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AD7193 NO LOAD 0xFFFFFF

Hello.

The load current is measured by the shunt resistor using AD7193. We observed an AD value of 0xffffff under no load at the site. After that, when a load current of 10A is passed through the returned device, an AD value of about 8A is observed. The calibration was done before shipping, and the correction value in ROM was the same as the value before shipping.

The question is
(1) Is there anything other than out of range or VREF abnormality that becomes 0xffffff?
(2) What are the factors that cause the output to be low for a load of 10A?
VREF is high / low, etc.

Thank you.

Parents
  • I read the data register and status register, confirm that RDY and NOREF are 0, and fetch the data.

  • Hi, 

    Can you probe the actual AIN pins? What's the equivalent voltage? From the schematic you have shunt resistor in 300uohm is that correct? Looking at this it seems that the differential inputs are floating? So without any inputs what's the floating inputs read when you probe it using multimeter? Probe it differentially and each AIN input pins with respect to GNDs. 

    I also noticed a signal name labeled -48V is that an actual negative supply? or is it GND can you confirm this please the part can't accept negative supply. 

    I have contacted the product owner to further assist you on this but if you can provide more details then that would be helpful. 

    Thanks,

    Jellenie

  • Hello

    Thank you for your reply.
    The circuit is actually as shown in the figure below.
    So I tried various things, but I set the offset register to 0 at the time of initial setting, and after about 70 seconds with no load, I read 0xFFFFFF from the data register. The ERR flag is 1. RDY and NOREF remained 0.

    (1) Is there any reason why 0xFFFFFF occurs after a while with no load and does not return to 0?
    (2) Is this ERR flag underranged? Which is the overrange?

    PDF

  • Hi, 

    1. Actually, I am more curious about the -48V. What is the actual potential at that point? Both ADC GNDs are connected to this point. Can you clarify what is the potential voltage at both AIN pins with no load and also the potential voltage with load. If no load means that the inputs are floating then we cannot expect that it should be 0 as the inputs are floating the potential is unknown and can float at any level. There is also an error flagged as you mentioned at point 2 which means there could be an overrange, underrange or invalid reference.  

    2. We do not have specific error flag to determine if it is an overrange or underrange so either of this case will flag the ERR bit. You've mentioned that NOREF bit is not set so this mean that the refence voltage is still valid so we can just narrow down to out of range issue. So like I said might be good to measure both inputs and see if the differential and absolute input voltage range is within the acceptable ADC values. 

    Thanks,

    Jellenie

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