Any scheme that increases the impedance from a chip back to the outputs of the power supply is sure to have some tradeoffs. If the MAX232 is in this condition then series impedance in the supply lines will have some effect on the efficiency and ability of the device to recover to transient load changes. Series filtering the device right at its switching frequency starves the device where it needs the lowest impedance.

I would offer up the suggestion that if one is having serious problems with one of the garden variety MAX232 charge pump level translators or other similar chips such as one of the currently popular high voltage LED converters or EL backlight supply devices then a better way to isolate the device than putting series resistors in its supply leads would be to use one of the following two methods.

A) Provide a near by local regulation for the MAX232 with a separate VR than that used for other parts of the circuit board. This separate VR could also be deployed to supply current for LEDs and other similar higher current loads like those I mentioned above.

B) Locate the offending device(s) close to the main VR and then filter the remaining more sensitive devices down wind of the VR through a pi-filter made of a series of appropriately selected multi-layer inductors and low ESR capacitors to GND.

Michael Karas