A method for generating from a single supply voltage Vdd energy efficient supply voltages, comprising values of Vdd/6 and VDD/5 being symmetrical around ground voltage, comprising the following steps: providing an input voltage Vdd and a charge pump circuit, having a positive and a negative output node (OUTP, OUTN), comprising a digital controller, a set of switches (S0-S14), two flying capacitors (C1, C2), and two reservoir capacitors; setting output voltage modes desired on the digital controller comprising values of Vdd/6 and VDD/5 being symmetrical around ground voltage; setting the switches (S0-S14) in order to put voltages on both flying capacitors (C1, C2) and on at least one output port according to an equation describing a first phase of an actual output voltage mode of the charge pump comprising in either Vdd/5 mode or in Vdd/6 mode: the voltage across a first of said flying capacitors + the voltage across a second of said flying capacitors + a voltage of the positive output node (OUTP) = Vdd; setting switches (S0-S14) in order to put voltages on both flying capacitors (C1, C2) and on at least one output port according to an equation describing a second phase of an actual output voltage mode of the charge pump comprising, if Vdd/5 mode is set: the voltage across the first flying capacitor = a sum of the voltages on the positive and negative output nodes (OUTP, OUTN) + the voltage across the second flying capacitor, and if Vdd/6 mode is set: the voltage across the first flying capacitor = the voltage across the second flying capacitor + the voltage on the positive output node (OUTP); setting switches (S0-S14) in order to put voltages on both flying capacitors (C1,C2) and on one or more output port according to an equation describing a third phase of an actual output voltage mode of the charge pump comprising, if Vdd/5 mode is set: the voltage across the second flying capacitor = the voltage of the negative output node (OUTN) and, if Vdd/6 mode is set: the voltage across the first flying capacitor = the voltage across the second flying capacitor + the voltage on the negative output node (OUTN); setting switches (S0-S14) in order to put voltages on both flying capacitors (C1,C2) and on one or more output port according to an equation describing a fourth phase of an actual output voltage mode of the charge pump comprising, if Vdd/5 mode is set: the voltage across the second flying capacitor = the voltage of the positive output node (OUTP) and, if Vdd/6 mode is set: the voltage across the second flying capacitor = the voltage on the positive output node (OUTP) + the voltage on the negative output node(OUTN); go to step if charge pump is on, else go to step; go to step if output voltage mode is to be changed, else go to step; change output voltage mode and go to step; and end. providing an input voltage Vdd and a charge pump circuit, having a positive and a negative output node (OUTP, OUTN), comprising a digital controller, a set of switches (S0-S14), two flying capacitors (C1, C2), and two reservoir capacitors; setting output voltage modes desired on the digital controller comprising values of Vdd/6 and VDD/5 being symmetrical around ground voltage; setting the switches (S0-S14) in order to put voltages on both flying capacitors (C1, C2) and on at least one output port according to an equation describing a first phase of an actual output voltage mode of the charge pump comprising in either Vdd/5 mode or in Vdd/6 mode: the voltage across a first of said flying capacitors + the voltage across a second of said flying capacitors + a voltage of the positive output node (OUTP) = Vdd; setting switches (S0-S14) in order to put voltages on both flying capacitors (C1, C2) and on at least one output port according to an equation describing a second phase of an actual output voltage mode of the charge pump comprising, if Vdd/5 mode is set: the voltage across the first flying capacitor = a sum of the voltages on the positive and negative output nodes (OUTP, OUTN) + the voltage across the second flying capacitor, and if Vdd/6 mode is set: the voltage across the first flying capacitor = the voltage across the second flying capacitor + the voltage on the positive output node (OUTP); setting switches (S0-S14) in order to put voltages on both flying capacitors (C1,C2) and on one or more output port according to an equation describing a third phase of an actual output voltage mode of the charge pump comprising, if Vdd/5 mode is set: the voltage across the second flying capacitor = the voltage of the negative output node (OUTN) and, if Vdd/6 mode is set: the voltage across the first flying capacitor = the voltage across the second flying capacitor + the voltage on the negative output node (OUTN); setting switches (S0-S14) in order to put voltages on both flying capacitors (C1,C2) and on one or more output port according to an equation describing a fourth phase of an actual output voltage mode of the charge pump comprising, if Vdd/5 mode is set: the voltage across the second flying capacitor = the voltage of the positive output node (OUTP) and, if Vdd/6 mode is set: the voltage across the second flying capacitor = the voltage on the positive output node (OUTP) + the voltage on the negative output node(OUTN); go to step if charge pump is on, else go to step; go to step if output voltage mode is to be changed, else go to step; change output voltage mode and go to step; and end.