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CC2650: Schematic review - RF frontend

Giacomo Zanichelli
Intellectual 445 points
Part Number: CC2650
Other Parts Discussed in Thread: BLE-STACK

Hi there, I am a EE graduate student. I am designing a custom board using the CC2650. I have completed the schematic and the pcb design and I would like a review of my schematic and gerbers just to make sure I did everything right. This is indeed the first time I design a board. In particular, the RF part is what worries me more. The TA who followed me in the design recommended this scheme and routing but, according to the TRM and  what I've done appears to be different (with single-ended antenna, is it correct to short circuit RF_N and RF_P if I remove the inductance?).

Thank you in advance for your time,

Jackmicrocontroller_schematic.pdfbattery_management_schematic.pdfsensors_schematic.pdfpower_schematic.pdf

  • 0
    TI__Genius 11810 points

    Hello Giacomo,

    • Do not short circuit the RF_N pin to RF_N. For single ended operation either leave RF_N floating, or connect a 15 nH inductor between RF_N and RF_P for external biasing.
    • C10 and C11 can be set to DNM. CC2650 has internal decoupling capacitors for the 24 MHz crystal. 
    • We do not recommend routing traces under the exposed pad.
    • Add gnd plane to top layer.
    • Place matching components L1, C4 and C5 closer to CC2650.
    • Try to follow our reference design for 2 layer boards. PDF-file is included in the .zip-file found here: http://www.ti.com/tool/cc2650em-4xs-rd 

    Best regards,
    Simon

  • 0 in reply to Simon J
    Intellectual 445 points
    Thank you Simon for your quick reply.

    I am also writing the firmware and would like to use the same 2 pins to program the board (cJTAG with TCKC and TMSC) using the XDS110 debugger of the CC2650 Launchpad and to debug using UART. Is it possible to remap programmatically TCKC and TMSC in order to forward UART data after programming? I would like to reduce as much as possible the size of the connector on the board (the Launchpad has an 11 pin connector with jumpers I believe). Which is the minimum number of pins required to be able to debug my application on the custom board?

    Best regards,
    Jack
  • 0 in reply to Giacomo Zanichelli
    TI__Genius 11810 points

    Hi Jack,

    No, the TCKC and TMSC pins cannot be programmed to any other peripherals. To debug your board you will need TCKC, TMSC, RESET and power. 

    Best regards,
    Simon

  • 0 in reply to Simon J
    Intellectual 445 points

    Hi Simon,

    I followed your advices (I couldn't move the matching components closer to CC2650) but I cannot get the Bluetooth to work. I've also followed the CC26xx_HW_Troubleshooting guide:

    • I'm using cJTAG with XDS110
    • Do I need to change something to use internal regulator mode? It seems the default mode
    • voltages and current draw seem to be correct
    • the I tried to follow the software bring up procedure. However :
      • "initial-board-bring-up" guide is related to the BLE-Stack 3. I'm using the BLE-Stack 2 with CC2650. Is there something I should take care of or are the 2 procedures compatible?
    • I tested the board with Simple Peripheral application, with the following modifications:
      • set the RF to SE and the biasing to INTERNAL
      • removed all GPIO from the gPIOiNITtABLE, leaving only PIN_TERMINATE

    After all that, the Bluetooth does not work, I cannot even see it using a smartphone application. Is there something I can do to exclude hardware issues? What should I see on the input of the antenna, for example? and on RF_P pin? 

    In parallel, I've also tried to create a custom board file. I followed the guide for BLE-Stack 3 but I couldn't get it to compile, I think the folder structure is different and I couldn't identify the errors.

    Best Regards, 

    Jack

  • 0 in reply to Giacomo Zanichelli
    Intellectual 445 points
    Hi Simon,
    I would much appreciate a feedback from you.

    Moreover, I am trying to debug my custom board over the 2 cJTAG pins using XDS110 of the Launchpad. I tried to printf something on the console (by including <stdio.h>) without success. I was able to do the same with Launchpad: I tried to remove all jumpers except TMSC, TCKC, VDD and GND and I am able to see the printf on the console. Do you have any idea of what the problem might be?

    Best regards,
    Jack
  • 0 in reply to Giacomo Zanichelli
    TI__Genius 11810 points
    Hi Jack,

    Have you tried running and debugging a simpler project like one of the rtos driver projects?

    Have you selected the correct RF pin (RFP) for single ended RF front-end?

    Best regards,
    Simon