• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 38 subscribers
  • Views 830 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TIDA-01228: TIDA-01228 : FET switches

Jacques MACE
Prodigy 10 points
Part Number: TIDA-01228
Other Parts Discussed in Thread: CC1310, CC1312R, TIDA-010050

Hello,

I am planning to build LC-sensor based water meter so I started studying the reference designs.

I now understand how a LC-sensor works, however I am having issues understanding something in the TIDA-01228 circuit.

It is stated in page n°5 of TIDUD25A (https://www.ti.com/lit/pdf/tidud25) that FET are used as simple current switches to charge the LC-tanks. 

I don’t get why the design doesn’t just use a GPIO as an output as they should be able to source enough current (maybe that is where I’m wrong ?) 

I also saw in SLA578 that LC tanks are directly excited by the GPIO of the MSP430DW42x. 

Could someone please explain why FET switches are used in this particular case ? 

  • +1
    TI__Intellectual 1895 points

    Hello Jacques,

    I think you refer to SLAA578.pdf here: MSP430FW42x ScanIF Demo Box Hardware/Software Description

    Note that the MSP430FW42x devices contain a dedicated peripheral module, called SCAN Interface for Rotation detection (hence the letter W for Water meters).

    This SCAN module has a state machine (and other blocks) and does generate a VCC/2 voltage with a dedicated buffer output, which is output to the LC-tank. The input signals are High-Z or GND, such that the Oscillation happens (see Datasheet and Rotation Detection With the MSP430 Scan Interface (Rev. B).

    On CC1310 and the next generation device CC1312R data sheet, product information and support | TI.com we do not have SCAN module nor VCC/2 voltage generation circuitry, so we designed the TIDA-01228 reference design | TI.com circuitry.

    We utilized the Sensor Controller Engine (SCE module) for that function. Note that we also have improved the TIDA-01228 solution in TIDA-010050 reference design | TI.com, where we used the DAC and 2MHz mode of the CC1312R to count the oscillations (no TDC module needed).

    TIDA-010050 itself is building upon the BOOSTXL-ULPSENSE Development kit | TI.com but we added some changes to improve the performance, such as GND-ing the unused Inductor, while the other LC-tank is oscillating.

    In summary, you may choose between TIDA-01228 and TIDA-010050 reference designs (lower-power, due to the higher performance CC1312 device and improved SCE module).

    We have done lots of SPICE simulations of the LC-tank circuitry and the only solution for CC13xx devices we found is using FETs on CC13xx.

  • 0 in reply to Milen
    Prodigy 10 points

    Hello Milen, 

    Thanks for the clarifications, it really helped me understand what was going on with these designs. I didn’t know TIDA-010050 existed. 

    I think I might upgrade to CC1312R considering its low-power capabilities compared to the CC1310. 

    When reading Design guide — TIDA-010050, I got interested in running the simulations by myself on SIMetrix/SIMPLIS, as it is stated a LC-sensor model is provided (p.8 part 3.1 Hardware Design). However I can’t find it anywhere on the design files (I'm not sure if this is normal or not). I'll just copy the circuit from the screenshots.

    Anyway thanks a lot for helping I think it resolved my issues for now. 

  • +1 in reply to Jacques MACE
    TI__Intellectual 1895 points

    Hello Jacques,

    I'm glad that my clarifications helped you further! Attached are the Simulation files for TIDA-010050, hope that will save you some time!TIDA-010050 Simulation.zip

    Regards,

    Milen