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PGA450Q1EVM: Latency between echo received and fifo, fifo to LIN and typrical time between bursts when fifo will be updated with new data

Ronda Collier
Prodigy 10 points
Part Number: PGA450Q1EVM
Other Parts Discussed in Thread: TUSS4470, PGA450-Q1, PGA460

Hi there!

I am working on a design to detect an approaching object and then to generate an alert when an approaching object is detected.

I am trying to compute the latency. To do this I need:

-An approximate number of clocks (assuming 16MHz) to get through the datapath and into the fifo. I understand this will depend on the configuration so typical would be good.

- Time in clocks from fifo to LIN bus

- Typical time between fifo updates. Also understand this depends on burst config though typical would help.

We are doing back of the napkin calculations to determine the latency between detecting an object approaching from max distance and being able to generate a local alert.

Thank you so much!

Ronda

  • 0
    TI__Mastermind 27950 points

    Hi Ronda,

    The latency between measurements is primarily dependent on the maximum distance you need to detect. Assuming you are making an ultrasonic time of flight measurement through air, this will be on the order of milliseconds. The equation to determine the round trip time of flight based on a maximum distance and known speed of sound can be calculated as:

    round_trip_TOF (s) = (max_distance_one_way (m) * 2)  / velocity_of_sound (m/s)


    For example, if my maximum required distance through air at room temperature is 5m, then:

    round_trip_TOF = (5m * 2) / 343m/s = 29.2 ms

    The FIFO fills real time during the record cycle through the round_trip_TOF iteration.

    The time for interface-communication is negligible compared to the actual TOF measurement. Assuming a LIN bus operating at 19.2kBaud, each bit is 52us wide. Depending on the post TOF processing functions and amount of data sent over the LIN bus, you can assume an additional <4m.

    By the way, the PGA450-Q1 is very old, and we have released several newer and better performing devices, such as the PGA460 and TUSS4470. Check out the Ultrasonic E2E FAQ for more details on specific part recommendations based on your application type: https://e2e.ti.com/support/sensors/f/1023/t/748143