BQ24230 Datasheet, PDF (26/33 Pages) Texas Instruments – USB-FRIENDLY LITHIUM-ION BATTERY CHARGER AND POWER-PATH MANAGEMENT IC

bq24230
bq24232
SLUS821A – OCTOBER 2008 – REVISED DECEMBER 2008 .......................................................................................................................................... www.ti.com
Half-Wave Adapters
Some low-cost adapters implement a half rectifier topology, which causes the adapter output voltage to fall below
the battery voltage during part of the cycle. To enable operation with low-cost adapters under those conditions,
the bq2407x family keeps the charger on for at least 20 ms (typical) after the input power puts the part in sleep
mode. This feature enables use of external low-cost adapters using 50-Hz networks.
Sleep Mode
After entering sleep mode for >20 ms, the internal FET connection between the IN and OUT pin is disabled and
pulling the input to ground does not discharge the battery, other than the leakage on the BAT pin. If the user has
a full 1000-mAHr battery and the leakage is 10 µA, then it takes 1000 mAHr/10 µA = 100000 hours (11.4 years)
to discharge the battery. The battery’s self-discharge is typically 5 times higher.
Layout Tips
• To obtain optimal performance, the decoupling capacitor from IN to GND (thermal pad) and the output filter
capacitors from OUT to GND (thermal pad) must be placed as close as possible to the bq2423x, with short
trace runs to both IN, OUT, and GND (thermal pad).
• All low-current GND connections must be kept separate from the high-current charge or discharge paths from
the battery. Use a single-point ground technique incorporating both the small signal ground path and the
power ground path.
• The high current charge paths into the IN pin and from the OUT pin must be sized appropriately for the
maximum charge current in order to avoid voltage drops in these traces.
• The bq2423x family is packaged in a thermally enhanced MLP package. The package includes a thermal pad
to provide an effective thermal contact between the IC and the printed-circuit board (PCB); this thermal pad is
also the main ground connection for the device. Connect the thermal pad to the PCB ground connection. Full
PCB design guidelines for this package are provided in the application report entitled: QFN/SON PCB
Attachment (SLUA271).
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