How to separate nrf52dk target and probe power bus?

[butch]

On the nrf52dk development kit, I want to power the target nrf52 from an external supply without powering the interface mcu (the debugging probe). How do I wire that? I don't want to measure the current, or debug, I just want to separate the power busses.

My best guess is to 1) turn the "Power" slide switch off 2) cut SB9 and 3) connect my power supply to net Vdd_nRF (on either pin 1 of P20 or pin 1 of P22.) Should that work?

(Fig. 2 "Power Supply Circuitry" for the nrf52DK shows that net Vdd_nRF is connected to net VDD by R6 but looking at the board, R6 is not populated.)

Fig. 2 also shows that SW6 also switches net V5V to net VBUS, but I don't know for sure which of those nets is the power supply to the interface mcu and which is power from the USB cable. Alternatively, if I leave the PowerSwitch in the On position, I could connect my power supply to "External supply" connector P21 if I am then careful to not connect the USB cable? (And the debugger probe would not be powered?)

(A related question is: could I connect DebugOut and DebugIn with a JTAG cable and still use the separately powered debugging probe to flash and debug the separately powered target? I haven't studied that much, but it looks like that is not possible, the cable would be parallel to the hardwired SWD and UART nets between the two.)

[Jørgen Holmefjord]

Hi,

You can download the hardware files for the nRF52-DK here. This includes all schematics for the board. On sheet two of the schematics, you can see that the interface MCU is powered by VDD through SB29. Cutting SB29 will disconnect the interface MCU. You can then power your board through External Supply (P21).

There is no JTAG, but you can connect an external debugger that support the SWD interface to the Debug in port (P18), to flash and debug the nRF52832 IC.

Best regards,

Jørgen

[butch]

Thanks, now I can figure it out.

Here is what I just tested: 1) turn Power switch to off position 2) apply external power to pin Vdd_nRF (do not cut SB9, that doesn't work.) It seems to work (the target flashes the LED's but the interface mcu does not flash its LED.) But I suppose the mcu might still be powered, so I will take your suggestion.

I also would like to suggest an improvement for your next DK: make the target and the interface mcu more easily separable, as on some dev boards for TI MSP430, where there is a clear jumper between the two halves. And I think you can isolate the power supplies but still use the probe half of the board to debug the target half of the board via SWD.