Datasheet

LTC4155
18
4155fc
OPERATION
Introduction
The LTC4155 is an advanced I
2
C controlled power man-
ager and Li-Ion/Polymer battery charger designed to
efficiently transfer up to 15W from a variety of sources
while minimizing power dissipation and easing thermal
budgeting constraints. By decoupling V
OUT
and the battery,
the innovative instant-on PowerPath architecture ensures
that the application is powered immediately after external
voltage is applied, even with a completely dead battery,
by prioritizing power to the application.
Since V
OUT
and the battery are decoupled, the LTC4155
includes an ideal diode controller. The ideal diode from
the battery to V
OUT
guarantees that ample power is always
available to V
OUT
even if there is insufficient or absent
power at V
BUS
.
The LTC4155 includes a monolithic step-down switch-
ing battery charger for USB support, wall adapters and
other 5V sources. By incorporating a unique input current
measurement and control system, the switching charger
interfaces seamlessly to wall adapters and USB ports
without requiring application software to monitor and
adjust system loads. Because power is conserved, the
LTC4155 allows the load current on V
OUT
to exceed the
current drawn by the USB port or wall adapter, making
maximum use of the allowable power for battery charging
without exceeding the USB or wall adapter power delivery
specifications. A wide range of input current settings as
well as battery charge current settings are available for
selection by I
2
C.
Using only one inductor, the switching PowerPath can
operate in reverse, boosting the battery voltage to provide
5V power at its input pin for USB On-The-Go applications.
In the USB-OTG mode, the switching regulator supports
USB high power loads up to 500mA. Protection circuits
ensure that the current is limited and ultimately the channel
is shut down if a fault is detected on the USB connector.
To support USB low power mode, the LTC4155 can deliver
power to the external load and charge the battery through
a linear regulator while limiting input current to less than
100mA.
The LTC4155 also features a combination overvoltage
protection circuit/priority multiplexer which prevents
damage to its input caused by accidental application of
high voltage and selects one of two high power input
connectors based on priority.
A thermistor measurement subsystem periodically
monitors and reports the battery’s thermistor value via
the onboard I
2
C port. The same circuit then reports when
dangerous battery temperatures are reached and can
autonomously pause charging and optionally enable a bat-
tery safety conditioner. Refer to Overtemperature Battery
Conditioner in the Operation section for further details.
To minimize battery drain when a device is connected to a
suspended USB port, an LDO from V
BUS
to V
OUT
provides
the allowable USB suspend current to the application.
An interrupt subsystem can be enabled to alert the host
microprocessor of various status change events so that
system parameters can be varied as needed by system
software. Several status change event categories are
maskable for maximum flexibility.
To eliminate battery drain between manufacture and sale,
a ship-and-store feature reduces the already low battery
standby current to nearly zero and optionally disconnects
power from downstream circuitry.
An input undervoltage amplifier optionally prevents the
input voltage from decreasing below 4.3V when a resistive
cable or current limited supply is providing input power
to the LTC4155.
Finally, the LTC4155 has considerable adjustability built
in so that power levels and status information can be
controlled and monitored via the simple 2-wire I
2
C port.
Input Current-Limited Step-Down Switching Charger
Power delivery from V
BUS
to V
OUT
is controlled by a
2.25MHz constant-frequency step-down switching regu-
lator. The switching regulator reduces output power in
response to one of six regulation loops, including battery
voltage, battery charge current, output voltage, input cur-
rent, input undervoltage, and external PMOS charger FET
power dissipation. For USB low power (100mA) and USB
suspend (2.5mA) modes, the switching regulator is dis-
abled and power is transmitted through a linear regulator.