What is the voltage level of the external power supply you are using? The FP-AO-200 and cFP-AO-200 output load drive capability is based upon the voltage of the external supply that you are using. They each have an internal 3 volt drop. You can use V=I*R to determine the load drive capability. For example, with a 5 volt external supply, you have the 3 volt drop, so 2 Volts/ 21 mA = 95 Ohm load maximum. With a 24 V supply, you can drive the maximum rated load of 1000 Ohms. For a 350 Ohm load, you will need a minimum of a 10.5 Volt supply.