Part Number:CC3220SF-LAUNCHXL
Hello,
I'm currently making my way through the PCB design checklist for the CC3220SF and have run into a couple recommendations that I am not sure how to address:
1. For PA DCDC IN (Pin 39), the checklist states that 4.7 uF and 100 uF decoupling capacitors are necessary. However, on the CC3220SF-LAUNCHXL schematic there is only the 4.7uF capacitor, and I'm wondering if the 100 uF cap is necessary or what the reasoning for omitting it on the launchpad is?
2. For the reset (Pin 32) there is an RC circuit recommended by the checklist, and this checklist is reflected by the schematic for the launchpad. However, the resistor in that circuit is only connected to VBAT via jumper J9, and in my testing I've never had that jumper bridged, thus the resistor has no effect on the reset. I have thus omitted that resistor on my board since, but I'm wondering if this is acceptable? I have the reset pin connected to both the UART interface for programming via UNIFLASH and the JTAG header for debugging on my board. Given that there is no resistor in how these connections are wired on the launchpad, I'm assuming this will work similarly.
3. I have both the UART tx and rx connections (Pins 55 and 57, respectively) connected to 100kohm pull ups per the checklist, but these pull ups are not present on the launchpad from what I've seen, is there a reason for this? Is it possible they'll simply be on the debugger?
4. The checklist states that external pull ups are recommended for all GPIO. If a GPIO pin is unused and I have no interest in its behavior, can I simply leave it not connected, or should it still have an external pull up/pull down resistor? Furthermore, the checklist states that the pull ups/downs are necessary to maintain the state of a pin, but how is this possible if the pin is meant to be high before a reset and there is a pull down connected to it?
5. Lastly, I hardwired the SOP headers as such (SOP: 010) to default to the UARTLOAD_FUNCTIONAL_4WJ. According to the documentation for this mode, it should allow me to setup the board via UART after manufacture and load my software into external flash. However, the checklist consistently states that UARTLOAD mode should be used. Has anyone substituted UARTLOAD_FUNCTIONAL_4WJ for UARTLOAD successfully in a similar use case? Are there any unforeseen issues? I'm fairly confident given the documentation but wanted to double check.
I will be using the XDS110 from the CC3220SF-LAUNCHXL to load the software via UART and UNIFLASH onto the custom board. Please let me know if you need me to clarify or provide any further information. Any info is greatly appreciated!