LTC3556_15 Datasheet, PDF (14/36 Pages) Linear Technology – High Effi ciency USB Power Manager with Dual Buck and Buck-Boost DC/DCs

LTC3556
TIMING DIAGRAM
I²C Timing Diagram
00
START
SDA
00
ADDRESS
0100
WR
10
DATA BYTE A
A7 A6 A5 A4 A3 A2 A1 A0
DATA BYTE B
B7 B6 B5 B4 B3 B2 B1 B0
0 1 0 0 1 0 ACK
ACK
ACK
STOP
SCL
123456789123456789123456789
SDA
t_LOW
t_{SU, DAT}
SCL
t_{HD, STA}
START
CONDITION
t_HIGH
t_r
t_f
t_{HD, DAT}
t_{SU, STA}
t_{HD, STA}
t_SP
REPEATED START
CONDITION
t_BUF
t_{SU, STO}
3556 TD
STOP
CONDITION
START
CONDITION
OPERATION
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 I²C 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.
14
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 I²C serial port.
Under I²C 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 configured 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.
3556f