BQ24250C_15 Datasheet, PDF (16/46 Pages) Texas Instruments – bq24250C 2A Single Input I2C, Standalone Switch-Mode Li-Ion Battery Charger with Power-Path Management

bq24250C
SLUSBY7 – JULY 2014
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8.3 Feature Description
8.3.1 Dynamic Power Path Management
The bq24250C features a SYS output that powers the external system load connected to the battery. This output
is active whenever a valid source is connected to IN or BAT. The following discusses the behavior of SYS with a
source connected to the supply or a battery source only.
When a valid input source is connected to the input and the charge is enabled, the charge cycle is initiated. In
case of VBAT > ~3.5V, the SYS output is connected to VBAT. If the SYS voltage falls to VMINSYS, it is
regulated to the VSYSREG threshold to maintain the system output even with a deeply discharged or absent
battery. In this mode, the SYS output voltage is regulated by the buck converter and the battery FET is linearly
regulated to regulate the charge current into the battery. The current from the supply is shared between charging
the battery and powering the system load at SYS.
The dynamic power path management (DPPM) circuitry of the bq24250C monitors the current limits continuously
and if the SYS voltage falls to the VMINSYS voltage, it adjusts charge current to maintain the minimum system
voltage and supply the load on SYS. If the charge current is reduced to zero and the load increases further, the
bq24250C enters battery supplement mode. During supplement mode, the battery FET is turned on and the
battery supplements the system load.
If the battery is ever 5% above the regulation threshold, the battery OVP circuit shuts the PWM converter off and
the battery FET is turned on to discharge the battery to safe operating levels. Battery OVP FAULT is shown in
the I2C FAULT registers.
When no input source is available at the input and the battery is connected, the battery FET is turned on similar
to supplement mode. The battery must be above VBATUVLO threshold to turn on the SYS output. In this mode,
the current is not regulated;
8.3.2 Production Test Mode
To aid in end mobile device product manufacturing, the bq24250C includes a Production Test Mode (PTM),
where the device is essentially a DC-DC buck converter. In this mode the input current limit to the charger is
disabled and the output current limit is limited only by the inductor cycle-by-cycle current (e.g. 3.5A). The PTM
mode can be used to test systems with high transient loads such as GSM transmission without the need of a
battery being present.
As a means of safety, the Anyboot algorithm determines if a battery is not present at the output prior to enabling
the PTM mode. If a battery is present and the software attempts to enter PTM mode, the device will not enable
PTM mode.
8.3.3 AnyBoot Battery Detection
The bq24250C includes a sophisticated battery detection algorithm used to provide the system with the proper
status of the battery connection. The AnyBoot battery algorithm also ensures 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 utilizes a dual-voltage based detection methodology where
the system rail switches 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 detects 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 ensure 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 14.
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