Datasheet

LTC3556
14
3556f
OPERATION
TIMING DIAGRAM
t
SU, DAT
t
HD, STA
t
HD, DAT
SDA
SCL
t
SU, STA
t
HD, STA
t
SU, STO
3556 TD
t
BUF
t
LOW
t
HIGH
START
CONDITION
REPEATED START
CONDITION
STOP
CONDITION
START
CONDITION
t
r
t
f
t
SP
ACK ACK
123
ADDRESS WR
456789123456789123456789
00 01 0 01 0
00010010
A7 A6 A5 A4 A3 A2 A1 A0 B7 B6 B5 B4 B3 B2 B1 B0
ACK
STOPSTART
SDA
SCL
DATA BYTE A DATA BYTE B
I
2
C Timing Diagram
Introduction
The LTC3556 is a highly integrated power management IC
which includes a high efficiency switch mode PowerPath
controller, a battery charger, an ideal diode, an always-on
LDO, two 400mA buck switching regulators and a 1A buck-
boost switching regulator. The entire chip is controllable
via an I
2
C serial port.
Designed specifically for USB applications, the PowerPath
controller incorporates a precision average input current
step-down switching regulator to make maximum use of
the allowable USB power. Because power is conserved,
the LTC3556 allows the load current on V
OUT
to exceed
the current drawn by the USB port without exceeding the
USB load specifications.
The PowerPath switching regulator and battery charger
communicate to ensure that the input current never violates
the USB specifications.
The ideal diode from BAT to V
OUT
guarantees that ample
power is always available to V
OUT
even if there is insuf-
ficient or absent power at V
BUS
.
An “always-on” LDO provides a regulated 3.3V from avail-
able power at V
OUT
. Drawing very little quiescent current,
this LDO will be on at all times and can be used to supply
up to 25mA.
The three switching regulators can be enabled together
in any desired sequence via the ENALL and SEQ pins
or can be independently enabled via the I
2
C serial port.
Under I
2
C control, one of the 400mA bucks and the 1A
buck-boost have adjustable set-points so that voltages
can be reduced when high processor performance is not
needed. Along with constant frequency PWM mode, all
three switching regulators have a low power burst-only
mode setting for significantly reduced quiescent current
under light load conditions. Additionally, the 400mA bucks
can be confi gured for automatic Burst Mode operation or
LDO mode.
High Efficiency Switching PowerPath Controller
Whenever V
BUS
is available and the PowerPath switch-
ing regulator is enabled, power is delivered from V
BUS
to
V
OUT
via SW. V
OUT
drives the combination of the external
load (including switching regulators 1, 2 and 3) and the
battery charger.
If the combined load does not exceed the PowerPath switching
regulator’s programmed input current limit, V
OUT
will track
0.3V above the battery (Bat-Track). By keeping the voltage
across the battery charger low, efficiency is optimized because
power lost to the linear battery charger is minimized. Power
available to the external load is therefore optimized.