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.
The voltage that your are seeing on the VA pin should be the same with the VOUT pin since VA is the reference voltage to the LDO regulator produced by the GM amplifier. If you're seeing -0.9V on VA, VOUT should also be -0.9V.
Can you please try using higher values for your feedback resistors? Let me know if the problem still exists.Thanks,Alex