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CC2340R2: Questions about LP-EM-CC2340RS schematic

AB Singh
Prodigy 140 points

Part Number: CC2340R2

Tool/software:

Hello TI's Tech Team,

I have a few questions about ur LP-EM-CC2340RS schematic. We are planning to use the CC2340 MCU in few of our new products. I am new to RF design, so please don't mind me asking basic questions.

1) What is the role of C33, C34 and L33? I do understand other passive components.

2) CC2340 has internal 32KHz oscillator as shown in the datasheet (DS) page 3. Also on page 54 of DS, it states the same. But in the EM schematic, why is an external OSC Y1 shown?

3) If we have to use external crystal OSC, is there a part other than the one shown in the BOM? The TZ3359DAAO73 is very expensive.

4) What is the Place Holder for Bead B1? I did not find any description anywhere - even on evaluation board Brief swru588a. We are designing battery powered devices. Do we need this B1?

5) We don't have an SMA antenna in our designs - only have PCB 2.4 GHz trace antenna. Do we need CR10?

So far, these are all the questions.

Thanks.

  • 0
    TI__Mastermind 19835 points

    Hi,

    1) These perform both an impedance matching function for optimum performance of the RF front end as well as a low-pass filtering role for attenuating harmonics to comply with regulatory limits.

    2) Please see desouza's replies in the following thread: https://e2e.ti.com/support/wireless-connectivity/bluetooth-group/bluetooth/f/bluetooth-forum/1350911/cc2340r5-which-applications-use-32k-crystals 

    Although for a different device, some of the (general) details regarding Bluetooth specification's requirements detailed by Ryan Brown1's replies in the following thread are also valid here: https://e2e.ti.com/support/wireless-connectivity/bluetooth-group/bluetooth/f/bluetooth-forum/1237450/cc2652p7-external-slow-clock-requirement-for-cc2652x7-and-ble 

    In short, an external LF crystal oscillator is recommended to meet the Bluetooth specification's requirements.

    3) Please see alternative recommendations in Section 6 of SWRA495 (Crystal Oscillator and Crystal Selection for the CC13xx, CC26xx, and CC23xx Family of Wireless MCUs): https://www.ti.com/lit/swra495

    4) The placeholder is for a ferrite bead (typically BLM18HE152SN1 is used for our Wireless Connectivity reference designs) in case you have a noisy supply and require additional VDDS filtering; it depends on your specific design and if you expect to have other noisy circuitry in your design. For a battery powered application it's not typically required.

    5) CR10 is recommended for ESD protection; it is recommended for both an SMA and PCB antenna if appropriate ESD protection will not be used when handling the unit.

    Regards,

    Zack

  • 0 in reply to ZC
    Prodigy 140 points

    Thanks for all ur replies. I am left with only one further question about CR10. We are using QFN 5x5mm package. Datasheet section 7.2 states that MCU has built in ESD protection of 1000V and 500V respectively. Is that not enough during regular handling of the device? We are trying to reduce the components to save PCB board space and cost.

    Thanks.

  • +1 in reply to AB Singh
    TI__Mastermind 19835 points

    Hi,

    It really depends on how your system unit will be handled (during fabrication/testing/in the field) and whether you anticipate an event that will generate higher voltages than the datasheet specification. That is something you will have to assess.

    One point to note is that if a PCB antenna is used (as in your use case), that reduces the contact a user will have with the RF path to the antenna.

    Regards,
    Zack