Circuit Current

Output Sink Current, V

= 3.3V

Output Sink Current, V

= 5V

Internal V

Monitor Comparator

PLH

UVLO(ON)

Comparator Propagation

= (9% V

+ 300mV), V

= 300mV

Delay (Rising)

Shutdown Pin (Note 3)

SHDN

SHDN Input Threshold

Logic Low, V

0.8

Logic High, V

SHDN

SHDN Pin Bias Current

= 5V, V

SHDN

= 0V

Feedback Pin

FB Pin Bias Current

The

denotes specifications which apply over the full operating

temperature range.

Note 1: Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.

Note 2: Quiescent current is measured during pushbutton reset.

Note 3: Only applies to 16-pin version.

Note 4: Thresholds will track each other and are guaranteed not to overlap.

Note 5: Low cell voltage reset is only triggered when 0.25V < V

CTL

< 0.9V

for at least 20

s while in backup mode.

Note 6: Fast recharge factor is defined as the ratio of charge replenished to
the NiCd battery during fast recharge to the charge drawn from the NiCd
battery during backup.

Note 7: The LTC1558 switches automatically between the low and high
operating current levels. See Applications Information for more details.

LTC1558-3.3/LTC1558-5

TYPICAL PERFOR

CE CHARACTERISTICS

NiCd TERMINAL VOLTAGE (V)

1.0

OUTPUT POWER (mW)

100

125

150

1.1

1.2

1.3

1.4

1558 G01

= 5V (LTC1558-5)

BAK

= 6V

Output Power vs Battery Voltage

OUTPUT VOLTAGE, V

BAK

(V)

SWITCHING FREQUENCY (kHz)

1558 G03

125

100

BATT

= 1.2V

= 3.3V (LTC1558-3.3)

= 330mA

Boost Converter Switching
Frequency

NiCd CELL CAPACITY (mAHr)

BACKUP TIME (HOURS)

0.5

1.0

1.5

2.0

2.5

3.0

125

250

375

500

1558 G02

BATT

= 1.2V

BAK

= 6V

OUT

= 100mW

Backup Time vs Battery Capacity

Normalized Fast Recharge
Current vs Temperature

Trickle Charge Multiplier Factor

Boost Converter Switching
Duty Cycle

OUTPUT VOLTAGE, V

BAK

(V)

DUTY CYCLE (%)

1558 G04

100

BATT

= 1.2V

= 3.3V (LTC1558-3.3)

= 330mA

NiCd BATTERY TRICKLE CURRENT (mA)

0.05

7.5

TRICKLE CHARGE FACTOR (mA

/mA)

9.5

10.0

10.5

0.1

1558 G05

9.0

8.5

8.0

BATT

= 1.2V

TEMPERATURE (

0.950

CURRENT RATIO (mA/mA)

0.960

0.970

0.980

0.990

1558 G06

1.000

0.955

0.965

0.975

0.985

0.995

1.005

Fast Recharge Time (Assume
Fully Exhausted NiCd Battery)

BATTERY CAPACITY (mAHr)

TIME (HOURS)

128

256

1558 G07

512

RESET Output Voltage
vs Supply Voltage

SUPPLY VOLTAGE (V)

RESET VOLTAGE (V)

4.55V

1558 G08

4.7V

= 5V (LTC1558-5)

RESET Output Voltage
vs Supply Voltage

SUPPLY VOLTAGE (V)

RESET VOLTAGE (V)

0.5

1.0

1.5

2.0

3.5

1558 G09

2.5

3.0

3.10V

= 3.3V (LTC1558-3.3)

LTC1558-3.3/LTC1558-5

CTIO

Pin Numbers are Shown First for the SO-8 Package
Then the GN16 and S16 Packages

SW (Pins 1/1, 2): Boost Converter Switching Node. Con-
nect a 22

H inductor from SW to the positive terminal of

the backup cell. In backup mode, this node is alternately
switched between ground and V

BAK

, generating the backup

output voltage. In fast or trickle charge mode, an internal
regulator outputs a constant DC current from this pin
through the 22

H inductor and into the NiCd battery.

During power-up or undervoltage lockout (UVLO), the SW
pin enters a high impedance state.

GND (Pins 2/4): System Ground. The low power internal
circuitry returns to this pin in the 16-pin packages. GND
and PGND are bonded together to this pin in the SO-8.

CTL (Pins 3/5): Control. This pin provides three functions.
In backup mode this pin enters a high impedance state and
monitors the backup battery cell voltage (V

BAT

). If V

BAT

drops below 0.9V, the LTC1558 enters into UVLO. During
trickle charge mode, an external resistor R

EXT

sets the

trickle charge current. In all modes, pulling the CTL pin
below 250mV will generate either a "soft" or "hard" reset
pulse. See the Applications Information section for more
information.

FB (Pins 4/7): Output Voltage Feedback. This pin is fed to
the LTC1558's internal comparators. The boost converter's
output voltage is set with an external resistor divider
connected from V

BAK

to FB. The LTC1558 enters backup

mode when FB drops 7.5% below the internal reference
voltage (V

REF

). During backup, the boost converter runs

whenever FB drops below this (V

REF

7.5%) threshold.

The LTC1558 exits backup mode when FB rises above
(V

REF

6%).

RESET (Pins 5/11): System Reset, Active Low. This is an
open-drain output. This pin provides a low going reset
signal to the system processor. A 200ms pulse is gener-
ated if the CTL pin is pulled low for more than two seconds
("hard" reset) or when the LTC1558 comes out of UVLO.
The "hard reset" stops the internal boost converter if it is
running. This pin is held low whenever the LTC1558 is in
UVLO and is guaranteed to be valid when V

is greater

than or equal to 1V.

RESET also provides a low going 100

s signal if the CTL

pin is pulled low for less than two seconds ("soft" reset).
Unlike hard reset, soft reset does not affect the LTC1558's
current operating mode.

BACKUP (Pins 6/13): Backup Active. This is an open-drain
output that pulls low unless the LTC1558 is in backup
mode. BACKUP signals the system controller that the
system is in backup mode so that it can reduce system
loading. BACKUP can also be used to drive the gate of a
P-channel MOSFET in series with the main system
regulator's input. A 12V Zener diode is connected inter-
nally to this pin to act as a voltage clamp. See the
Applications Information section for more details.

(Pins 7/14): Power Supply Input. All internal circuits

except the boost converter are powered from this pin. A
0.1

F bypass capacitor is required from V

to ground.

The UVLO detector inside the LTC1558 monitors V

.If

drops below the rated output voltage by greater than

9%, the LTC1558 enters UVLO mode and RESET is as-
serted. The LTC1558 will only exit from UVLO if V

rises

to greater than 6% of the rated output voltage. See the
Applications Information section for more details.

BAK

(Pins 8/15, 16): Backup Supply Output. The LTC1558's

boost converter provides regulated output voltage to the
system through V

BAK

during backup mode.

16-Pin GN and SO Package

PGND (Pin 3): Power Ground. The internal driver circuitry
returns to this pin. PGND should be connected to a low
impedance ground plane in close proximity to the NiCd
battery cell.

SHDN (Pin 6): Chip Shutdown. A TTL-compatible active
low voltage at SHDN puts the LTC1558 into low power
shutdown mode. In shutdown, all internal circuits power
down and are held in a reset state. The SW, CTL and V

BAK

pins enter into high impedance states. In shutdown mode,
supply current drops to below 50

A and current drawn

from the backup cell drops to below 15

LTC1558-3.3/LTC1558-5

CTIO

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.

BAT

BACKUP

RESET

BAK

1558 SW02

200ms

RATED BATTERY TERMINAL VOLTAGE

RATED V

VOLTAGE

SWITCHI

G WAVEFOR

LEVEL SENSE

AND DEBOUNCE

THERMAL

LIMIT

SHUTDOWN

LOGIC

BANDGAP

REF

= 1.272V

CHARGER

RESET

GENERATOR

BOOST/BACKUP

LOGIC

GAS GAUGE

REF

SHDN

RESET

BAK

CTL

UVLO

DETECTOR

RESET

BACKUP

LOBAT

1558 BD

BLOCK DIAGRA

1558 SW01

BAT

MAIN
BATTERY

MULTIPLE
POWER
OUTPUTS

1.2V
NiCd

LTC1558

RESET

BAK

EXT

BACKUP

TO
SYSTEM
CONTROL

FOR MORE DETAILED APPLICATION SCHEMATICS
PLEASE REFER TO THE TYPICAL APPLICATIONS SECTION

MAIN SYSTEM

REGULATOR

Simplified LTC1558 Connections in a

Battery Backup System

Cold Power Boot-Up (Main Battery Replaced/Turned On)

LTC1558-3.3/LTC1558-5

SWITCHI

G WAVEFOR

Cold Power Boot-Up Description

1. The V

BAT

voltage increases and turns on the Q

EXT

body

diode. V

BAK

follows V

BAT

by one body diode drop.

2. V

BAK

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 V

= 1V.

3. The LTC1558's internal bandgap wakes up. The

LTC1558's internal boost converter does not turn on as
RESET remains asserted. Once V

is greater than

REF

6%), BACKUP is deasserted after the t

PHL

delay

time. Q

EXT

turns on and V

BAK

= V

BAT

4. RESET is asserted for a further 200ms after V

exceeds 6% of its rated value.

Backup Mode Description

1. Trigger into Backup Mode. The main battery fails and

drops 7.5% below the LTC1558's internal V

REF

. The

BACKUP pin is asserted after a t

RISE

delay time and the

LTC1558's boost converter is turned on.

2. Backup Mode. The LTC1558's boost converter charges

and discharges the inductor with 165mA peak current.
If V

doesn't recover above (V

REF

7.5%) (due to a

heavy load), the boost converter increases peak charg-
ing current to 330mA. When V

rises above

REF

7.5%), the boost converter stops but the

BACKUP pin remains asserted.

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 V

is pulled higher than (V

REF

6%). BACKUP

deasserts and the boost converter finishes its last cycle.

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.

Backup Mode (Main Battery Discharged)

INDUCTOR

CURRENT

RESET

BACKUP

NICD

LOBAT

1558 SW03

RISE

7.5%

1.2V

7.5%

0.9V

BOOST CONVERTER OUTPUT

FALL

RISE

LTC1558-3.3/LTC1558-5

APPLICATIO

S I

FOR

ATIO

Overview

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
design flexibility. The LTC1558 allows the use of a low cost
rechargeable NiCd cell for backup, eliminating the need for
expensive, replaceable 4.5V lithium backup cells.

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.

Included in the LTC1558 is a complete backup circuit that
monitors the main system power and automatically
switches in the backup circuit as the primary power supply
falls away (due to a weak or disconnected main battery).
The LTC1558 also performs V

supervisory functions

during normal system operations. An LTC1558-3.3 moni-
tors a 3.3V supply voltage at its V

pin whereas an

LTC1558-5 monitors a 5V supply at its V

pin. In both

cases, the LTC1558 derives power for the majority of the
internal circuitry (except for the boost converter) from the
V

pin. Table 1 shows the signal conditions for the

LTC1558's various operating modes. Note that V

Table 1 refers to the rated V

voltage, 3.3V or 5V.

Boost Converter Operation

The LTC1558 uses an onboard synchronous boost con-
verter 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 by the external divider connected
to the FB pin, supports the main system regulator during

Figure 1. Typical LTC1558 Connection

BOOST

CONVERTER

TO SYSTEM REGULATOR INPUT

LTC1588

MAIN
BATTERY

1558 F01

BACKUP

LOGIC

REF

BAK

BACKUP

backup. It can supply a minimum backup power of
100mW. The boost converter operates in a modified pulse
skipping mode; each switch cycle transfers a known
amount of charge from the backup cell to the regulated
output. This prevents uncontrolled discharge of the backup
cell and allows the LTC1558 to accurately measure the
charge removed from the backup cell by counting the
charge pulses.

The LTC1558 enters backup mode when the main battery
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 V

REF

(1.272V), switching the LTC1558 into backup mode
when V

drops 7.5% below V

REF

. Upon entering backup

mode, the BACKUP pin is asserted and the internal boost
converter turns on. The BACKUP signal is used to turn off
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 C

of the system regulator until V

rises

above (V

REF

7.5%).

Table 1

OPERATING MODES

CONDITIONS

UVLO Reset

1V < V

< V

(Rated Value) 9%

or V

BAT

< 0.9V

Pushbutton Reset

CTL

< 250mV

UVLO Reset Recovery

> V

(Rated Value) 6%

Backup Mode Activation

< (V

REF

7.5%)

Backup Mode Exit

> (V

REF

6%)

Boost Converter Activation

< (V

REF

7.5%)

Boost Converter Deactivation

> (V

REF

7.5%)

LTC1558-3.3/LTC1558-5

Once V

rises above (V

REF

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
drained away and V

again drops below (V

REF

7.5%).

The BACKUP pin remains asserted until the main battery
is restored. This ensures that the LTC1558 does not switch
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

falls below (V

REF

7.5%), the boost operation starts

by connecting the SW pin to ground through an internal
0.5

N-channel MOSFET (N1 in the Block Diagram). The

current through the external 22

H inductor rises linearly

through this switch.

LIGHT CURRENT MODE

165mA
(PEAK)

330mA
(PEAK)

HEAVY CURRENT MODE

1558 F02

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
V

BAK

pin through an internal 2

P-channel MOSFET (P1 in

the Block Diagram). The inductor current discharges
through P1, charging up the capacitor connected exter-
nally to V

BAK

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 V

BAK

. 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 V

has increased above the (V

REF

7.5%) threshold,

the boost converter shuts off both switches and waits for
V

to drop below (V

REF

7.5%) again.

If V

is still less than (V

REF

7.5%) after the first boost

cycle, the LTC1558 immediately reconnects SW to ground,
repeating the boost cycle. If after two consecutive pulses,
V

is still not above the boost threshold (V

REF

7.5%),

the LTC1558 decides that the load is not so light after all,

APPLICATIO

S I

FOR

ATIO

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 · LI

), doubling the available

output power. When V

exceeds the (V

REF

7.5%) boost

threshold, the LTC1558 stops the boost converter and
resets the internal two pulse counter. The next time V

falls below (V

REF

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 V

BAK

will hover around the user pro-

grammed value.

BAK

Capacitor ESR

The type of output capacitor and the user programmed
V

BAK

value will affect the LTC1558's output ripple and

efficiency. In most applications, the main V

BAK

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.

BOOST

CYCLE

BAK

ESR RIPPLE

DISCHARGE

PERIOD

DISCH

CHARGE

PERIOD

1588 F03

Figure 3. V

BAK

Ripple

The maximum ripple on the V

BAK

pin is equal to 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 (22

H) and a known peak current

limit, the booster's discharge time in each boost cycle is

LTC1558-3.3/LTC1558-5

proportional to the difference between V

BAK

(3V to 10V)

and the battery cell voltage, V

BAT

(1.2V).

Assuming ESR = 0.2

, I

IND(PEAK)

= 330mA, V

BAK

= 6V,

RIPPLE(P-P)

= (I

IND(PEAK)

)(R

ESR(CAP)

)

= (330mA)(0.2

)

= 66mV

Since V

BAK

must be scaled down to V

, the external

resistor ratio

= 6V/1.272V

= 4.717

Therefore the noise amplitude seen by the FB compara-
tors is:

= 66mV/4.717

= 14mV

The discharge time period,

DISCH

= (L · I

IND(PEAK)

)/(V

BAK

BAT

)

= (22

H · 330mA)/(6V 1.2V)

= 1.5

For lowest V

BAK

= 3V and maximum I

IND(PEAK)

= 445mA,

RIPPLE(P-P)

= 89mV

RB resistor ratio = 2.358

Noise amplitude = 37.7mV

DISCH

= 5

The internal V

comparators are designed to have a slow

response time to filter away this ripple. The (V

REF

6%)

FB comparator has a 6

s rising edge delay and 2

s falling

edge delay. The (V

REF

7.5%) FB comparator has a

similar 6

s rising time delay but a much longer falling

time delay of 20

s. 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.

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 V

BAK

(and V

) to a

higher voltage. The LTC1558 detects the return of the main

APPLICATIO

S I

FOR

ATIO

battery by watching for V

to exceed (V

REF

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
main battery to bypass its body diode and drive the system
regulator directly.

Since the user can replace the main battery anytime during
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.

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 V

BAK

capacitor (C

) drains away. The system regulator will not

maintain its output regulation and the system V

will

drop. When V

drops below 9% of the rated voltage for

more than 9

s, the LTC1558's V

supervisory circuit

activates UVLO mode, shutting off the boost converter and
asserting the RESET pins. The 9

s delay prevents the

LTC1558 from being fooled by brief transients or noise
spikes on its V

pin. Upon receipt of the reset signals, the

host system should shut down in a orderly manner. The
LTC1558's V

supervisory circuit will remain alive until

is less than 1V to ensure valid reset pin signals.

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 20

s, 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

LTC1558-3.3/LTC1558-5

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
drops drastically below 0.25V will also trigger UVLO, since
the LTC1558 will treat this as a "hard" reset after 2
seconds.

An optional LOBAT output, available in the 16-pin GN or SO
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
NiCd cell voltage drops below 0.25V without triggering the
0.25V < V

BAT

< 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 (14

s).

The boost converter continues switching but delivers
reduced output power, causing V

to drop. The LTC1558

will enter UVLO either when V

drops below

CC(RATED VOLTAGE)

9%) or after the LTC1558 detects

CTL lower than 0.25V for 2 seconds, in which case "hard"
reset occurs.

The discharging time can also get abnormally long if a
serious overload condition occurs during switching. The
timer will shut off the P-channel pass transistor after 10

protecting the boost converter. The LTC1558 will end up
in UVLO as V

drops below (V

CC(RATED VOLTAGE)

9%).

In addition, the LTC1558 is protected for safe area opera-
tion with an internal thermal shutdown circuit. If the device
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

APPLICATIO

S I

FOR

ATIO

The LTC1558's boost converter is designed so that no
current drains from the battery to the load during output
short circuit or V

= 0V conditions. This assures that the

system can be powered down for a long period of time.
This eliminates the risk of finding a nonfunctioning backup
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 22

H 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 V

= 5V, the gas

gauge divider will increment by one count every 7.5

while the boost converter is running. Full count is reached
after approximately 2.2 hours, equivalent to about 512mAhr
of charge.

Upon entering recharge mode (after the main battery is
restored) the LTC1558 connects a 16mA fast recharge
current source from V

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.

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.

b) The backup cell was replaced while the main supply was

disabled.

c) A backup cycle was terminated prematurely by a "hard"

reset or an output overload.

LTC1558-3.3/LTC1558-5

In these cases, the LTC1558 assumes that the backup cell
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
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
backup cell is assumed to be fully charged and subsequent
backup/recharge cycles resume normally.

Although the LTC1558 will not fully recharge backup cells
larger than 128mAhr capacity upon power-up, it can still
be used with such cells. Such a cell will be fully replenished
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 V

BAK

values, the boost converter effi-

ciency improves and allows more backup time from the
same cell compared to a higher V

BAK

value.

Once it reaches full recharge, a cell bigger than 512mAhr
is likely to overrun the gas gauge counter before it runs out
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.

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 comes out
of backup. This ensures that the backup cell is always
replenished with at least a 1mAhr charge every time the
LTC1558 enters backup mode.

APPLICATIO

S I

FOR

ATIO

Battery Backup Cell Trickle Charge

When the gas gauge counter reaches zero, the LTC1558
terminates fast recharge and reduces the recharge current
to the user-programmed trickle current level. The LTC1558
provides a trickle current that the user can program from
50

A 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 (V

BAT

0.5)/R

EXT

. This

current is internally multiplied to feed back ten times the
R

EXT

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 R

EXT

resistor

value. For example, a 47k resistor from V

BAT

to CTL sets

the trickle charge current to approximately 150

EXT

10I

1.2V
NiCd
CELL

CTL

0.5V

1558 F04

LTC1558

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

LTC1558-3.3/LTC1558-5

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 UVLO circuit also trips if the LTC1558's V

supervi-

sory circuit detects that V

drops below 9% of the rated

voltage due to overload or output short-circuit condi-

tions. Once the UVLO circuit trips, the LTC1558 asserts
the RESET pins until the V

voltage drops below 1V. It will

then remain off until V

rises to within (V

6%) of the

rated output voltage. During power-up from UVLO, the
LTC1558 asserts the RESET pins until the (V

6%)

threshold. Once V

exceeds (V

6%), the RESET pins

remain asserted for another 200ms ("hard" reset) before
being released to inform the system to start operating.

Reset Operation

The LTC1558 includes an onboard pushbutton reset switch
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

APPLICATIO

S I

FOR

ATIO

the CTL signal. A short (less than 2s) low going signal at
CTL will generate a "soft" reset (100

s) pulse at the RESET

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
20ms to prevent multiple resets, allowing the CTL pin to be
connected directly to a pushbutton to ground.

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
and places the CTL, V

BAK

and SW pins into high impedance

states. The SHDN pin has an internal pull-up that ensures
the chip will not shut down if the pin is left floating. The
SHDN pin typically draws 8

A when pulled low at V

= 5V.

The chip consumes less than 50

A during shutdown while

is still alive.

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 R

EXT

in this mode.

Inductor Selection

The LTC1558 is designed to operate with a recommended
inductor value of 22

H (

20%) with < 0.2

DC resistance.

Using inductor values higher than 22

H 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 22

H 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

20ms

DEBOUNCE

> 0.25V

CTL

< 20ms

20ms < t

CTL

< 2s

> 0.25V

"SOFT" PUSHBUTTON RESET AT CTL
A. CTL < 0.25V FOR LESS THAN 20ms
B. CTL > 0.25V FOR MORE THAN 20ms

"HARD" PUSHBUTTON RESET AT CTL
CTL < 0.25V FOR MORE THAN 2s

20ms DEBOUNCE AT FALLING AND RISING RESET EDGE

100

CTL

1558 F05

RESET

CTL

RESET

200ms

CTL

> 2s

20ms

Figure 5. Pushbutton Resets

LTC1558-3.3/LTC1558-5

Table 2. Recommended Inductors

PART

TYP INDUCTOR

MANUFACTURER

NUMBER

VALUE

DCR (

)

Sumida

CD54-220

20%

0.18

Sumida

CDRH73/74

20%

0.2/0.11

Capacitor Selection

The LTC1558 requires a minimum V

BAK

capacitor of 44

to ensure that the boost converter can regulate the output
at 20mA load. The capacitor's ESR should be small (< 0.2

)

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
system regulator. Thus its ratings like V

MAX

, I

RIPPLE(RMS)

etc., will all have to meet the system regulator's specifica-
tions as well.

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
cylindrical cells, reducing system costs and board space.
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
recommended manufacturers and part numbers are listed
in Table 3.

APPLICATIO

S I

FOR

ATIO

Table 3. Button/Cylindrical NiCd 1.2V Cells

PART

CAPACITY

MANUFACTURER

NUMBER

(mAhr)

SERIES

(

)

SAFT

GB60

1.1

(Memory Backup)

GB170

170

0.4

GB280

280

0.4

SAFT

VB10E

100

0.038

(Standard)

VB22E

220

0.022

VB30E

300

0.017

VB60E

600

0.014

Sanyo

N-50AAA

0.055

(Standard)

N-110AA

120

0.03

N-120TA

130

0.034

N-150N

170

0.027

N-200AAA

220

0.021

N-270AA

305

0.015

N-500A

500

0.09

Panasonic

P-11AA

110

0.08

(Standard)

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
due to a larger R/L time constant, decreasing the switching
frequency. It is advisable, especially for batteries with high
internal resistance, to include a 47

F bypass capacitor

across the battery to ensure that the boost converter can
deliver the maximum output power regardless of the NiCd
internal resistance.

LTC1558-3.3/LTC1558-5

TYPICAL APPLICATIO

LTC1558-3.3 Low Main Battery Voltage (4.5V to 10V) Application

SENSE

INTV

BOOST

OSC

SGND

PGND

RUN/SS

OSENSE

LTC1435

0.1

SENSE

0.033

L1*

C3
4.7

16V

D1 CMDSH-3

1558 TA03

D2
MBRS140T3

R5
20k
1%

SUMIDA CDRH125-10
IRC LR2D1D-01-RQ33-F
SUMIDA CD54-220

35.7k

C5
1000pF

Q2
N-CHANNEL
Si4412DY

Q1
N-CHANNEL
Si4412DY

SFB

EXTV

C2
1

100pF

OSC

68pF

10k

0.1

330pF

C1
100pF

51pF

35V

100

10V

OUT

3.3V
3A

CTL

C11
47

6.3V

BACKUP
BATTERY
1.2V
NiCd

MAIN

BATTERY

4.5V TO 10V

Q11

P-CHANNEL

Si4431DY

R14
14k

LTC1558-3.3

L11

GND

R11
221k
1%

R12
100k
1%

RESET

PUSHBUTTON

BAK

RESET

BACKUP

R13
100k

C12
1

RESET

BACKUP

Typical "Low Voltage" Application

The maximum main battery voltage is less than the maxi-
mum V

BAK

pin voltage (12V). This configuration has the

lowest number of external components.

The LTC1435's minimum input voltage is 3.5V. The V

BAK

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

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.

A 100k pull-up resistor enables the open-drain BACKUP
pin to turn the external P-channel MOSFET off when V

BAK

is higher than V

LTC1558-3.3/LTC1558-5

TYPICAL APPLICATIO

LTC1558-5 Medium Main Battery Voltage (7V to 18V) Application

SENSE

INTV

BOOST

OSC

SGND

PGND

RUN/SS

OSENSE

LTC1435

0.1

SENSE

0.033

L1*

C3
4.7

16V

D1 CMDSH-3

1558 TA04

D2
MBRS140T3

R6
11k
1%

SUMIDA CDRH125-10
IRC LR2D1D-01-RQ33-F
SUMIDA CD54-220

35.7k

C5
1000pF

Q2
N-CHANNEL
Si4412DY

Q1
N-CHANNEL
Si4412DY

SFB

EXTV

C2
1

100pF

OSC

68pF

10k

0.1

330pF

C1
100pF

51pF

35V

OUT

100

10V

OUT

5V
3A

CTL

C11
47

6.3V

BACKUP
BATTERY
1.2V
NiCd

MAIN

BATTERY

7V TO 18V

Q11

P-CHANNEL

Si4431DY

R14
14k

LTC1558-5

L11

GND

R11
422k
1%

R12
100k
1%

RESET

PUSHBUTTON

BAK

RESET

BACKUP

R13
100k

C12
1

D11
1N5818

RESET

BACKUP

Typical "Medium Voltage" Application

The maximum main battery voltage is more than the
maximum V

BAK

pin voltage (12V). This configuration is

needed for most notebook computers that have 3-cell or
4-cell series connected lithium battery packs.

The Schottky diode D11 (1N5818) prevents the main
battery's high terminal voltage from overstressing the
LTC1558's V

BAK

pin during nonbackup conditions. An

internal Zener inside the LTC1558 will clamp V

BAK

to 12V

when the 1N5818's reverse bias leakage current
increases at high temperature.

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 V

BAK

is higher than V

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.

LTC1558-3.3/LTC1558-5

TYPICAL APPLICATIO

LTC1558-5 High Main Battery Voltage (48V) Application

PGATE

P-DRIVE

SENSE

CAP

SHUTDOWN 2

RGND

NGATE

PGND

SGND

SHUTDOWN 1

SENSE

LTC1149-5

C2
0.068

C1
0.047

D1
1N4148

R11
422k
1%

R12
100k
1%

R16

100k

Z11
12V

Q12

2N3906

1N4148

3300pF

R15
100k

MAIN
BATTERY
48V

Q11

P-CHANNEL

MTD2955E

C4
470pF

C3
3.3

C5
1000pF

Q2
N-CHANNEL
IRFZ34

D3
MBR380

C6
0.1

L1*

SENSE

0.04

OUT

220

10V
OS-CON

1558 TA05

OUT

5V
2.5A

*HURRICANE LAB HL-KI168M
**IRC LR2512-01-RO40-5

SUMIDA CD54-220

Q1
P-CHANNEL
MTD2955E

SHUTDOWN

100

100V

CTL

C11
47

6.3V

BACKUP
BATTERY
1.2V
NiCd

R14
14k

LTC1558-5

L11

RESET
PUSHBUTTON

D11
MBR170

BAK

RESET

BACKUP

GND

C12
1

RESET

BACKUP

Typical "High Voltage" Application

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 V

BAK

pin during nonbackup conditions. An

internal Zener inside the LTC1558 will clamp V

BAK

to 12V

when the MBR170's reverse bias leakage current
increases at high temperature.

As shown above, the design must ensure that V

BAT

does

not force the external P-channel MOSFET's V

above its

maximum rating (15V for the MTD2955E) shown during
nonbackup mode.

During nonbackup mode, the LTC1558's open-drain
BACKUP pin is low. The external 12V Zener and 2N3906
conduct and the MTD2955E's V

is clamped at approxi-

mately 12V. During backup, the BACKUP pin floats and the
2N3906's base voltage is pushed nearer to V

BAK

. The

MTD2955E is effectively turned off, isolating the main
battery from V

BAK

during backup.

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.

LTC1558-3.3/LTC1558-5

PACKAGE DESCRIPTIO

Dimensions in inches (millimeters) unless otherwise noted.

0.016 0.050
0.406 1.270

0.010 0.020

(0.254 0.508)

TYP

0.008 0.010

(0.203 0.254)

0.150 0.157**

(3.810 3.988)

0.386 0.394*

(9.804 10.008)

0.228 0.244

(5.791 6.197)

S16 0695

0.053 0.069

(1.346 1.752)

0.014 0.019

(0.355 0.483)

0.004 0.010

(0.101 0.254)

0.050

(1.270)

TYP

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

S8 Package

8-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

0.150 0.157**

(3.810 3.988)

0.189 0.197*

(4.801 5.004)

0.228 0.244

(5.791 6.197)

0.016 0.050
0.406 1.270

0.010 0.020

(0.254 0.508)

TYP

0.008 0.010

(0.203 0.254)

SO8 0996

0.053 0.069

(1.346 1.752)

0.014 0.019

(0.355 0.483)

0.004 0.010

(0.101 0.254)

0.050

(1.270)

TYP

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

S Package

16-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

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-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

LTC1558-3.3/LTC1558-5

1558f LT/TP 0298 4K · PRINTED IN USA

LINEAR TECHNOLOGY CORPORATION 1998

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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Complete Power Management Controller for Battery
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Burst Mode and PowerPath are trademarks of Linear Technology Corporation.

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LTC1558CS-5

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LTC1558CS-5