BQ24740_07 Datasheet, PDF (25/32 Pages) Texas Instruments – Host-controlled Multi-chemistry Battery Charger with Low Input Power Detect

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bq24740
SLUS736 – DECEMBER 2006
APPLICATION INFORMATION (continued)
Figure 31 shows the measured input voltages and currents with different input capacitances. The voltage spike
drops by about 5 V after increasing Ci from 20 µF to 40 µF. The input voltage spike has been dramatically
damped by using a 47 F electrolytic capacitor.
Ci = 20 mF
Ci = 40 mF
( c ) C i = 4 9 mF ( 4 7 mF e l e c t r o l y t i c a n d 2 x mF ceramic)
Figure 31. Adapter DC Side Hot Plug-In With Various Input Capacitances
Since the input voltage to the IC is PVCC which is 0.7 V (diode voltage drop) lower than Vc during the adapter
insertion, a 40-µF input capacitance is normally adequate to keep the PVCC voltage well below the maximum
voltage rating under normal conditions. In case of a higher input stray inductance, the input capacitance may be
increased accordingly. An electrolytic capacitor will help reduce the input voltage spike due to its high ESR.
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