BQ24100_10 Datasheet, PDF (30/40 Pages) Texas Instruments – SYNCHRONOUS SWITCHMODE, LI-ION AND LI-POLYMER CHARGE-MANAGEMENT IC WITH INTEGRATED POWER FETs ( bqSWITCHER™)

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bq24113, bq24113A, bq24115
SLUS606O – JUNE 2004 – REVISED MARCH 2010
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Precharge: The current is low in precharge; so, the bottom synchronous FET turns off after its minimum on-time
which explains the step between Ⅹ0 V and -0.5 V. When the bottom FET and top FET are off, the current
conducts through the body diode of the bottom FET which results in a diode drop below the ground potential.
The initial negative spike is the delay turning on the bottom FET, which is to prevent shoot-through current as the
top FET is turning off.
Fast Charge: This is captured during the constant-current phase. The two negative spikes are the result of the
short delay when switching between the top and bottom FETs. The break-before-make action prevents current
shoot-through and results in a body diode drop below ground potential during the break time.
Charge during Voltage Regulation and Approaching Termination: Note that this waveform is similar to the
precharge waveform. The difference is that the battery voltage is higher so the duty cycle is slightly higher. The
bottom FET stays on longer because there is more of a current load than during precharge; it takes longer for the
inductor current to ramp down to the current threshold where the synchronous FET is disabled.
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