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ADS1230 connection to Load Cell

Kavitha Narayanaswamy
Prodigy 110 points
Other Parts Discussed in Thread: ADS1230

On Fig 33 of AD1230 data sheet the load cell is directly connected to the Pin No 7 and 8 of the IC. Is it recommended to connect a Series Resistor of 100 Ohms in between the Load cell and Pin Nos 7 and 8 respectively and also add a 0.1uF Poly Cap between 7 and 8 and another 2 Nos. to connect 7 to GND and 8 to GND. Kindly advise. We are facing problems and the  ADS1230 data is latched in between during a periodic weighing scale measurement.. When we try to measure the voltage across Pin No.7 and 8 using Multimeter then the ADS1230 shows the normal voltage and is released from this latch. The latch generally occurs at 6 to 7 mV. The weighing scale is subjected to an increasing ramp of 2mV to 8mV periodically every 14sec. After 2 to 5 Hours we see that the ADS1230 output as read by the controller is latched up at 7 mV whereas the actual load on the loadcell is around 2mV. When we try to measure the ADS1230 goesback to 2mV. This is a board supplied with a LoadCell vendor and the circuit has three 0.1uF capacitors one between 7 and 8 and another between 7 and GND and also between 8 and GND. There is also a 100 Ohm resistor in between the load cell to ADS1230 on pins 7 and 8 respectively.

  • 0
    TI__Guru** 113765 points

    Hi Kavitha,

    Generally the load cell is resistive and adds series resistance in addition to the series 100 ohm resistors.  So it is not a problem to add the series resistance and the filter caps.  However to limit drift issues we do recommend making the common-mode capacitors to at least 1/10th the value of the differential cap.

    I think a better term for your condition is stuck as opposed to 'latched up'. A latch up condition usually requires a power down restart to work again.  If the value being returned by the micro is exactly the same each time, then you will need to do some more investigating of the communication.

    Is the micro on the same board as the ADS1230?  Perhaps you have a communication or wiring issue?  How is power being applied to the ADS1230?  And is the ADS1230 supply the same for excitation of the load cell?  Is DVDD and AVDD the same voltage?  Is the AGND and DGND connected directly together?  How is the PDWN pin of the ADS1230 being controlled?  A schematic would also be helpful. 

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 110 points

    Yes the micro controller is on the same board. The connection schematic is attached. That would answer all the questions. Pls let us know if we need any modifications to be done.

  • 0 in reply to Kavitha Narayanaswamy
    TI__Guru** 113765 points

    Hi Kavitha,

    Unfortunately the schematic did not get attached.  When replying use the 'rich text' reply option, then select the 'paper clip' icon to attach the file.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 110 points

    I am not getting the Rich Text Format option from  . the menu I think it is already enabled. I used the paper clip to attach the schematic again now.  Pls check again if it is attached. Or I will try to send you a google link for the same.

  • 0 in reply to Kavitha Narayanaswamy
    TI__Guru** 113765 points

    Hi Kavitha,

    As I mentioned before the common-mode caps should be smaller than the differential cap.  There should be bypass capacitors (0.1uF) at each of the supply connections to the ADS1230.  As I cannot see how the micro supply is connected, there should also be a bypass capacitor at the micro VCC supply input as well.  I would also suggest a capacitor across the reference inputs as well. 

    It is not shown how the 5V is supplied or established.  It may be possible that some interference on the 5V supply could cause an issue with transients.  As I cannot see the PCB layout, I can only make a couple of suggestions.  Make sure that the analog signals do not cross paths with the digital, and make sure you have a ground plane as opposed to just ground traces running from point to point.

    Best regards,

    Bob B