ADG1409 for switching power supply. Drop voltage

Hi all,

I have a problem with this circuit. I'm using this circuit to mux two power supplies (+5V or +12V) to 4 different outputs (+EXC1, ..., 4).

To generate +12V I'm using a Step Up. This step up generate +12V @ 30mA and it is limited to a 40mA max.

To simulate a variable load, I've connected an adjustable resistance from 200 to 1kohms.

When the Radjust is 1KOhm the current through it (and S1A of U10) is about 12mA and voltage at pin S1A of U10 (+EXC1) is 11.5V.

But when the Radjust is 400ohm (max desired current of 30mA through Radj), the voltage at the same pin is only +8.5V. The output of Step Up is +12V. So,

1. That mean that Ron (of both MUX) increase when the current, through analog switch, increase? this information isn't in the datasheet. For ADG1409 the max continous current in S,D switch is 120mA at +25ºC.

Can anybody help me please?