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ADS131M04: ADC output data read abnormal when input slightly over scale

Part Number: ADS131M04
Other Parts Discussed in Thread: ADS131M02, OP07,

Tool/software:

Hi Team,

My customers are using ADS131M04 and facing a problem. When they manually increase the input voltage slightly over 1.2V and reach around 1.37V to 1.45V, the data output of M04 is not 7FFFFFh meaning that the input might be over input range. Instead, they read a 0.99V from the output data, which seems quite strange. But when they decreased the input voltage below 1.2V then the data is back to normal and correct input voltage can be read. 

The schematic is as below, could you pls help giving some suggestions on why the data read is clamped at around 0.99V when input over the range. 

BR,

Manu

  • Hi Manu Chang,

    Can you please help us track this opportunity by providing the customer name in the Notes section of the Thread Tracking Toolkit?

    -Bryan

  • Hi Bryan, 

    Have already submit the customers name in the Notes. Pls help with this question, thanks. 

  • Hi Manu Chang,

    Thanks for providing the info. Our apps support for the ADS131M04 is out of the office today, we will respond to you on Monday

    -Bryan

  • Hi Manu,

    Thank you for your patience. I have seen your email about ADS131M02 in the same customer, are these ADCs used in different projects in this customer?

    Regarding this query, can you please confirm if the input voltage signal was connected to S2 test point or pin 2 of U22(OP07) ? if possible, please upload the schematic of the feedback loop of U22? 1.37V~1.45V input has exceeded the recommended operating conditions as shown in the table 6.3? Why does the customer care about it?

    BR,

    Dale

  • Hi Dale,

    Thanks for your response. Yes, there are questions from different projects of same customer. Pls check the OP07 part schematic as below. The input voltage is the S2 test point. 

    Customers concern is that when the input voltage range is over scale, the code received should be always 7FFFFF so that the MCU can recognize and change the scale to different gear. However now when the input is over scale, the data read is only about 0.99V, so they cannot recognize the over scale issue.  

    BR,

    Manu

  • Hi Manu,

    I tested 1.1V/1.2V/1.3V and 1.4V input voltage on ADS131M04EVM board, the code from ADS131M04 ADC is always 8388607 (0x7FFFFF) when the input voltage is higher than 1.2V. Please see the attached data file. I did not see the phenomenon the customer reported.

    Please ask the customer to remove R40 resistor which can avoid any impact from the amplifier circuit, apply DC signals to S2 test point to check again.

    The schematic of the M04 ADC looks good to me, but please ask the customer to remove the inductor L5 and directly short AGND and GND. The inductor L2 between AVDD and DVDD may not cause a problem but inductors are not recommended for precision ADC circuit.
    ADS131M04EVM_20240618.zip

    BR,

    Dale