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TIDA-00548: Safety complaint

oM
Intellectual 420 points
Part Number: TIDA-00548
Other Parts Discussed in Thread: ADS1263

Hi,

Iam plan to use TIDA0058 evaluation board based components and schematics for my design. Please clarify below queries


1. The board having SIL3 certification due to the hercules series MCU only? Analog circuit section including ADS1263 have any SIL certification(As because in our design MCU not using, but we need SIL certification)?
2.     a. The evaluation board uses ADS1263 IC for analog input function. The IC datasheet showing the analog input pins are tolerant up to 7V. Then why in evaluation board it is saying 33V tolerant?

        b. By feeding 24V to one end of Rsense pin another end will connect to load. Will this work?

3. whether using ADS1263 can we able to sense current from 0 to 120mA?

Kindly consider this as urgent and reply

Warm regards,

Monisha OM

  • 0
    TI__Intellectual 1270 points

    Hi Monisha,

    1. The board (design) does not have any SIL certification (or any other safety certification). Hercules processors can help to reach certification up to SIL3. Please do not copy this design for your own functional safety application! This article may help you in starting with a FS analog signal chain design.

    2. a) As this is a current only input the voltage is dependent on the shunt resistor R25, diode D2 and input current. With 24.9Ohm resistance and 20mA input the voltage is well below 1.5V. The TVS diode D1 tolerates a steady DC voltage up to 39V at the input. In this case the current would be very high and is limited by the MOSFET Q1. The TVS diode protect the circuit against (very short) surge events. Any steady voltage above 39V may damage the circuit. Please replace 33V by 39V. The voltage drop of the TVS is chosen 39V to tolerate any mis-wiring at the inputs, e.g. 24V PLC power at the input terminals. Note: 33V would also be sufficient, such as TVS3301.

    2. b) This input is designed for sensor transmitter outputs (current loop). The voltage is resulting from the current set by the transmitter and the input circuit of this design as described in 2a. Please do not connect voltage sources to the input - only current sources.

    3. This design supports currents up to 20mA. The architecture allows also higher currents by adapting shunt resistance and/or MOSFET current limiter. Please make also sure all components can handle power dissipation in worst case scenario.

    Hope this helps!

    Best regards,

    Lars

  • 0
    Intellectual 420 points

    Thanks Lars For your reply. 

    3. As per datasheet, minimum loop current is mentioned as 3.6mA. Whether the circuit can measure current from 0mA? Also for to sense 120mA , what will be the sense resistor value?

  • 0 in reply to oM
    TI__Intellectual 1270 points

    Hi Monisha,

    3.6mA is a useful low limit for the 4-20mA loop. 0mA is very hard to detect as one cannot distinguish from broken wire. It may be beneficial to allow a low current (e.g. 100uA) for "0 mA".

    As you read 6x the current the resistance may be 6x lower (4.15Ohm) to have same voltage drop across the shunt. Please also check power dissipation for all components exposed to the higher current. 

    Best regards,
    Lars