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AD8210 Vref1 Current Draw

Category: Hardware
Product Number: AD8210

Hello,

I am using a 5V precision reference to generate Vref1 on the AD8210. V+ is generated using a nominal 5V0 non-precision supply. Vref2 is grounded.

In this config, my precision reference is being pulled low to ~1.4V, like too much current is being drawn from the reference. I have not found information in the datasheet yet regarding what kind of current draw I can expect from Vref1. 

What kind of nominal draw does Vref1 have? If V+ is unpowered and at 0V, but Vref1 is at 5V, does that affect current draw into Vref1 at all? If it is in the datasheet and I missed it, please let me know. 

Thanks

Jesse

  • Hi  ,

    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  ,

    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

  • That's good to hear. If there are still issues that comes up, feel free to ask again. Thanks!