LTC1559-3.3/LTC1559-5

Backup Battery Controller

with Fixed Output

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

Generates Fixed Backup Voltage (3.07V/4.63V) from
a Single 1.2V NiCd Button Cell

Automatic Main Supply to Backup Switching

Minimum 100mW Output Power

Automatic Fast Recharge of NiCd Battery

Programmable NiCd Trickle Charge Current

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

Onboard Power-Up and Push-Button Reset
Generator

Performs V

Supervisory Functions

Reset Assertion Guaranteed at V

= 1V

Short-Circuit Protection

Thermal Limiting

FEATURES

DESCRIPTIO

The LTC

1559 is a backup battery controller that provides

all the functions necessary to implement a backup 3.3V or
5V power supply using a single NiCd cell. It includes a 1.2V
to 3.07V/4.63V boost converter, an intelligent 2-stage
battery charger, automatic backup switching and a micro-
processor reset generator. The boost converter uses a
synchronous switching architecture to achieve a typical
efficiency of 70%, ensuring maximum backup lifetime
from a small NiCd cell.

The on-chip NiCd charger uses an internal gas gauge to
minimize fast recharge time and prevent overcharging of
the backup cell, thereby improving system efficiency and
extending the life of the backup cell. The LTC1559 also
provides a user programmable trickle charge current to
compensate for self-discharge losses in the backup cell.

The LTC1559's automatic backup switching scheme
requires minimum intervention from the host system and
provides feedback to the host to minimize system loading
in the backup state. Its internal V

fault detector and reset

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

The LTC1559 is available in an SO-8, 16-pin GN or SO
package.

APPLICATIO

Notebook Computers

Palmtop Computers/PDAs

Portable Instruments

Battery-Powered Systems

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

TYPICAL APPLICATIO

CTL

C1
1

**BACKUP

BATTERY

1.2V

NiCd

MAIN

BATTERY

4.5V TO 28V

R1
68k

LTC1559-3.3

*L1

GND

RESET

1559 TA01

BAK

RESET

BACKUP

100

10V

OUT

3.3V AT NORMAL MODE
3A

BAK

33mA (3.07V) AT BACKUP MODE

>33mA (3.3V) AT NORMAL MODE

C2
1

SYSTEM

R2
100k

P-MOSFET

Si9424DY

* SUMIDA CD54-22

** PANASONIC P-11AAH
CONSULT LTC1435 DATA SHEET FOR
APPLICATION CIRCUIT INFORMATION

LTC1435

SYNCHRONOUS

BUCK

REGULATOR

Backup Time vs

BAK

Output Load Current

BAK

LOAD CURRENT (mA)

BACKUP TIME (MINUTES)

800

700

600

500

400

300

200

100

1559 TA02

BAK

= 3.07V

NiCd CELL = P-11AAH
(110mA Hrs)

LTC1559-3.3/LTC1559-5

ABSOLUTE

AXI

RATINGS

(Note 1)

Terminal Voltages

........................................................................ 6V

BAK

.................................................................... 12V

SW ...................................................................... 14V
All Other Pins .............................. 0.3V to V

+ 0.3V

SW Input Currents ............................................. 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

ORDER PART

NUMBER

ORDER PART

NUMBER

S8 PART MARKING

LTC1559CS8-3.3
LTC1559CS8-5

ELECTRICAL CHARACTERISTICS

BAT

= 1.2V, T

= 0

C to 70

C unless otherwise noted.

LTC1559CGN-3.3
LTC1559CGN-5
LTC1559CS-3.3
LTC1559CS-5

Consult factory for Industrial and Military grade parts.

JMAX

= 125

= 130

C/ W

TOP VIEW

S8 PACKAGE

8-LEAD PLASTIC SO

GND

CTL

BAK

BACKUP

RESET

JMAX

= 125

= 110

C/ W (GN)

JMAX

= 125

= 110

C/ W (S)

TOP VIEW

S PACKAGE

16-LEAD PLASTIC SO

GN PACKAGE

16-LEAD PLASTIC SSOP

PGND

GND

CTL

SHDN

BAK

BACKUP

RESET

LOBAT

PACKAGE/ORDER I

FOR

ATIO

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Battery Backup Switching

Operating Voltage Range

LTC1559-3.3

2.900

3.5

LTC1559-5

4.400

5.5

BAT

Backup Battery Cell Voltage

1.0

1.2

1.5

VCC

Quiescent Supply Current (Note 2)

155

250

BAT

Peak Inductor Current (Backup)

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/Booster Assertion

LTC1559-3.3

3.011

3.070

3.127

Trip Point (Note 4)

LTC1559-5

4.475

4.625

4.775

BAK(OFF)

Backup Deassertion Trip Point

LTC1559-3.3

3.061

3.119

3.176

(Note 4)

LTC1559-5

4.550

4.700

4.850

LOBAT1

Low V

BAT

Detect (Note 3)

0.95

1.00

1.05

UVLO(ON)

UVLO Trip Voltage (Note 4)

LTC1559-3.3

2.904

3.003

3.102

LTC1559-5

4.400

4.550

4.700

UVLO(OFF)

UVLO Trip Voltage (Note 4)

LTC1559-3.3

3.061

3.119

3.176

LTC1559-5

4.550

4.700

4.850

155933
15595

LTC1559-3.3/LTC1559-5

ELECTRICAL CHARACTERISTICS

BAT

= 1.2V, T

= 0

C to 70

C unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

UVLO Reset Monitor

LOBAT2

BAT

UVLO Trip Voltage (Note 5)

0.85

0.9

0.95

Backup Battery Charger

CHGF

Battery Charge Current During Fast Recharge

CHGT

User-Programmable Trickle Charge

0.05

Current Range

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)

CTL Clamp Voltage in Trickle Mode

CHGT

= 1mA

0.45

0.5

0.55

Push-Button Reset

CTL

CTL Input Threshold

250

CTL

CTL Input Low Time (Debounce Time)

Reset Timer

HRESET

Push-Button Duration for Hard Reset

1.10

1.8

3.4

sec

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

PS Comparator

HYST

Comparator Threshold Hysteresis

= 25

Internal V

Monitor Comparator

UVLO, Comparator Propagation Delay (Rising)

7.5

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

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 push-button reset.

Note 3: Only applies to 16-pin version.

Note 4: Although the V

BAK(ON)

, V

BAK(OFF)

, V

UVLO(ON)

and V

UVLO(OFF)

threshold voltages have a specification tolerance, they are guaranteed by
design and tested in production never to overlap.

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

CTL

< 0.9V

for at least 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 withdrawn from the
NiCd battery during backup.

Note 7: The LTC1559 switches automatically between the low and high
operating current levels. See Applications Information for more details.

LTC1559-3.3/LTC1559-5

TYPICAL PERFOR

CE CHARACTERISTICS

NiCd TERMINAL VOLTAGE (V)

1.0

OUTPUT POWER (mW)

140

120

100

1.1

1.2

1.3

1.4

1559 G01

= 330mA

= 200

Output Power vs Battery Voltage

Boost Converter Switching
Frequency

Backup Time vs Battery Capacity

Normalized Fast Recharge
Current vs Temperature

Trickle Charge Multiplier Factor

Boost Converter Switching
Duty Cycle

TEMPERATURE (

0.950

CURRENT RATIO (mA/mA)

0.960

0.970

0.980

0.990

1559 G06

1.000

0.955

0.965

0.975

0.985

0.995

1.005

Fast Recharge Time (Assume
NiCd Battery Fully Exhausted)

BATTERY CAPACITY (mA Hr)

TIME (HOURS)

128

256

1559 G07

512

RESET Output Voltage
vs Supply Voltage

SUPPLY VOLTAGE (V)

RESET VOLTAGE (V)

4.55V

1559 G08

4.7V

LTC1559-5

RESET Output Voltage
vs Supply Voltage

OUTPUT VOLTAGE, V

BAK

(V)

DUTY CYCLE (%)

1559 G04

100

LTC1559-3.3
V

BAT

= 1.2V

= 330mA

NiCd CELL CAPACITY (mA Hr)

BACKUP TIME (HOURS)

3.5

3.0

2.5

2.0

1.5

1.0

0.5

125

250

375

500

1559 G02

BAT

= 1.2V

OUT

= 100mW

OUTPUT VOLTAGE, V

BAK

(V)

SWITCHING FREQUENCY (kHz)

1559 G03

125

100

LTC1559-3.3
V

BAT

= 1.2V

= 330mA

NiCd BATTERY TRICKLE CURRENT (mA)

10.5

10.4

10.3

10.2

10.1

10.0

9.9

9.8

9.7

9.6

9.5

TRICKLE CHARGE FACTOR (mA/mA)

1559 G05

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

SUPPLY VOLTAGE (V)

RESET VOLTAGE (V)

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

1559 G09

LTC1559-3.3

3.12V

LTC1559-3.3/LTC1559-5

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 8-pin
package.

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

BAT

). If V

BAT

drops below 0.9V, the LTC1559 enters UVLO. During
trickle charge mode, an external resistor R

EXT

sets the

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

PS (Pins 4/7): Power Supply Sense. This pin senses the
presence of the main supply and triggers the LTC1559 to
terminate backup mode. During backup, V

is driven

externally by the LTC1559's boost convert's output (V

BAK

When PS > V

during backup, the LTC1559 pulls down

the BACKUP pin, reconnecting the system regulator out-
put to the system V

. The PS pin is needed in applications

that use a P-channel MOSFET (driven by the BACKUP
signal) to isolate the system regulator during backup. If
not needed, PS can be disabled by tying it to ground.

RESET (Pins 5/11): System Reset, Active Low. This is an
open-drain output. This pin provides a low going reset
signal to the system processor. A 200ms pulse is gener-
ated if the CTL pin is pulled low for more than two seconds
("hard" reset) or if the LTC1559 comes out of UVLO. This
"hard reset" stops the internal boost converter if it is
running. This pin is held low if the LTC1559 is in UVLO and

is guaranteed to be valid when V

is greater than or equal

to 1V.

RESET also provides a low going 100

s signal whenever

the CTL pin is pulled low for less than two seconds ("soft"
reset). Unlike hard reset, soft reset does not affect the
LTC1559's current operating mode.

BACKUP (Pins 6/13): System Backup Signal. This is a
TTL-compatible output driver that pulls low unless the
LTC1559 is in backup mode. BACKUP signals the system
controller that the system is in backup mode so that it can
reduce system loading. BACKUP can also be used to drive
the gate of a P-channel MOSFET in series with the main
system regulator's output. See the Applications Informa-
tion section for more details.

(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 LTC1559 monitors V

. If

drops below the rated output voltage by 9%, the

LTC1559 enters UVLO mode and RESET is asserted. The
LTC1559-3.3 exits UVLO if V

rises to greater than

5.5% of the rated output voltage. The LTC1559-5 exits
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 LTC1559's

boost converter provides the regulated output voltage to
the system through V

BAK

during backup mode.

16-Pin GN and SO Packages

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

SHDN (Pin 6): Chip Shutdown. A TTL-compatible active
low voltage at SHDN puts the LTC1559 into low power
shutdown mode. In shutdown, all internal circuits power
down and are held in a reset state. The SW, CTL and V

BAK

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

A and current drawn

from the backup cell drops to below 15

LTC1559-3.3/LTC1559-5

LOBAT (Pin 9): Low Backup Battery Detector Output. This
is an open-drain output with an internal weak pull-up. It is
asserted if the NiCd cell terminal voltage drops below
1.0V. This pin is pulled high if the LTC1559 is in trickle
charge mode.

CTIO

1559 SW01

BAT

MAIN
BATTERY

OUT

BACKUP

SYSTEM
V

1.2V
NiCd

LTC1559

RESET

EXT

BAK

BACKUP

TO
SYSTEM
CONTROL

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

MAIN SYSTEM

REGULATOR

OUT

BAT

BACKUP

RESET

1559 SW02

200ms

RATED BATTERY TERMINAL VOLTAGE

RATED V

VOLTAGE

5.5% (LTC1559-3.3)
6% (LTC1559-5)

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

Simplified LTC1559 Connections in a Battery Backup System

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

1559 BD

BLOCK DIAGRA

RESET (Pin 12): System Reset, Active High. This is a TTL-
compatible output driver. It can connect to systems that
require active high logic. The RESET output will go high if
RESET is pulled low.

LTC1559-3.3/LTC1559-5

SWITCHI

G WAVEFOR

Cold Power Boot-Up Description

1. System regulator starts to ramp up the output (PS)

once the V

BAT

voltage increases beyond the minimum

input value.

2. V

starts to increase once PS is high enough to turn on

EXT

's body diode. RESET is asserted when V

is less

than or equal to 1V.

3. The LTC1559's internal bandgap wakes up. Q

EXT

turns

on and V

= PS. The LTC1559's internal boost con-

verter does not turn on as RESET remains asserted.

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

reaches

5.5% of its rated V

value for the LTC1559-3.3 and

6% of its rated V

value for the LTC1559-5.

Backup Mode (Main Battery Discharged)--
LTC1559-3.3

INDUCTOR

CURRENT

RESET

BACKUP

NiCd

LOBAT

1559 SW03

1.2V

0.9V

5.5%

BOOST CONVERTER OUTPUT

(4)

(3)

(2)

(1)

"1"

Backup Mode Description

1. Trigger into Backup Mode. Main battery fails and V

drops 7% below the rated value. The backup pin is
asserted after a t

delay time and the boost converter is

turned on.

2. Backup Mode. The LTC1559's boost converter charges

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

doesn't increase above V

(rated value) 7%

(due to a heavy load), the boost converter increases
peak charging current to 330mA. If V

rises above

(rated value) 7%, the boost converter stops and

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 system regulator to increase PS above V

When PS > V

or V

> V

(rated value) 5.5%, the

BACKUP pin deasserts and the boost converter finishes
its last cycle.

4. Trigger into UVLO. During backup, the 1.2V NiCd cell is

discharged and its terminal voltage falls. The LOBAT pin
is asserted to give an early warning if the cell voltage
drops below 1V. RESET is asserted when the cell
voltage drops below 0.9V and the LTC1559 enters
UVLO mode.

LTC1559-3.3/LTC1559-5

APPLICATIO

S I

FOR

ATIO

Overview

The LTC1559 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 sys-
tem design flexibility. The LTC1559 allows the use of a
low cost rechargeable NiCd cell for backup, eliminating
the need for expensive, replaceable 4.5V lithium backup
cells.

The LTC1559 includes an onboard boost converter
designed to generate a fixed voltage (3.07V for 3.3V parts
and 4.625V for 5V parts) from a single 1.2V NiCd cell.
When connected to the system DC/DC converter's output,
the LTC1559 enables the system connected to the V

rail

to continue operation when the main power supply fails. A
"smart" recharging circuit uses an accumulating gas
gauge to measure the charge extracted from the backup
battery during a backup cycle. This measured charge is
then replaced in a fast recharge cycle, without wasting
excess power or overcharging the backup cell. An exter-
nally adjustable trickle charge circuit maintains the cell
charge after the fast charge cycle has completed, minimiz-
ing drain from the main battery during standby.

Included in the LTC1559 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 LTC1559 also performs V

supervisory functions

during normal system operations. An LTC1559-3.3
monitors a 3.3V supply voltage at its V

pin while an

LTC1559-5 monitors a 5V supply at its V

pin. In both

cases, the LTC1559 derives power for the majority of the
internal circuitry (except for the boost converter) from its
V

pin. Table 1 shows the signal conditions for the

various operating modes of the LTC1559-3.3. Table 2
shows the signal conditions for the various operating
modes of the LTC1559-5.

Table 1. LTC1559-3.3 Operating Modes

OPERATING MODES

CONDITIONS

UVLO Reset

1V < V

< V

(rated value) 9% or

BAT

< 0.9V

Push-Button Reset

CTL

< 250mV

UVLO Reset Recovery

> V

(rated value) 5.5%

Backup Mode Activation

< V

(rated value) 7%

Backup Mode Exit

> V

(rated value) 5.5%

or PS > V

Boost Converter Activation

< V

(rated value) 7%

Boost Converter Deactivation

> V

(rated value) 7%

Table 2. LTC1559-5 Operating Modes

OPERATING MODES

CONDITIONS

UVLO Reset

1V < V

< V

(rated value) 9%

or V

BAT

< 0.9V

Push-Button Reset

CTL

< 250mV

UVLO Reset Recovery

> V

(rated value) 6%

Backup Mode Activation

< V

(rated value) 7.5%

Backup Mode Exit

> V

(rated value) 6%

or PS > V

Boost Converter Activation

< V

(rated value) 7.5%

Boost Converter Deactivation

> V

(rated value) 7.5%

Boost Converter Operation

The LTC1559 uses an onboard boost converter with a
fixed peak current architecture that provides a simple and
flexible system solution while eliminating the need for
conventional frequency compensation. The boost
converter's output, set to 93% (LTC1559-3.3) or 92.5%
(LTC1559-5) of the rated V

, supports the system V

during backup. It supplies 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 LTC1559 to accurately measure the
charge removed from the backup cell by counting the
charge pulses.

The LTC1559 enters backup mode when the main battery
voltage drops and causes V

, the system regulator's

output, to fall. As shown in Figure 1, V

is scaled down

by an internal resistor divider and fed to the LTC1559's
backup comparators. These compare the scaled voltage

LTC1559-3.3/LTC1559-5

APPLICATIO

S I

FOR

ATIO

ferred for the first two consecutive switch cycles. If V

falls below V

(rated value) 7% (LTC1559-3.3), the

boost operation starts by connecting the SW pin internally
to ground through an internal 0.5

N-channel MOSFET

(N1 in the Block Diagram). The current through the exter-
nal 22

H inductor rises linearly through this switch.

When the switch current reaches an internally preset level
of 165mA, the boost converter connects the SW pin to the
V

BAK

pin through an internal 2

P-channel MOSFET. The

inductor current discharges through the P-channel (P1 in
the Block Diagram) and charges up the system's V

capacitor (C

OUT

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 LTC1559 monitors the V

voltage.

If V

has increased above the V

(rated value) 7%

(LTC1559-3.3) threshold, the boost converter shuts off
both switches and waits for V

to drop below V

(rated

value) 7% (LTC1559-3.3) again.

with an internal trimmed V

REF

(1.272V), switching the

LTC1559 into backup mode if V

drops 7%

(LTC1559-3.3) or 7.5% (LTC1559-5) below its rated
value. Upon entering backup mode, the BACKUP pin is
asserted and the internal boost converter turns on. The
BACKUP signal turns off the external P-channel MOSFET
(if used), isolating the system regulator from the LTC1559.
The boost converter charges the V

capacitor, C

OUT

, of

the system regulator until V

rises above V

(rated

value) 7% (LTC1559-3.3) or V

(rated value) 7.5%

(LTC1559-5).

Once V

rises above V

(rated value) 7% (LTC1559-

3.3), the boost converter deactivates and the freshly
charged V

capacitor C

OUT

supplies power to the system.

The cycle repeats again when the V

capacitor's charge

is drained away and V

again drops below V

(rated

value) 7% (LTC1559-3.3). The BACKUP pin remains
asserted until the main battery is restored. This ensures
that the LTC1559 does not switch in and out of backup
mode unnecessarily.

The LTC1559's boost converter minimizes output ripple
under light load conditions by reducing the charge trans-

Figure 1. Typical LTC1559 Connection

BOOST

CONVERTER

SYSTEM

REGULATOR

LTC1559

1559 F01

BACKUP

LOGIC

REF

BACKUP

SYSTEM
V

BAK

OUT

LIGHT CURRENT MODE

165mA
(PEAK)

330mA
(PEAK)

HEAVY CURRENT MODE

1559 F02

Figure 2. Inductor Current During Switching

Figure 3. V

BAK

Ripple

BOOST

CYCLE

BAK

ESR RIPPLE

DISCHARGE

PERIOD

DISCH

CHARGE

PERIOD

1559 F03

LTC1559-3.3/LTC1559-5

If V

is still less than V

(rated value) 7% (LTC1559-

3.3) after the first boost cycle, the LTC1559 immediately
reconnects SW to ground, repeating the boost cycle. If
after two consecutive pulses, V

is still not above the

boost threshold V

(rated value) 7% (LTC1559-3.3),

the LTC1559 decides that the load is not so light after all,
and doubles the internal inductor charging current limit to
330mA for subsequent cycles. This is high current mode.
By doubling the peak inductor current, each boost cycle
effectively carries four times more energy compared to
low current mode (E = 1/2 · LI

), doubling the available

output power. When V

exceeds the V

(rated value)

7% (LTC1559-3.3) boost threshold, the LTC1559 stops
the boost converter and resets the internal 2-pulse counter.
The next time V

falls below V

(rated value) 7%

(LTC1559-3.3), the boost converter restarts in low current
mode for at least two boost cycles. Moderate or changing
loads cause the LTC1559 to shift between the two peak
inductor current limits, keeping the output in tight regula-
tion. Near its maximum load capability, the LTC1559 will
stay in 330mA high current mode and the output voltage
V

BAK

will hover around V

(rated value) 7%

(LTC1559-3.3).

Capacitor ESR

The type of output capacitor and the rated V

value will

affect the LTC1559's output ripple and efficiency. In most
applications, the V

capacitor is primarily determined by

the requirements of the main power supply. Such a
capacitor will generally meet the requirements of the
LTC1559. In unusual circumstances or circuits where
the main system V

capacitor is located some distance

away from the LTC1559, a local output capacitor may be
necessary.

The ripple on the V

pin is equal to the capacitor ESR

voltage drop due to the boost converter's output current
pulses. The ripple frequency and output duty cycle is
proportional to the inductor discharge time. Given a fixed
inductor value (22

H) and a known peak current limit, the

booster's discharge time in each boost cycle is propor-
tional to the difference between V

BAK

(93% of the rated V

for the LTC1559-3.3 and 92.5% of the rated V

for the

LTC1559-5) and the battery cell voltage, V

BAT

(1.2V).

APPLICATIO

S I

FOR

ATIO

Assuming ESR = 0.2

, I

IND(PEAK)

= 330mA, V

= 5V,

RIPPLE(P-P)

= (I

IND(PEAK)

)(R

ESR(CAP)

)

= (330mA)(0.2

)

= 66mV

Since V

must be scaled down internally, the external

resistor ratio:

= 5V/1.272V

= 3.931

Therefore the ripple seen by the V

comparators is:

= 66mV/3.931

= 16.79mV

The discharge time period,

DISCH

= (L · I

IND(PEAK)

)/(V

BAK

BAT

)

= (22

H · 330mA)/(4.625 1.2V)

= 2.12

For V

= 3.3V and I

IND(PEAK)

= 330mA,

RIPPLE(P-P)

= 66mV

RB resistor ratio = 3.3/1.272 = 2.594

Ripple voltage = 25.4mV

DISCH

= 3.9

The internal V

comparators are designed to have a slow

response time to filter away this ripple. The V

(rated

value) 5.5% (LTC1559-3.3) and V

(rated value) 9%

comparators have a 6

s rising edge delay and 2

s falling

edge delay. The V

(rated value) 7% (LTC1559-3.3)

comparator has a similar 6

s rising time delay but a much

longer falling time delay of 20

s. This enables the com-

parator to control the boost converter properly, and avoids
turning off the boost converter prematurely due to false
triggering by the ESR ripple.

Exit from Backup

When a main battery is inserted into the system, the
LTC1559 follows a specific sequence to exit backup mode
and return control to the main supply. The sequence
depends on the type of main power supply used. In
systems where the main supply's output impedance is

LTC1559-3.3/LTC1559-5

APPLICATIO

S I

FOR

ATIO

to the load while charge on the V

capacitor drains away.

If V

drops below V

(rated voltage) 9% for more than

7.5

s, the LTC1559's V

supervisory circuit activates

UVLO mode, shutting off the boost converter and assert-
ing the Reset pins. The 7.5

s delay prevents the LTC1559

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

pin. Upon receipt of the reset signal, the host system

should shut down in an orderly manner. The LTC1559's
V

supervisory circuit will remain alive until V

is less

than 1V to ensure a valid RESET pin signal.

Backup Cell Voltage Monitoring

As the boost converter removes charge from the backup
NiCd cell, the cell's terminal voltage falls. Permanent
damage to the NiCd cell can occur if it is discharged to
below 0.9V. To prevent this, the LTC1559 monitors the
cell's terminal voltage through the CTL pin during backup.
If the CTL pin drops below 0.9V for more than 20

s, the

UVLO circuit shuts down the boost converter and asserts
the RESET and RESET pins. Since the CTL pin can also be
connected to an external push-button reset, the LTC1559
includes internal logic to ensure that the low cell voltage
reset is triggered only if the CTL pin is between 0.9V and
0.25V. This will prevent a push-button reset (which pulls
CTL below 250mV) from being mistaken as a low cell
voltage condition. Unusual situations where the NiCd cell
voltage drops drastically below 0.25V will also trigger
UVLO, since the LTC1559 will treat this as a "hard" reset
after two seconds.

An optional LOBAT output, available in the 16-pin GN or SO
package, can be used to signal the system if the cell
voltage falls below 1V, giving an early warning that the
backup cell is heavily discharged. The LOBAT pin is
disabled if the LTC1559 is in trickle charge mode,
because the CTL pin is regulated to 0.5V by the LTC1559.

Fault Protection and Thermal Limit

The LTC1559's boost converter incorporates two internal
timers that turn off the switch transistors if the inductor
charge or discharge time gets abnormally long.

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

high when inactive (typically a boost regulator with an
output catch diode), the LTC1559 detects the return of the
main supply by watching for V

to exceed V

(rated

value) 5.5% (LTC1559-3.3). The LTC1559 then shuts
down its internal boost converter and begins to recharge
the NiCd cell. In such applications, the PS pin is not used
and can be tied to ground. No external P-channel MOSFET
is required to isolate the main supply from the system V

during backup.

In systems where the main supply's output impedance is
low when inactive (typically buck regulators), the main
supply must be disconnected from the system V

during

backup to prevent the inactive supply from loading the
LTC1559. This is typically accomplished using an external
P-channel MOSFET as shown in Figure 1. When the main
supply is restored, the P-channel MOSFET's body diode
forward-biases. This allows current to flow into the sys-
tem V

, but the forward drop across this diode may

prevent V

from reaching the V

(rated value)

5.5% (LTC1559-3.3) threshold that deactivates the
LTC1559's backup mode. In such systems, the PS pin
should connect directly to the output of the main system
supply. When the system regulator's voltage rises about
2.5% above the backup V

, the PS comparator triggers

and causes the LTC1559 to deassert the BACKUP pin
signal. This signals the system controller to restore sys-
tem loading and resume normal operation. At the same
time, the external P-MOSFET is driven by the BACKUP
signal. The P-channel MOSFET turns on and allows the
main regulator to bypass its body diode and drive the
system V

directly.

Since the user can replace the main battery anytime during
the LTC1559's backup operation, the BACKUP signal may
be deasserted while the boost converter is switching. To
prevent the potential problem of residual energy in the
inductor, the LTC1559 will only stop the boost converter
after it completes the current boost converter cycle.

UVLO Under Excessive Backup Load

Very heavy loads (above the LTC1559's maximum power
output) will pull the boost converter's output below the
boost threshold. Under these conditions, the LTC1559's
boost converter continues to supply 330mA current pulses

LTC1559-3.3/LTC1559-5

case, the NiCd cell is assumed to be damaged and the
LTC1559's priority is shutting down the system grace-
fully. In this case, the timer will shut off the N-channel
switch transistor after a maximum charging time (14

s).

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

to drop. The LTC1559

enters UVLO if V

drops below V

(rated value)

9% or if the LTC1559 detects that CTL is lower than
0.25V for two seconds, in which case "hard" reset occurs.

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

protecting the boost converter. The LTC1559 enters UVLO
as V

drops below V

(rated value) 9%.

In addition, the LTC1559 has safe area operation protec-
tion with an internal thermal shutdown circuit. If the device
is overloaded for a long period of time, the thermal
shutdown circuit forces the LTC1559 into UVLO. The
threshold temperature for thermal shutdown is typically
155

The LTC1559'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 LTC1559 includes an onboard gas gauge circuit,
consisting of a 23-bit divider and a 9-bit up/down counter.
The gas gauge logic assumes that the boost converter
uses a 22

H inductor, allowing it to accurately measure

battery charge by counting pulses. The gas gauge counts
up from zero as charge is removed from the backup cell in
backup mode. It takes 8.4 million 165mA boost pulses
(low current mode) to increment the up/down counter by
one count. In high current mode, the 330mA pulses skip
the first two bits of the divider because each 330mA pulse
carries four times as much energy as a 165mA pulse. At
maximum load and V

= 4.625V (LTC1559-5), the gas

gauge counter will increment by one count every 7.5

while the boost converter is running. Full count is reached

APPLICATIO

S I

FOR

ATIO

after approximately 2.2 hours, equivalent to about
512mAhr of charge.

Upon entering recharge mode (after the main battery is
restored) the LTC1559 connects a 16mA fast recharge
current source from 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 typically replace 160%
of the charge previously removed from the backup cell.
When the gas gauge counter reaches zero, the LTC1559
reduces the charging current at the SW pin to the user-
programmed trickle charge current level.

Under some circumstances, the LTC1559 can exit backup
mode with invalid gas gauge contents. This occurs under
three possible conditions:

1. The backup cell was completely exhausted during a

backup cycle and the LTC1559 entered UVLO.

2. The backup cell was replaced while the main supply was

disabled.

3. A backup cycle was terminated prematurely by a "hard"

reset or an output overload.

In these cases, the LTC1559 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 into the backup cell (13.9 hours). If the backup
cell is actually exhausted, it will be fully recharged. If the
battery is partially or fully charged, or is significantly
smaller than 128mAhr capacity, the extra charging time is
wasted. However, the LTC1559's 16mA fast charge cur-
rent is not high enough to damage the cell. Once the full-
count recharge has been completed, the backup cell is
assumed to be fully charged and subsequent backup/
recharge cycles resume normally.

Although the LTC1559 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

LTC1559-3.3/LTC1559-5

APPLICATIO

S I

FOR

ATIO

example, a small 60mAhr SAFT cell can back up the
system for 20 minutes at an output power of 100mW. Note
that at V

= 3.07V (LTC1559-3.3), the boost converter

efficiency improves and allows more backup time from the
same cell compared to V

= 4.625V (LTC1559-5).

Once it reaches full recharge, a cell bigger than 512mAhr
will overrun the gas gauge counter before it runs out of
charge during an extended backup cycle. The LTC1559
gas gauge counter will not roll over if this occurs; it will
stay at full count until the backup cycle ends and then
partially recharge the cell with a full count cycle as above.

Very short backup cycles (< 32s) may not extract enough
charge from the backup cell to increment the gas gauge
counter at all. To ensure that the backup cell is not slowly
"nibbled" away, the gas gauge counter is always
incremented by 1mAhr each time the controller exits
backup. This ensures that the backup cell is replenished
with at least a 1mAhr charge every time the LTC1559
enters backup mode.

Battery Backup Cell Trickle Charge

When the gas gauge counter reaches zero, the LTC1559
terminates fast recharge and reduces the recharge current
to the user-programmed trickle current level. The LTC1559
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

Figure 4. Trickle Current Charger

EXT

10I

1.2V
NiCd
CELL

CTL

0.5V

1559 F04

LTC1559

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 LTC1559

trickle charges only after the completion of the fast
recharge cycle, the backup cell voltage should be very
close to 1.2V. This simplifies the calculation of the R

EXT

resistor value. For example, a 47k resistor from V

BAT

CTL sets the trickle charge current to 150

Undervoltage Lockout

The LTC1559 includes an undervoltage lockout (UVLO)
circuit that shuts the system down gracefully if the backup
cell is exhausted or overloaded. As described in the
previous section, the LTC1559 terminates backup opera-
tion and remains off until the main power supply returns.
It then runs a fast recharge cycle to recharge the backup
cell. An onboard low-battery comparator in the 16-pin GN
or SO package provides an early warning signal if the
backup cell drops below 1V.

The UVLO circuit trips if the LTC1559's V

supervisory

circuit detects that V

drops below 9% of the rated V

voltage due to overload or output short-circuit conditions.
Once the UVLO circuit trips, the LTC1559 asserts the
RESET and RESET pins until the V

voltage drops below

1V. It then remains off until V

rises to within 5.5% of

the rated output voltage (LTC1559-3.3). During power-up
from UVLO, the LTC1559 asserts the RESET and RESET
pins until the V

C C

( r a t e d v a l u e) 5.5% (LTC1559-3.3)

threshold. Once V

exceeds V

C C

( r a t e d v a l u e ) 5.5%

(LTC1559-3.3), the RESET and RESET pins remain
asserted for another 200ms ("hard" reset) before being
released to inform the system to start operating.

Reset Operation

The LTC1559 includes an onboard push-button reset
switch controller. If the CTL pin is pulled to ground
(< 250mV) by a push-button or an open-drain output, the
LTC1559 generates a pulse at the RESET and RESET pins
after the trailing edge of the CTL signal. A short (less than
two seconds) low going signal at CTL generates a "soft"
reset (100

s) pulse at the reset pins. A low CTL signal for

more than two seconds generates a "hard" reset pulse at
the RESET and RESET pins. During "hard" reset, the

LTC1559-3.3/LTC1559-5

APPLICATIO

S I

FOR

ATIO

shut off completely. Note that the backup cell slowly
discharges through R

EXT

in this mode.

Inductor Selection

The LTC1559 is designed to operate with a recommended
inductor value of 22

H (

20%) with < 0.2

DC resistance.

Using inductor values above 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 3 lists a few recom-
mended surface mount inductor part numbers.

Table 3. Recommended Inductors

PART

TYP INDUCTOR

DCR

MANUFACTURER

NUMBER

VALUE

(

)

Sumida

CD54-220

20%

0.18

Sumida

CDRH73/74

20%

0.2/0.11

Capacitor Selection

The LTC1559 requires a V

capacitor of 100

F to ensure

that boost converter can regulate the output under maxi-
mum load conditions. The capacitor's ESR should be
small (<0.2

) to minimize voltage spikes that might

incorrectly trigger the LTC1559's internal V

compara-

tors. Note that the LTC1559 can usually share the output
capacitor with the system regulator. However, a 1

F is

recommended directly at the LTC1559's V

pin. The V

capacitor's ratings like V

MAX

, I

RIPPLE(RMS)

all must meet

the system regulator's specifications as well.

Battery Selection

A primary application for the LTC1559 is a "bridging"
supply, only providing backup current while the main
system battery is being replaced. In these applications,
the LTC1559 works well with NiCd button cells or small
cylindrical cells, reducing system costs and board space.
It is optimized for use with up to 512mAhr battery
capacities.

Figure 5. Push-Button Resets

CTL

RESET

(A)

20ms

DEBOUNCE

(B)

> 0.25V

CTL

< 20ms

20ms < t

CTL

< 2s

> 0.25V

"SOFT" PUSH-BUTTON RESET AT CTL
(A) CTL < 0.25V FOR LESS THAN 20ms
(B) CTL > 0.25V FOR MORE THAN 20ms

"HARD" PUSH-BUTTON RESET AT CTL
CTL < 0.25V FOR MORE THAN 2s

20ms DEBOUNCE AT FALLING AND RISING RESET EDGE

100

CTL

1559 F05

RESET

CTL

RESET

200ms

CTL

> 2s

20ms

LTC1559 disables the boost converter if it is in backup
mode. All signals at the CTL pin are debounced for 20ms
to prevent multiple resets, allowing the CTL pin to be
connected directly to a push-button to ground.

The RESET pin is an open-drain output that requires an
external pull-up resistor. The RESET pin is a TTL compat-
ible CMOS output.

Shutdown

The 16-pin LTC1559 has a TTL compatible input, SHDN
that shuts down the whole chip, asserts the RESET and
RESET pins and places the CTL, V

BAK

and SW pins into

high impedance states. The SHDN pin has an internal pull-
up of 8

A that ensures the chip will not shut down if the pin

is left floating. The chip consumes less than 50

A during

shutdown.

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

LTC1559-3.3/LTC1559-5

The LTC1559 works with standard or memory backup
specific NiCd cells. Memory backup cells can operate at
higher temperatures and have lower self-discharge rates.
The LTC1559's trickle charger is designed to accommo-
date both memory backup cells (with low self-discharge)
and standard cells (with higher self-discharge). Some
recommended manufacturers and part numbers are listed
in Table 4.

The internal resistance of the backup cell increases power
dissipation as the boost converter draws current from it
during switching, degrading efficiency. Due to the fixed
inductor peak current architecture, the LTC1559's boost
converter output power drops significantly when the NiCd
cell's internal resistance increases at the end of its charge.
The inductor charging time increases due to a larger R/L
time constant, decreasing the switching frequency. It is
advisable, especially for batteries with high internal resis-
tance, to include a 1

F or larger bypass capacitor across

the battery to ensure that the boost converter can deliver
the maximum output power regardless of the NiCd inter-
nal resistance.

APPLICATIO

S I

FOR

ATIO

Table 4. Button/Cylindrical NiCd 1.2V Cells

MANUFACTURER

PART

CAPACITY

SERIES

(TYPE)

NUMBER

(mAhr)

(

)

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 (Standard)

P-11AA

110

0.08

LTC1559-3.3/LTC1559-5

TYPICAL APPLICATIO

LTC1559-3.3 Backup System with an LTC1435 Main System Regulator (LTC1435 Output Sense at the Drain of Q11)

Description

The PS pin connects to Q11's drain and allows the LTC1559
to detect the restoration of the main battery during backup
mode. Once the LTC1435's output is greater than V

OUT

SENSE

INTV

BOOST

OSC

SGND

PGND

RUN/SS

OSENSE

LTC1435

0.1

SENSE

0.033

L1*

*SUMIDA CDRH125-10
**IRC LR2010-01-R033-F

SUMIDA CD54-220

C3
4.7

16V

CMDSH-3

1559 TA03

D2
MBRS140T3

R5
20k
1%

R1
35.7k
1%

C5
1000pF

100pF

Q2
N-CHANNEL
Si4412DY

Q1
N-CHANNEL
Si4412DY

SFB

EXTV

35V

OSC

68pF

10k

0.1

330pF

C1
100pF

51pF

C2
0.1

BACKUP
OUTPUT
3.3V

MAIN
OUTPUT
3.3V

CTL

C11
1

6.3V

BACKUP
BATTERY
1.2V
NiCd

MAIN
BATTERY
4.5 TO 28V

Q11
P-CHANNEL
Si9424Y

R14
14k

LTC1559-3.3

L11

GND

RESET
PUSH-BUTTON

BAK

RESET

BACKUP

R15
100k

C12
1

RESET

BACKUP

OUT

100

10V

C15
100

10V

during backup mode, the LTC1559 deasserts its BACKUP
pin and returns control back to the LTC1435. Q11 turns on
and allows the LTC1435 to charge C15. Please refer to the
Applications Information section for more details.

LTC1559-3.3/LTC1559-5

PACKAGE DESCRIPTIO

Dimensions in inches (millimeters) unless otherwise noted.

S Package

16-Lead Plastic Small Outline (Narrow 0.150)

(LTC DWG # 05-08-1610)

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

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.

LTC1559-3.3/LTC1559-5

LINEAR TECHNOLOGY CORPORATION 1998

LTC1559-3.3 Backup System with an LTC1435 Main System Regulator

(LTC1435 Output Sense at the Source of Q11, LTC1559's PS Pin Is Grounded)

1559f LT/TP 1098 4K · PRINTED IN USA

PART NUMBER

DESCRIPTION

COMMENTS

LTC690/LTC691

Microprocessor Supervisory Circuits

Microprocessor Power Supply Monitor and Backup with Power Fail

LTC694/LTC695

Comparator

LTC699

Microprocessor Supervisory Circuits

Microprocessor Power Supply Monitor and Backup

LTC1232

Microprocessor Supervisory Circuits

Include Push-Button Reset

LTC1235

Microprocessor Supervisory Circuits

Include Push-Button Reset and Power Fail Comparator

LTC1149

High Efficiency Synchronous Step-Down

up to 48V, Burst Mode

Operation

Switching Regulator

LTC1435

High Efficiency, Low Noise Synchronous

Ultrahigh Efficiency, Burst Mode Operation

Step-Down Switching Regulator

LTC1479

PowerPath

Controller for Dual

Complete Power Management Controller for Battery

Battery Systems

Notebook Computers and Other Portable Equipment

LTC1558

Battery Backup Controller with

Similar to LTC1559 Except That It Backs up the Main System Regulator's

Programmable Output

Input, Allowing Backup of Multiple Output Voltages

PowerPath and Burst Mode are trademarks of Linear Technology Corporation.

RELATED PARTS

Description

With its SENSE pin at the source of Q11, the LTC1435 can
raise V

OUT

above V

(rated voltage) 5.5% once the main

TYPICAL APPLICATIO

SENSE

INTV

BOOST

OSC

SGND

PGND

RUN/SS

OSENSE

LTC1435

0.1

SENSE

0.033

L1*

*SUMIDA CDRH125-10
**IRC LR2010-01-R033-F

SUMIDA CD54-220

C3
4.7

16V

CMDSH-3

1559 TA04

D2
MBRS140T3

R5
20k
1%

R1
35.7k
1%

C5
1000pF

100pF

Q2
N-CH
Si4412DY

Q1
N-CHANNEL
Si4412DY

SFB

EXTV

35V

OSC

68pF

10k

0.1

330pF

C1
100pF

51pF

C2
0.1

OUT

3.3V

CTL

C11
1

6.3V

BACKUP
BATTERY
1.2V
NiCd

MAIN
BATTERY
4.5 TO 28V

Q11
P-CHANNEL
Si9424DY

R14
14k

LTC1559-3.3

L11

GND

RESET
PUSH-BUTTON

BAK

RESET

BACKUP

R15
100k

C12
1

RESET

BACKUP

OUT

100

10V

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900

FAX: (408) 434-0507

www.linear-tech.com

battery is restored. Thus, the LTC1559 does not use the PS
pin to sense the LTC1435's output during backup mode.
The PS pin is grounded in this case. Please refer to the
Applications Information section for more details.

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LTC1559CS-5

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: LTC1559CS-5