3 Replies Latest reply on Sep 18, 2019 11:03 PM by BoonT_56

    CYW20719 Programming and Boot Issue




      I am using a CYW20719 MCU in a custom design, most of my design is based on the CYW920719Q40EVB reference design. I have attached my schematic below. I am programming the device using a 3.3V FTDI USB-to-UART cable, which I have successfully done before on the development kit attaching it to the serial jumpers.




      First, I have probed each test point pictured and verified that they behave as expected. The internal buck converter and voltage regulator is operating correctly, and the reset circuit operates as expected. The RESET and RECOVER buttons (not pictured) connect the RST_N or BT_UART_CTS nets, respectively, to ground. After powering up the device, I have verified with an oscilloscope that the 24.000 MHz oscillator waveform is good. The 32.768 kHz oscillator does not oscillate in the default (unprogrammed) state, it appears.



      This is the antenna circuit being used, utilizing the Johanson Technologies 2450AT42B100E, which I have used successfully before with the CYW20719, following all of the appropriate design guidelines.


      My problem is:

      The device will not program, I have swapped out several components including the CYW20719 itself, on each iteration, all operating parameters seem fine (CBUCK voltage, oscillators, etc.). One strange behavior (which I have not verified if the development kit also behaves this way), is that the 24.000 MHz waveform nearly doubles in amplitude and looks distorted (but is still on frequency and roughly sinusoidal), only when the device is put into RECOVER mode, but will return to normal (1.0 Vpk-pk) when reset into non-RECOVER mode. I had a device program once randomly (without changing anything from before when it would not program) and then never again. I have since swapped out the chip and have not been able to see any successful programming again. Are there any obvious errors or concerns with my design? Or any tips or things I should check for?



        • 1. Re: CYW20719 Programming and Boot Issue

          There are actually some requirement on the 24MHz crystal. You may check it out in the datasheet and ensure that your crystal satisfied them.

          I also assumed that your voltage detector circuit does indeed give you a delay of more than 50ms.


          The key thing is that the device must be woken up into the HCI mode, and this is done by shorting BT_UART_CTS_N while powering up.


          Putting 2073x, 2070x, and 20719 Based Devices or Modules in HCI Mode – KBA225450


          Can you relax your load capacitors (C11 and C12) to 10pF and observe whether the situation improve?

          • 2. Re: CYW20719 Programming and Boot Issue

            I have verified that the voltage detector circuit delays enabling the device by more than 50 ms and the issue persists. The crystal I am using is https://ecsxtal.com/store/pdf/ECX-2236.pdf. (24MHz ±15ppm Crystal 8pF 60 Ohms 4-SMD, No Lead )



            I also replaced C11 and C12 with 10pF capacitors. The waveform is shown below:


            • 3. Re: CYW20719 Programming and Boot Issue

              For chip-on-board design, it's inevitable that you will have to perform some tuning on the crystal. I can suggest the following:

              1) swap another crystal

              2) change the load capacitors to 12pF/15pF and observe

              3) employ unequal load capacitors. You reported above that the amplitude of the waveform was high during start-up, then you may increase the loading capacitor on the Input port to say 12pF and maintain 10pF for the other one.


              For the record, our reference design used TXC 8Y24070015 for the 24MHz crystal with 12pF as the external loading capacitors.


              Taking a step back, you have apparently built a PCB board and doing some testing, our discussion may be limited to component changes

              on the schematic. However I know that issues arose out of less than ideal layout and placement are a different ball game altogether.


              Chip on board designs are beyond the scope of this forum. If you still encounter issues, please log in a case at the Cypress URL.

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