AD5412 - DAC current output monitoring

Hi all,

 

I plan to use the AD5412 as configurable current or voltage output interface implicated in a safety function. Because of safety constraints, I have to add a diagnostic to my function in ordre to verify the current/voltage that is actually outputted.

For voltage monitoring, it won’t be an issue.

For current monitoring, I ‘d thought that I could measure the voltage drop across the R3 internal resistor with a differential amplifier.

“Figure 74. IOUT Filter Circuitry” from AD5412 datasheet gives a 40 Ohm typical value. Would it be possible to get the tolerance of its impedance ?

My need doesn’t require an accurate current moniroting (around +/-10% resistor range would probably suit to me); however, I do need a therical tolerance value.

Thank you in advance for your feedback.

 

Best regards,

Jean-Baptiste Osmont

  • 0
    •  Analog Employees 
    on Jun 19, 2017 5:26 AM

    Hi Jean,

    I don't have the tolerance value for R3 right now but I'll look for information regarding the specification.

    If ever we found out that the R3 has a tolerance greater than +/-10%. You could try the following suggestions for your application:

    • If your load is resistive, you can try measuring the voltage across the load to monitor the current.
    • You can also try adding a sense resistance in series with your load, provided that the voltage drop across the sense resistor will not cause the part to hit the compliance voltage at the IOUT pin.

    Best regards,

    Rainier 

  • Hi Rainier,

    Thank you for your feedback, I look forward to get the tolerance values specified.

    Unfortunatly, I don't know  precisly the output load so I can't count on voltage measurement. Indeed, if resistor value wouldn't be accurate enough, worst case would be to add a external series resistor. This said, it would add a voltage drop that wouldn't be entirely compliant with my customer requirements.

    That's why I coun't a lot on R3 voltage drop measurement.

    Best regards,

    Jean-Baptiste

  • 0
    •  Analog Employees 
    on Jun 20, 2017 5:36 AM

    Hi Jean-Baptiste,

    R3 will be close to 40ohms+Rwire, where Rwire is the resistance of the internal metal interconnect on both sides of R3. This internal metal interconnect has a large TC and it varies depending on the current flowing through it. R3 by itself has a +/-10% tolerance but will be affected by the metal interconnect a lot.

    The best option we have to monitor the IOUT is to add a small resistor in series with IOUT to minimize the voltage drop.. The series resistor should have a good TC for a more accurate current measurement at the output.

    Best regards,

    Rainier