Hi
I'm working on a new project using the nRF9151 SMA DK and I have some questions that I haven't been able to answer by searching this forum or reading through the documentation.
1. The hardware guide says the board should be powered from either USB or the VIN pin (pin 9 on P20). However it would be advantageous for my project if I could instead create a shield during prototyping that supplies 5v via pin 5 of P1. SB35 (closed by default) connects the P1/P3/P7 5V pins to VDD_5V, so electrically they appear to be the same net as VIN_5V on P20. Is this a supported way to power the DK, or are there caveats I should be aware of (e.g. the power switch SW6, power-input selection FETs, etc.)?
2. The guide says only one source should be applied at a time but doesn't say why. My assumption is that it's to prevent reverse current flow between the two sources. For my application I'd like the DK to remain powered from the vehicle's 12 V (via a buck) while also being able to connect USB for programming/debugging, without having to disconnect either side. I'm planning to put a Schottky in series with my buck output (cathode toward the DK's 5V net) to prevent USB current from flowing back into my buck. Looking at the power input section of the schematic, it appears that Q9 (MCM2301-TP) provides similar reverse-blocking on the VIN_5V -> VBUS path via its body diode. Is that the intended behaviour, and if so, would my Schottky + the existing Q9 be sufficient to safely connect both sources simultaneously? Are there any other failure modes (transient behaviour during USB plug-in, SW6 interaction, USB_DETECT logic, etc.) I should be aware of?
Thanks,
Mark