AD8210 Vref1 Current Draw

Hi millsj2 ,

Can you try tying the Vref1 to V+ and connect it to 5V precision supply? I just want to check if the unit is still working since the Vref1 pin shouldn't draw much current.

Also, can you send me your schematic and measurements for better assessment?
Thank you!

Best regards,

Mae

Hi Mae, thanks for the reply.

I'll see if I can tie the supply pins together and see if operation is as expected.

In the meantime, here is what I know:

The reference circuit is a shunt based regulator seen below:

5V0-REF is what I am measuring. It is currently reading 1.4V. VOR is 8V. This tells me there is 3mA of total current through R77 in this scenerio. The LM zener package above requires ~100uA of bias current to regulate to 5V. 

When I depopulate R78, the zener diode produces 5V0 as expected. This means that 3mA of current is being pulled on the 5V0-REF line. The 5V0-REF line is connected to 6 different AD8210's, all with a very similar layout to below:

In this scenerio, the V+ 5V0 rail is 0V as it has not been powered on yet. In reading the datasheet, it states that VREF1 has internal precision resistors to further step down this voltage. I expect that is what the internal draw of this pin is. Can you tell me the total impedance of these resistors, or what the expected current draw of VREF1 is?

Thank you for the help,

Jesse

I should also mention that I have tried modifying the shunt resistor to the 5V0 reference diode to increase the current draw. Current was increased to 8mA with no visible change to the measured voltage (1.4V).

Hi millsj2 ,

Can you try disconnecting the 5V Reference Circuit to the AD8210 first and then measure the output voltage? 

Thank you!

Best regards, 

Mae

Hi Mae,

I cant disconnect the 5V reference, but when I enable the V+ 5V source, the 5V0 reference stops sagging, and the system operates as normal.

This just seems like the ESD diode is clamping the 5V reference to the V+ source. I can update the design for the AD8210 to have its own local reference that comes up with the 5V0 regulator.

Thanks

Jesse