LTC3555 Datasheet, PDF (14/32 Pages) Linear Technology – High Effi ciency USB Power Manager + Triple Step-Down DC/DC

LTC3555/LTC3555-X
TIMING DIAGRAM
ADDRESS
WR
00 010010
DATA BYTE A
A7 A6 A5 A4 A3 A2 A1 A0
DATA BYTE B
B7 B6 B5 B4 B3 B2 B1 B0
START
SDA
0 0 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}
3555 TD
STOP
CONDITION
START
CONDITION
OPERATION
Introduction
The LTC3555 family are highly integrated power manage-
ment ICs which include a high efficiency switch mode
PowerPath controller, a battery charger, an ideal diode,
an always-on LDO and three general purpose step-down
switching regulators. The entire chip is controlled by either
direct digital control, by an I²C serial port or both.
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
LTC3555 family 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
available 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 general purpose switching regulators can be
independently enabled via either direct digital control or
by operating the I²C serial port. Under I²C control, two of
the three switching regulators 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 as well as automatic Burst
Mode operation and LDO modes for significantly reduced
quiescent current under light load conditions.
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 (switching regulators 1, 2 and 3) and the battery
charger.
If the combined load does not exceed the PowerPath switch-
ing regulator’s programmed input current limit, V_OUT will
track 0.3V above the battery. 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.
3555fd