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TLIN1431-Q1: Watchdog safe trigger area calculation for Pin mode control

Sri Viswa Sathiamoorthy
Prodigy 225 points

Part Number: TLIN1431-Q1

Hi,

In pg no:43, I could find the reference calculation for calculating safe trigger area of watchdog service.

I have performed the same calculation and I like to know if it is correct i.e it considers all worst case scenarios and I haven't left anything.

In pin mode control, we are connecting it to GND and hence the total window size configured (Closed+open) is 32ms to 48ms.

1)In pg no: 43, 10% oscillator tolerance is considered. Whether 32ms to 48ms already considers this tolerance (or) do we need to add separately i.e 32ms becomes 28.8ms and 48ms becomes  52.8ms so that total window size becomes 28.8ms to 52.8ms?

2)Based on the consideration that 10% tolerance is already captured in 32ms to 48ms, I have estimated that worst case safe trigger area as 8ms & we have to service our watchdog every 28ms ± 4ms. Is that correct? (attached image for your reference)

image.png

Thanks,

Sri Viswa

  • 0
    TI__Guru 67097 points

    Hi Sri,

    1. Please note that page 43 mentions the 10 % is included. Hence, you do not need to include an additional 10 %.

    2. Please note that the min total window for 32 ms implies servicing 28ms ± 4ms is risky as it leaves no margin for unexpected delays. You may service 24 ms nominal ± 2ms margin I..e earliest 22 ms and latest 26 ms as this should give a 6 ms margin below the 32 ms min, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 225 points

    Hi Michael,

    1. Thanks.

    2)Regarding 24ms ± 2ms i.e earliest 22ms and latest 26ms: 22ms falls under closed window when total window max is 48ms (image below). Similarly 24ms is at the margin of closed window.

    I suppose, we have to take 28ms ± 2ms i.e earliest 26 ms and latest 30 ms and we will also have 2ms margin on both sides. 

    Kindly confirm if 28ms ± 2ms is correct? (or) please correct me

     

    Thanks,

    Sri Viswa

  • 0 in reply to Sri Viswa Sathiamoorthy
    TI__Guru 67097 points

    Hi Sri,

    Yes, 28ms ± 2ms is a safe choice as I presume 2 ms is included as a safe margin for the MCU jitter and all other delays, thanks.

    Best Regards,

    Michael.