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LTC2983 hard failure causes?


    I'm trying to bring up a new design using an LTC2983. So far I have been unable to get a good reading from the ADC. My fault data is 11000011, which indicates SENSOR HARD FAILURE, ADC HARD FAILURE,  and ADC RANGE ERROR. Unfortunately these error conditions are not well described in the datasheet. 

    I am using C code generated by your application. I have tried measuring a PT100 RTD and a K-type thermocouple.

    I have also tied a channel to ground and tried a single ended read to measure the voltage. 

    Test conditions:

    VDD is 3.3V.

    I measure 2.5V on the VRef pin. 

    I have 10 uF between Q1 and Q2. I have 10 uF between Q3 and ground. 

    VRef_BYP is connected to ground through 10uF and  0.1uF capacitors.

    VRefP is connected to ground through a 0.1 uF capacitor and through 1 ohm resistor and 10uF capacitor.

    LDO is connected to ground through a 10uF capacitor.

    RESETN pulled up to VDD through a 100K resistor.

    There are 0.01uF bypass caps on the eight channels I am using (4-7 and 10-13).

    • Hi, 

         Page 31 of the datasheet describes the fault conditions for an RTD. Each sensor has different conditions, but ADC out-of-range will always be the same at: ADC Absolute Input Voltage Is Beyond ±1.125 • VREF/2 

         Can you send on a schematic?

         If you generated the C-code via the GUI, can you send on the .cfg config file that the GUI can save?

        What is the value of the sense resistor? The errors you describe, if on the RTD channel point to an open circuit or overrange. How is the sense resistor connected to the RTD?