Battery charger for preventing charging currents from overshooting during mode transition and method thereof

A battery charger for charging a battery, comprising:

• a charging regulation circuit having an input terminal, a control terminal, and an output terminal, wherein the input terminal is for being coupled to a power supplier, the output terminal is coupled to a node N1, the control terminal is coupled to a node N5, and the charging regulation circuit outputs a charging current whose amount is regulated based on a regulation signal at the control terminal;
• a first current sensing unit having a first and a second input terminals and a first and a second output terminals, wherein the first input terminal is coupled to the node N1, the first output terminal is coupled to a node N2 for being coupled to the battery, the second input terminal is inputted by a first reference signal, the second output terminal is coupled to a node N3, and the first current sensing unit senses a current level on a path from the node N1 to the node N2 and outputs an error signal at the second output terminal based on the current level and the first reference signal;
• an operational amplifier having a positive input terminal coupled to the node N2, a negative input terminal coupled to a node N4, and an output terminal coupled to the node N5 for generating the regulation signal;
• a comparator for comparing a second reference signal with the voltage of the node N2, and generating an enabling signal;
• a first switch unit for electrically coupling the second output terminal of the first current sensing unit to the node N5 when the enabling signal is not active;
• a second switch unit for electrically coupling the output terminal of the operational amplifier to the node N5 when the enabling signal is active;
• and
• a third switch unit for electrically coupling the comparator to the second reference signal when the enabling signal is active, or for electrically coupling the comparator to the node N4 when the enabling signal is not active;
• and
• a reference voltage generator having an input terminal coupled to the node N3 and an output terminal coupled to the node N4, comprising:
• an ADC for converting the error signal outputted by the first current sensing unit to a digital signal;
• and
• a DAC for converting the digital signal to a reference voltage, wherein the DAC decreases the reference voltage when the enabling signal is active and the error signal indicates that the current level on the path from the node N1 to the node N2 is greater than the first reference signal:
• wherein the voltage at the node N2 reflects the battery voltage of the battery.