5
LTC4410
sn4410 4410fs
OPERATIO
U
The LTC4410 manages the total current consumption
between a battery charger and a USB portable device. In
a system using the LTC4410, a battery charger can be set
up to charge at the maximum available current from the
USB port without any need to reserve current for the
device load. As the USB device current increases, the
LTC4410 decreases the battery charge current so as not
to exceed the maximum allowable current from the USB
port. This allows for simultaneous battery charging and
device operation. The LTC4410 can only reduce the bat-
tery charge current to zero. It is the responsibility of the
USB device load to not exceed the USB power limits.
The LTC4410 uses an internal power MOSFET to sense
load current. This MOSFET is held off when V
OUT
> V
IN
or
V
IN
< 4.2V (typ). A replica of the I
VOUT
current equal to
I
VOUT
/1000 is sourced out of the CHP pin with an accuracy
of ±6%. This current can be summed into the PROG node
of a battery charger to reduce the charge current. The
LTC4410 is primarily designed to interface with battery
chargers that use a program pin to set the maximum
charge current, with a charge current to program pin
current ratio of 1000:1. The voltage on CHP can be
externally monitored to signal overcurrent conditions.
When V
IN
> 4.2V, the internal USB present comparator
forces the USBP pin high. This signal can be used to detect
when the USB voltage is present and drive an external
switch to connect or disconnect a battery from the USB
peripheral.
The MODE pin controls the state of an internal 370µA
current reference (I
REF
). When active (MODE pin low), the
total current sourced out of CHP is I
VOUT
/1000 +I
REF
. The
primary function of the current reference is to offset the
battery charger charge current for 100mA mode. When
MODE is high, the current reference is disabled. The total
current out of CHP with MODE high is I
VOUT
/1000. The
MODE controlled current offset makes it possible to con-
figure the battery charger and the LTC4410 to support the
USB specification 1.0 and 2.0 required 100mA and 500mA
modes of operation.
The low quiescent current (80µA, when MODE is high) of
the LTC4410 makes the system easily compliant with the
USB specifications 1.0 and 2.0 SUSPEND MODE current
consumption requirements.
When V
OUT
> V
IN
, the LTC4410 transitions to low power
mode, draining 1µA (typical) from the Lithium-Ion battery.
This condition occurs when the USB device is operating
off of its internal battery and not connected to the USB
port.
