Charging Control

TPS65573

Figure 5 shows a timing diagram at beginning/ending. The TPS65573 provides three comparators to control the

SW.

Figure 5. Beginning/Ending Timing

power SW turns OFF.

After the power SW turns OFF, the spike voltage occurs immediately because of leakage inductance at the

primary side. It might cause the power SW to break. To avoid this, the leakage inductance should be reduced as

much as possible.

When the power SW is OFF, the magnetic energy in the transformer starts discharging from the primary side to

primary side to compare it with the VBAT voltage. The kickback voltage increases rapidly until the diode placed

at secondary side turns ON. The diode turns ON when the voltage of secondary side of the transformer reaches

more than the voltage of the output capacitor. After the diode turns ON, the kickback voltage is almost stable

until the magnetic energy at the primary side discharges completely.

After the discharge stops, the small amount of energy left in the transformer is released via parasitic paths, and

the kickback voltage reaches almost zero voltage. During this period, U2 makes the power SW turn ON when

stops the charging operation. After detection, XFULL goes to low level to indicate charge completion. After

charge completion, the TPS65573 immediately goes into disable mode with the internal ENA automatically

turning to a low level. The purpose is to save the consumption power.

Copyright © 2009, Texas Instruments Incorporated

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