Optimized control of the "flying"-capacitor operating voltage in "gear-box"-charge-pumps-the key factor for a smooth operation

Traditional regulated charge-pumps have the basic problem that their efficiency is directly coupled to the ratio of input to output voltage. A charge-pump topology consisting of more than one "flying" capacitor with a flexible capacitor arrangement between charge and discharge phase of the converter can overcome this limitation. The most critical situation for such a "gear-box" SC-converter will occur when the conversion rate needs to be changed (due to a change in supply-voltage or load current), since any disturbance (current glitches) to the input- and output ports of the SC-converter must be avoided. Therefore the voltage level on the "flying" capacitors is NOT allowed to change when the converter switches from one conversion ratio to another one. When we regulate the output voltage of the SC-converter by means of a variable internal resistance we have the freedom to choose the conversion phase to be regulated. Doing this we can stabilize the operating voltage on the "flying" capacitors to that value which is the same for both conversion rates N so that when changing the arrangement of the capacitors no additional charge is transferred between the "flying" capacitors and the ports of the converter. It can also be seen that by choosing this "optimum" phase for regulation then in the nonregulated phase the two "flying" caps are always in parallel, so both capacitors are periodically "reset" to the same voltage level even with asymmetric regulation or capacitor mismatch. Another consequence is that a glitch free operation of a "3-gear"-SC-converter cannot be achieved by the regulation of solely one conversion phase. Finally, when the operating voltage on the "flying" capacitors is used as criteria the "ideal" point to change the conversion rate can be detected, since then the resistive losses in the unregulated phase of the conversion cycle are already covered.