LTC4055 Linear Technology, LTC4055 Datasheet - Page 11

• Manufacturer Part Number: LTC4055
• Description: USB Power Controller and Li-Ion Linear Charger
• Manufacturer: Linear Technology

OPERATIO
The LTC4055 is a complete PowerPath controller for
battery-powered USB applications. The LTC4055 is de-
signed to provide device power and Li-ion battery charg-
ing from the USB V
as specified in the USB specification. This is accomplished
by reducing battery charge current as output/load current
is increased. In this scenario, the available bus current is
maximized in an effort to minimize battery charge time.
An ideal diode function provides power from the battery
when output/load current exceeds the input current limit
set for the part or when input power is removed. The
advantage to powering the load through the ideal diode
(rather than connecting the load directly to the battery) is
that when the bus is connected and the battery is fully
charged, the battery remains fully charged until bus power
is removed. Once bus power is removed the output drops
until the ideal diode is forward biased. The forward biased
ideal diode will then provide the output power to the load
from the battery.
V
BUS
AC
U
BUS
4
1
5
IN1
WALL
1V
IN2
while maintaining the current limits
–
+
INPUT CHARGER
CONTROL
ENABLE
Figure 1. Simplified Block Diagram—PowerPath
UVLO
CURRENT LIMIT
CONTROL
ENABLE
Another advantage to powering the load from the bus
when the bus is available is in cases where the load is a
switching regulator. The input power to a switching regu-
lator can be thought of as constant. A higher voltage
across a constant power load will require less current.
Less load current in USB applications means more avail-
able charge current. More charge current translates to
shorter charge times.
The LTC4055 also has the ability to accommodate power
from a wall adapter. Wall adapter power can be connected
to the output (load side) of the LTC4055 through an
external device such as a power Schottky or FET, as shown
in Figure 1. The LTC4055 has the unique ability to use the
output, which is powered by the wall adapter, as an
alternate path to charge the battery while providing power
to the load. A wall adapter comparator on the LTC4055 can
be configured to detect the presence of the wall adapter
and shut off the connection to the USB to prevent reverse
conduction out to the bus.
OUTPUT CHARGER
CONTROL
ENABLE
IDEAL
OUT
BAT
3
2
4055 F01
LTC4055
LOAD
+
Li-Ion
11
4055p