ADP7183 Adjustable Voltage

I am using the ADP7183 in adjustable mode to achieve the DC voltage of -0.9V.

Following the formular in the datasheet, the output voltage is given as V=-0.5(1+R1/R2).

We set R1=8k Ohms and R2=10k Ohms.  Under such a setting, the adjustable output voltage is supposed to give V=-0.9 V.

However, in our test, we measured the output voltage as V=-1.5V in such a setting.

We also measured the voltage at the Low noise reference voltage pad VA is -0.9 V. 

We tried all possible ways to obtain the -0.9V in this way but still it is not successful. 

Strangely, we have another ADP7183 using a similar setting but only replacing R1=4k. It ouputs R=-0.5(1+R1/R2)-0.5(1+4k/10k)=-0.7V.

We are very grateful if you could help any suggeustions what is the cause of the problem.