LTC3555 Linear Technology, LTC3555 Datasheet - Page 14

• Manufacturer Part Number: LTC3555
• Description: High Efficiency USB Power Manager + Triple Step-Down DC/DC
• Manufacturer: Linear Technology

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LTC3555
Introduction
The LTC3555 is a highly integrated power management IC
which includes a high effi ciency 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 or by an I
Designed specifi cally 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 allows the load current on V
the current drawn by the USB port without exceeding the
USB load specifi cations.
The PowerPath switching regulator and battery charger
communicate to ensure that the input current never violates
the USB specifi cations.
The ideal diode from BAT to V
power is always available to V
fi cient or absent power at V
An “always on” LDO provides a regulated 3.3V from avail-
able power at V
this LDO will be on at all times and can be used to supply
TIMING DIAGRAM
OPERATION
14
SDA
SCL
START
0
0
1
0
0
2
SDA
SCL
t
HD, STA
OUT
0
0
3
CONDITION
. Drawing very little quiescent current,
ADDRESS
START
1
1
4
0
0
2
5
C serial port or both.
t
LOW
BUS
0
0
6
OUT
OUT
t
r
.
1
1
7
t
HIGH
t
guarantees that ample
SU, DAT
even if there is insuf-
WR
0
0
8
t
f
ACK
9
OUT
A7
1
t
HD, DAT
A6
to exceed
2
I
A5
2
3
C Timing Diagram
DATA BYTE A
A4
4
REPEATED START
CONDITION
A3
5
up to 25mA.
The three general purpose switching regulators can be
independently enabled via either direct digital control or
by operating the I
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 signifi cantly reduced
quiescent current under light load conditions.
High Effi ciency Switching PowerPath Controller
Whenever V
ing regulator is enabled, power is delivered from V
V
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
track 0.3V above the battery. By keeping the voltage across
the battery charger low, effi ciency is optimized because
power lost to the linear battery charger is minimized. Power
available to the external load is therefore optimized.
A2
OUT
6
t
SU, STA
A1
7
via SW. V
t
HD, STA
A0
t
8
SP
ACK
BUS
9
OUT
B7
1
is available and the PowerPath switch-
2
C serial port. Under I
drives the combination of the external
B6
2
CONDITION
B5
3
STOP
DATA BYTE B
B4
4
t
SU, STO
t
BUF
B3
5
CONDITION
START
B2
6
3555 TD
2
B1
7
C control, two of
B0
8
ACK
9
OUT
BUS
STOP
will
3555f
to