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ADS8344 REF02

Other Parts Discussed in Thread: ADS8344, REF02

Hi,

I my application i need to measure RPM from the pulse meter output 4-20ma. i am using ADS8344 16-bit adc and 250 ohm resistor for converting 4-20ma to 0-5v. I am using REF02,5V voltage reference,IC for ADC Vref. I have problem with ADC reference. 1. REF02 ic is getting heat and burned when i connect the pulse meter to adc input 2. i connected the 5V SMPS directly to ADC Vref pin, now ADC is burnned. i dont know what the problem is please help me to solve this issue.

 

  • Thangadurai,

    It would be helpful if you could send a schematic of what you are trying to do and how you have things hooked up.  It appears that you may have a floating ground when you connect the pulse meter.  All supplies must be referenced to the same ground.  If you have two power supplies and one supply is floating above the other it is possible to exceed the maximum input voltages and the part will burn up.

    Best regards,

    Bob B

  • Hi Bob,

    here is the schematic

     

  • Thangadurai,

    The configuration appears to be ok.  Have you measured the voltage across R3?  There are some pulse meters that have a voltage out option as well as the 4-20mA output.  Are you willing to share any information about the pulse meter itself?  Model number, manufacturer, etc.?

    I believe that there is something wrong with the connection to the pulse meter to the ADC.  It would be a good idea to check everything else first, for example leave the pulse meter off and connect the input to 5V and you should get full scale.  Then try grounding it.  If it appears to work, move on to the pulse meter.  Hook a 250 ohm resistor to the output and measure across the output and verify that it does not eceed 5V.  If this all works, then try reconnecting the pulse meter to the ADC.  You might intially try adding a 33 ohm series resistor at the ADC input so that there is a current limit to the input as a precaution as you reconnect the pulse meter to the ADC.  This should help prevent burning anything up.

    Best regards,

    Bob B

  • Thangadurai,

    One other thing that I was reminded of and neglected to mention in the last post is you have input pins floating on the ADS8344.  Floating input pins can cause device latch-up and overheating of the device.  It is best to to connect all unused inputs to either GND or some other termination voltage up to VREF.  Please terminate the floating inputs before doing any more testing, as this could be the cause of the overheating.

    Best regards,

    Bob B