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TIDA-01599: Question on Component usage

Part Number: TIDA-01599
Other Parts Discussed in Thread: ISO1211


trying to understand the reason for using U2 (SN74LVC2G132YZPR) dual NAND gates instead of a single AND gate? what is the advantage of inverting the signal and using this dual NAND part?

also, i assume the dual R6 and R13 resistors is for HFT=1? if this is the case, why wouldnt you have dual R16's resistors in parallel in case of open circuit failure in the R16?

  • Hello Ben,

            Thanks for reaching out. Please find my answers as below:

    • NAND gate: The previous version of design was using one package AND gate for dual safety channels. In order to achieve HFT=1, we separated with two logic gates. Since we tried to do less modification on the layout, dual gates were implemented. Of course you can use single AND gate.
    • R6 & R13: Using 2 * 499 ohm resistors is to reduced the possibility of resistor failure mode " short " and " change value " which will impact the filter cut off frequency. The safe MCU will send 1ms diagnostic pulse periodically to detect the ISO1211 condition and the RC will help to filter these pulse to ensure the drive normal operation robustness.
    • R16: the "open" failure of R16 belongs to "no effect faults" from the safety perspective. So additional resistor in parallel will not help to improve either for the diagnostic coverage or for the system robustness.