Voltage converter with combined buck converter and capacitive voltage divider

An electronic device, comprising:

• a combined buck converter and capacitor voltage divider, comprising:
• a first capacitor coupled between a reference node and a first power node which develops a first source voltage;
• a second capacitor coupled between an input node and either one of said reference node and said first power node;
• a third capacitor coupled between first and second intermediate nodes;
• a switch circuit, comprising a first switch having current terminals coupled between said input node and said first intermediate node, a second switch having current terminals coupled between said first intermediate node and said first source node, a third switch having current terminals coupled between said first source node and said second intermediate node, and a fourth switch having current terminals coupled between said second intermediate node and said reference node;
• an inductor having a first end coupled to said second intermediate node and having a second end forming a second power node which develops a second source voltage;
• a fourth capacitor coupled between said second power node and said reference node;
• a battery charger and controller operative to selectively couple an external power source node to said input node when said external power source node receives a DC voltage to provide an input voltage on said input node, to selectively couple a rechargeable battery node to said first source node when said external power source node does not receive said DC voltage, and to control said switch circuit based on a pulse width modulation signal to regulate said second source voltage to a predetermined voltage level;
• wherein when said external power source node receives said DC voltage, said battery charger and controller controls said switch circuit based on said pulse width modulation signal to toggle coupling of said first intermediate node between said input node and said first output node and to toggle coupling of said second intermediate node between said first output node and said reference node;
• and
• wherein when said external power source node does not receive said DC voltage, said battery charger and controller turns off said first and second switches and controls said third and fourth switches based on said pulse width modulation signal to toggle coupling of said second intermediate node between said first source node and said reference node;
• and
• functional circuitry which receives said first and second source voltages and which performs functions of the electronic device.

A method of operating a power circuit providing first and second output voltages, comprising:

• coupling a first switch between an input node and a first intermediate node, coupling a second switch between the first intermediate node and a first output node which develops the first output voltage, coupling a third switch between the first output node and a second intermediate node, and coupling a fourth switch between the second intermediate node and a reference node;
• coupling a capacitor loop between the input node, the reference node, and the first output node;
• coupling a fly capacitor between the first and second intermediate nodes;
• coupling an inductor between the second intermediate node and a second output node which develops the second output voltage;
• controlling the duty cycle of a pulse width modulation signal for regulating the second output voltage to a predetermined level;
• detecting whether a DC voltage is provided to an external power node;
• when the DC voltage is provided to the external power node, coupling the external power node to the input node and controlling the first, second, third and fourth switches based on the pulse width modulation signal to toggle coupling of the first intermediate node between the input node and the first output node and to toggle coupling of the second intermediate node between the first output node and the reference node;
• and
• when the DC voltage is not provided to the external power node, coupling a battery node to the first output node, turning off the first and second switches, and controlling the third and fourth switches based on the pulse width modulation signal to toggle coupling of the second intermediate node between the first output node and the reference node.