XTR111: Minimum load resistance

Hi Cedrick,

Our customer wants to know the minimum load resistance that they can use. 

XTR111 is a voltage to current converter or transmitter. Since the output is a constant current source, the load resistance is dependent on the constant source currrent and XTR111's supply voltage. 

For instance, it the circuit is supplying 20mA and max. supply voltage is 24V, then the max. load resistance is approx 24/20mA or 1200 Ohms. Or with 1 kohm resistor as load, the voltage across the resistor will be 20mA*1kohm = 20V. 

Regarding to the minimum load requirements: 

Because the output is constant current source, you may short the output load, if you have to, except you need to make sure that there are no heat dissipation issues at Q1 and 15 ohm etc.. If you short at the Rload in the schematic below, if Iout = 20mA, then the voltage across the 15 ohm resistor is 0.3V, Assume Q1 has  Rdson around 0.1Ohm, its heat dissipation will be 20mA*20mA*0.1ohm = 40 uW, which Q1 will be happy. 

If you have other questions, please let us know. 

Best,

Raymond