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REF5050: Voltage output to high

Part Number: REF5050
Other Parts Discussed in Thread: ADS1262, , REF5010

Dear Sirs

My primary 5vdc voltage comes from a USB connection and is therefore unfit to use as a reference voltage for the ADS1262 ADC that I'm using.  I'm using a LTC3221EDC charge pump to get 6vdc to power the REF5050 that I use for the reference for the ADS1262 ADC.  Please see schematic below.  I've looked at the output of the charge pump and it is clean.  I've also looked at the output of the REF5050 and it is clean.  C37 is a 10V Vishay tantalum capacitor with an ESR of 1.8 ohm.  C35 is a 16V AVX tantalum capacitor with an ESR of 1.8 ohm.  Why is the REF5050 output at 5.49vdc?

  • Hi Dennis 

    The output is oscillating. Can you please confirm it on the scope. 

    You are exxeding the output capacitor spec (57pf) and overall ESR. Can you please remove R29 and C37 and check the output. 

    Please refer the layout recommendation given at page 21 of the data sheet.  

     

    Can you please tell what is the ENOB for the ADC you are using?  You can take a look at REF70 which has better noise and temperature drift coefficient compare to REF50 and it is a good fit for high ENOB. 

    Regards

    Trailokya 

  • Dear Trailokya

    I checked the output again with the scope and there is no oscillation.  I removed R29 and C37 and checked again with the scope and there is no oscillation.  The output is still 5.5vdc.  I've used this part before in the same configuration without issue.  I took this old board out (see schematic below) to check the output of the REF5050 and it's right on at 4.998vdc.  

  • Dear Trailokya

    I performed another test thinking the charge pump could be the problem.  I removed R30 and attached a wire to L1 (see schematic below).  I attached a GND wire to system GND.  I then powered the REF5050 with an outside 12vdc.  REF5050 output was still 5.5vdc.  

  • Dennis 

    Thanks for the information. Can you please let me know about further stages.Where is 5V_REF connected in the circuit? Can you please disconnect the ADC/buffer and check it. Also I want to know if you are using 5.5V supply for the further block?

    Regards

    Trailokya 

  • Dear Trailokya

    Please find attached the full schematic of the PCA.  5V_REF connections are marked with red boxes.  I removed BR1 (the pressure sensor bridge).  The bridge is connected to the 5V_REF through the TMUX1111RSVR switch (U4).  The output is still 5.5vdc.  Because there are no passive components between the REF5050 output and the loads, there is no way to disconnect the loads save lifting pin 6 on the REF5050 devise itself.  If I do that, it will disconnect the output from the output filter.  Will this be a problem?  

    10mm_Top-Hat_Constant_Voltage sch rev 1 6-14-2022.pdf

  • Hi Dennis 

    • If you diconnet the output with from the capacitor , it won't work. 
    • Can you please remove the REF50 pin 6 and and check what is the output you are getting across C35. I suspect it is getting shorted from some where else on the board. 
    • The drop out of the device is 200mV in unloaded condition and 750mV in loaded condition. Can you please check the output volatge at VIN = 5.75 , Vin = 5.5 and Vin =5.25V .

    Also can you please conifrm if you are seeing this issue at multiple parts. 

    Regards

    Trailokya 

  • Dear Trailokya

    If you diconnet the output with from the capacitor , it won't work. 

    I think I'll try to connect a capacitor to the lifted pin 6 to see if this make any difference.  

    Can you please remove the REF50 pin 6 and and check what is the output you are getting across C35. I suspect it is getting shorted from some where else on the board. 

    I'll do the experiment and let you know what I find.  

    Also can you please conifrm if you are seeing this issue at multiple parts.

    The condition is on all PCAs that I've tested.

  • Thanks Denis. 

    Please vary the supply also and check , you can do this experiment in last if you are sure that 5.5 is coming from REF only.  

    Regards

    Trailokya

  • Dear Trailokya

    As I mentioned above, I connected a capacitor to the lifted pin 6 and powered the REF5050 with 12vdc.  The output voltage was 10vdc.  I'm embarrassed to say that the REF5050 is a REF5010.  I don't know how this happened but that's the problem.  I apologize for wasting your time.  

  • No problem , glad you figured it out.

    Good luck with your design

    Regards

    Trailokya