BQ24257 Datasheet, PDF (22/45 Pages) Texas Instruments – 2A Single Input I2C, Standalone Switch-Mode Li-Ion Battery Charger with Integrated Current Sense Resistor

bq24257
bq24258
SLUSBG0B – FEBRUARY 2013 – REVISED JULY 2013
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performance when regulating the voltage due to the simplification of the compensation when using current mode
control. The below transient response plot illustrates a 0 A to 2 A load step with 4.7 ms full cycle and 12% duty
cycle. A 3.9 V Li-Ion battery is used. The input voltage is set to 5 V, charge current is set to 0.5 A and the input
current is limited to 0.5 A. . Note that a high line impedance input supply was used to indicate a realistic input
scenario (adapter and cable). This is illustrated by the change in V_IN seen at the input of the IC.
The figure shows a ringing at both the input voltage and the input current. This is caused by the input current
limit speed up comparator.
Figure 18. 2A Load step Transient
AnyBoot Battery Detection
The bq24257, bq24258 family includes a sophisticated battery detection algorithm used to provide the system
with the proper status of the battery connection. The AnyBoot battery algorithm also guarantees the detection of
voltage based battery protectors that may have a long closure time (due to the hysteresis of the protection switch
and the cell capacity). The AnyBoot battery detection algorithm is utilizes a dual-voltage based detection
methodology where the system rail will switch between two primary voltage levels. The period of the voltage level
shift is 64ms and therefore the power supply rejection of the down-system electronics will see this shift as
essentially DC.
The AnyBoot algorithm has essentially 3 states. The 1^st state is used to determine if the device has terminated
with a battery attached. If it has terminated due to the battery not being present, then the algorithm moves to the
2^nd and 3^rd states. The 2^nd and 3^rd states shift the system voltage level between 4.2V and 3.72V. In each state
there are comparator checks to determine if a battery has been inserted. The two states guarantees the
detection of a battery even if the voltage of the cell is at the same level of the comparator thresholds. The
algorithm will remain in states 2 and 3 until a battery has been inserted. The flow diagram details for the Anyboot
algorithm are shown in Figure 19.
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