LINEAR TECHNOLOGY LTC3556, LTC3566, LTC3567 Technical data

L DESIGN FEATURES

Li-Ion

0.8V TO 3.6V/400mA

3.3V/25mA

0.8V TO 3.6V/400mA

0.8V TO 3.6V/1A

RST

2

OPTIONAL

0V

T

TO OTHER
LOADS

+

LTC3555/LTC3555-X

TRIPLE

HIGH EFFICIENCY

STEP-DOWN

SWITCHING

REGULATORS

I2C PORT

ALWAYS ON LDO

MEMORY

RTC/LOW
POWER LOGIC

I2C

CORE

I/O

µPROCESSOR

USB/WALL

4.35V TO 5.5V

CHARGE

ENABLE

CONTROLS

USB COMPLIANT

STEP-DOWN
REGULATOR

CC/CV

BATTERY

CHARGER

5

1

2

3

CURRENT
CONTROL

New Family of Integrated Power
Controllers Combine Fast Battery
Charging, PowerPath Control and
Efficient DC/DC Converters in
Less Than 20mm2

Introduction

The quickest way to build an efficient
power system for a battery-powered
portable application is to use an
IC that combines all power control
functions into a single chip, namely a
Power Management Integrated Circuit
(PMIC). PMICs seamlessly manage
power flow from various power sources
(wall adapters, USB and batteries) to
power loads (device systems and the
charging battery), while maintaining
current limits where required (such
as that specified for USB). To this
end, PMICs typically feature built-in
PowerPath™ control, DC/DC conver-

Table 1. Power management ICs with Li-ion/polymer battery chargers

PowerPath

Part Number

LTC3555/-1/-3 Switching I2C 1A, 400mA × 2 25mA

Topology Interface

Figure 1. High efficiency PowerPath manager and triple step-down regulator

Integrated Converters and Load Current Capabilities

by Sam Nork

PackageBuck Buck-Boost Boost LDO

4mm × 5mm

QFN-28

LTC3556 Switching I2C 400mA × 2 1A 25mA

LTC3566 Switching 1A 25mA

LTC3567 Switching I2C 1A 25mA

LTC3586* Switching 400mA × 2 1A 0.8A 20mA

LTC3557/-1 Linear 600mA, 400mA × 2 25mA

Linear Technology Magazine • September 2008

LTC3455 Linear 600mA, 400mA Controller

LTC3558 400mA 400mA

LTC3559/-1 400mA × 2

*For an application of the LTC3586 see “Complete Power Solution for Digital Cameras and Other Complex Compact Portable Applications” in this issue

4

4mm × 5mm

QFN-28

4mm × 4mm

QFN-24

4mm × 4mm

QFN-24

4mm × 6mm

QFN-38

4mm × 4mm

QFN-28

4mm × 4mm

QFN-24

3mm × 3mm

QFN-20

3mm × 3mm

QFN-16

DESIGN FEATURES L

Li-Ion

PGOODALL

0.8V TO 3.6V/400mA

3.3V/25mA

2.5V to 3.3V/1A

0.8V TO 3.6V/400mA

OPTIONAL

0V

T

TO OTHER
LOADS

+

LTC3556

DUAL HIGH EFFICIENCY

BUCKS

HIGH EFFICIENCY

BUCK-BOOST

I2C PORT

ALWAYS ON LDO

MEMORY
CORE
µP

RTC/LOW
POWER LOGIC

HDD/IO

3556 TA01

USB/WALL

4.5V TO 5.5V

CHARGE

I2C

USB COMPLIANT

STEP-DOWN
REGULATOR

CC/CV

BATTERY

CHARGER

SEQ

ENALL

3

1

2

3

40

50

60

70

80

30

20

10

0

90

100

V

IN3

(V)

2.7

EFFICIENCY (%)

3.1

3.5 3.9 4.3 4.7

V

OUT3

= 3.3V

TA = 27°C

I

OUT3

= 200mA

I

OUT3

= 50mA

I

OUT3

= 1000mA

BATTERY VOLTAGE (V)

2.8

0

CHARGE CURRENT (mA)

200

3.2

3.6

3.8

100

700

400

500

600

300

3

3.4

4

4.2

BATTERY CHARGE CURRENT

500mA USB CURRENT LIMIT

EXTRA CURRENT
FOR FASTER CHARGING

V

BUS

= 5V
5X MODE
BATTERY CHARGER PROGRAMMED FOR 1A

sion and battery charging functions.
PMICs can be applied in everything
from consumer electronics such as
MP3 players and Bluetooth headsets
to specialized portable medical and
industrial equipment.

Table 1 shows the wide variety of
integrated charger and DC/DC com­binations now available from Linear
Technology. The latest additions to
the family, the LTC3555, LTC3556,
LTC3566, LTC3567 and LTC3586, are
primarily targeted toward relatively
high power Li-Ion applications and
contain blocks capable of high effi­ciency at high current levels. (To see
an application of the LTC3586, see
“Complete Power Solution for Digital
Cameras and Other Complex Compact
Portable Applications” in the Design
Ideas section of this issue.)

The most noteworthy feature of the
new parts is the use of a proprietary
switching PowerPath design, which
improves efficiency over linear power
path or battery fed solutions.

Switching PowerPath Control
Efficiently Harnesses
Available External Power

To speed up charging, some of Linear’s
new PMICs employ a unique current
limited synchronous buck switch­ing charger architecture that uses
more power from the USB or adapter
than other topologies. This is a big
improvement over battery fed and
linear PowerPath control schemes.
(For a more detailed description of
the switching PowerPath architecture,

on” capability if the battery is dead or
missing (as long as the load current
is less than the input current limit).
However, neither a linear charger nor
linear power manager is well-suited
for high current charging due to poor
efficiency under certain conditions.

power, but charging/powering from
the USB host is complicated by the
host’s 2.5W limit. To take advantage of
the limited USB power, all components

Figure 2. Switching power manager charge
current vs battery voltage with a 500mA input
current limit. Peak charge current = 700mA.

in the power path must be as efficient
as possible.

is a battery-tracking (Bat-Track™)
see the cover article in the June 2008
issue of Linear Technology magazine
titled “Speed Up Li-ion Battery Charg­ing and Reduce Heat with a Switching
PowerPath Manager.”)

For instance, portable products
with large capacity batteries (1Ahr
plus) face a direct tradeoff between
charge time and charger power dis­sipation—especially when a linear
charging method is used. At relatively
low charge currents, a linear charger
dissipates a modest amount of power,
but at currents required to quickly
charge high capacity batteries, a linear
charger can dissipate 2W or more.

A switching PowerPath topology is
an improvement over the commonly

synchronous buck design with logic
programmable input current limit to
ensure USB compatibility. When USB
or adapter power is available, the
LTC35xx power manager generates a
V
The 300mV difference voltage is suf­ficient to keep the battery charger
just out of dropout and deliver the
programmed charge current at high
efficiency. As with linear power manag­ers, the load current is provided first,
and current that is left over is directed
to the battery. Input current limit is
controlled via an external resistor to
set absolute current and two logic
pins to control the ratio (e.g. 100mA,

500mA, 1A and Suspend).
used linear PowerPath topology, and
both are an improvement over battery
fed applications. A linear PowerPath
powers the application directly from
an external source rather than from
the battery itself and provides “instant

with a completely discharged battery

is achievable vs 60% or so for a linear

charger. Or said another way, the

switching power path dissipates only

50% of the power dissipated by a linear

USB is now a common source of

A key attribute in these new PMICs

supply equal to V

OUT

+ 300mV.

BAT

Charging efficiency of over 80%

Linear Technology Magazine • September 2008

Figure 3. 1A buck-boost efficiency vs VIN (LTC3556, LTC3566/7, LTC3586)

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