Whether you must connect the one cap to Vcc or can connect it also to GND depends on the charge pump methode used inside.

The following snippet shows the charge pump for the V+ supply inside of a MAX232E:





The charge pumping is done in two steps: First S1 and S3 are closed, which results in a C1 becoming charged by Vcc. Afterwards S1 and S3 are opened and S2 and S4 are closed. So, C1 can charge C3, up to the moment they have the same potential. If you would connect C3 with the "-"-pin to GND, then V+ could never be higher than Vcc! So, you must connect this pin to Vcc!!


But this is not the onle possible way to generate a supply voltage higher than Vcc. You can also use a scheme similar to the following, which I have drawn once for a different thread:




Have a look at the doubler: When the output of TDA2003 is low, the cap connected to its output is charged up by nearly Vin. When the output of TDA2003 goes high afterwards, the "+"-pin of this cap is at about twice Vin. So, the output cap can be charged up to a much higher voltage than Vin.

Take note, you can connect the "-"-pin of output cap also to Vin! There's no need to connect it to GND. So, with this scheme you can connect the output cap either to Vin or to GND.


Kai