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Original question:

CC2640R2F: the MCU not working

CC2640R2F: MCU not working, DCDC is down

Angel Ros
Prodigy 50 points
Part Number: CC2640R2F


Hi, on a custom PCB the MCU is not working. I found that on the DCDC_SW I don't have the signal of the DCDC and even when i reset the MCU, I don´t make the DCDC restart. 

I have the MCU configured to use de internal DCDC and to use the internal oscillator (32kHz clock) and for the HW i have an inductor and a decoupling capacitor (with a short ground path)

How can i recover the MCU? There is any way to make it work?

Thanks

  • 0
    TI__Guru** 106705 points

    Hi Angel,

    Are you able to detect your board from Flash Programmer 2? Are you able to control the radio from SmartRF Studio? Which SDK example have you been using so far?

    Can you share a snippet of your schematic and layout encompassing the CC2640R2F and all required passive components?

    Regards,
    Fredrik

  • 0 in reply to Fredrik K
    Prodigy 50 points

    No, I can´t detect the MCU and i can´t see anything through the radio.

    Regards

  • 0 in reply to Angel Ros
    Prodigy 50 points

    I have more devices with the same HW (and the same FW) working and i can see the DCDC signal on the DCDC_SW pin (on the working devices), but some of them (from the same production line) doesn't work. We can't see the DCDC signal and the device doesn't respond even when we restart it or switch it off.

    Regards

  • 0 in reply to Angel Ros
    TI__Guru** 106705 points

    Hi Angel,

    The inductor in the schematic says "ferrite bead". It should be a 10 uH chip inductor. The capacitors are also missing values, are these correct?

    Can you share more of the schematic and layout as requested earlier?

    Regards,
    Fredrik 

  • 0 in reply to Fredrik K
    Prodigy 50 points

    hi, 

    yes L1 is an inductor of this value and the values of C6, C7 and C8 are of 10uF, 01uF and 0.1uF respectively

    Regards 

  • 0 in reply to Fredrik K
    TI__Guru** 106705 points

    Hi Angel,

    I looked at the layout you sent me. It is deviating significantly from the reference designs. As clearly noted in the reference design schematic, and as is common for all switching regulators, the DCDC inductor and capacitor must be placed close to the DCDC-SW pin. 

    From what little I can see, there are also other issues with you layout, ground plane, decoupling component placement, etc. I would recommend you to go through the design guidelines found here:  

    Regards,
    Fredrik

  • 0 in reply to Fredrik K
    Prodigy 50 points

    Thank you Fredrik! we will check it and modify it.

    On the other hand, it can be affected by the approach of a magnet? on the production line we use a magnet that activates a sensor and it passes close to the DCDC area.

    Best regards

  • 0 in reply to Angel Ros
    TI__Guru** 106705 points

    A magnet will definitely affect the inductor and thus the DCDC operation. This can very well be part of your problem.