Datasheet
bq24155
www.ti.com
SLUS942 –FEBRUARY 2010
DETAILED FUNCTIONAL DESCRIPTION
For a current limited power source, such as a USB host or hub, a high efficiency converter is critical to fully use
the input power capacity for quickly charging the battery. Due to the high efficiency for a wide range of input
voltages and battery voltages, the switch mode charger is a good choice for high speed charging with less power
loss and better thermal management than a linear charger.
The bq24155 is a highly integrated synchronous switch-mode charger, featuring integrated FETs and small
external components, targeted at extremely space-limited portable applications powered by 1-cell Li-Ion or
Li-polymer battery pack.
The bq24155 has two operation modes: charge mode and high impedance mode. In charge mode, the bq24155
supports a precision Li-ion or Li-polymer charging system for single-cell applications. In high impedance mode,
the bq24155 stops charging and operates in a mode with low current from VBUS or battery, to effectively reduce
the power consumption when the portable device in standby mode. Through the proper control, bq24155
achieves the smooth transition among the different operation modes.
CHARGE MODE OPERATION
Charge Profile
In charge mode, bq24155 has four control loops to regulate input current, charge current, charge voltage and
device junction temperature, as shown in Figure 11. During the charging process, all four loops are enabled and
the one that is dominant takes control. The bq24155 supports a precision Li-ion or Li-polymer charging system
for single-cell applications. Figure 13(a) indicates a typical charge profile without input current regulation loop. It
is the traditional CC/CV charge curve, while Figure 13(b) shows a typical charge profile when input current
limiting loop is dominant during the constant current mode. In this case, the charge current is higher than the
input current so the charge process is faster than the linear chargers. For bq24155, the input current limits, the
charge current, termination current, and charge voltage are all programmable using I
2
C interface.
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