Termination

Regulation

Current

Regulation

voltage

Precharge

Phase

Current Regulation

Phase

Voltage Regulation

Phase

Charge Current

Battery

Voltage

System Voltage

Linear Charge

to Maintain

Minimum

System

Voltage

50mA Linear Charge

to Close Pack

Protector

Battery FET is ON

Battery

FET

is OFF

bq24278

SLUSB04 – JUNE 2012

www.ti.com

DETAILED DESCRIPTION

The bq24278 is a highly integrated single cell Li-Ion battery charger and system power path management

devices targeted for space-limited, portable applications with high capacity batteries. The power path

management feature allows the bq24278 to power the system from a high efficiency DC to DC converter while

simultaneously and independently charging the battery. The charger monitors the battery current at all times and

reduces the charge current when the system load requires current above the input current limit. This allows for

proper charge termination and enables the system to run with a defective or absent battery pack. Additionally,

this enables instant system turn-on even with a totally discharged battery or no battery. The power-path

management architecture also permits the battery to supplement the system current requirements when the

adapter cannot deliver the peak system currents. This enables the use of a smaller adapter. The battery is

charged in three phases: conditioning, constant current and constant voltage. In all charge phases, an internal

control loop monitors the IC junction temperature and reduces the charge current if the internal temperature

threshold is exceeded.

Charge Mode Operation

Charge Profile

Charging is done through the internal battery MOSFET. When the battery voltage is above 3.5V, the system

output (SYS) is connected to the battery to maximize the charging efficiency. There are 5 loops that influence the

charge current; constant current loop (CC), constant voltage loop (CV), thermal regulation loop, minimum system

process, all five loops are enabled and the dominant one takes control. The bq24278 supports a precision Li-Ion

or Li-Polymer charging system for single-cell applications. The minimum system output feature regulates the

battery. Figure 2 shows a typical charge profile including the minimum system output voltage feature.

Figure 2. Typical Charging Profile of bq24278

10

Submit Documentation Feedback

Copyright © 2012, Texas Instruments Incorporated

Product Folder Link(s) :bq24278