AD8418/AD8206/etc Vref current, noise rejection?

Question

I am considering the AD8418 or similar device for bidirectional current measurement. One option is to connect Vref1 directly to Vs (positive supply) as shown in Figure 1 of the data sheet, but I am concerned about the effect of noise from the supply into Vref. The PSRR for Vs is listed at 80dB min but I assume this does not apply to Vref1. 
 Is there spec similar to PSRR to describe the effect of Vref1 noise on output accuracy? 
 If I connect Vref1 to a voltage reference then I need to know how much current this pin sinks. Is this information available? I assume this current is very low but I would like to be certain. 
 Thanks - Jason

ADIApproved · Accepted Answer

Hello Jason, 
 The internal resistor network of the AD8418 looks like the image below. Any noise at the reference pin will see a 0.5 V/V gain at the output or gain of 1 V/V from both reference pins. The reference pins can sink current base on the resistors in the loop of the ref pin to non-inverting input. Simple computation will be I = (Vref signal)/(75k ohm+1450k ohm + 50k ohm). 
 Regards, 
 Phil