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LTC4155

4155fc

OPERATION

Introduction

The LTC4155 is an advanced I2C 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 VOUTandthebattery,

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 VOUT and the battery are decoupled, the LTC4155

includes an ideal diode controller. The ideal diode from

the battery to VOUT guarantees that ample power is always

available to VOUT even if there is insufficient or absent

power at VBUS.

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 VOUT 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 I2C.

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 I2C 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 VBUS to VOUT 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 I2C port.

Input Current-Limited Step-Down Switching Charger

Power delivery from VBUS to VOUT 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.

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