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]

1. Yes, radio == nrf52832. 2) It doesn't matter what the original purpose is, if the pin VDD_NRF of the board is on the net that includes the pin VDD of the nrf52, then it can be used to power the nrf52. 3) whether the LED's draw current depends on whether the app turns them on, so they they COULD be powered from VDD_NRF without much affecting measured current of the nrf52 itself. And the DK could just as well have solder bridges for the LEDs to choose their power supply? 4) The reason I want to isolate the nrf52 power is that I am testing an ultra-low, solar, power supply ranging from 1.8 to 2.4 volts typical in low light of 200lux, with the app duty-cycling the radio, and I don't want any other chips draining power. Its not a big deal, I am not trying to be critical, I very much like the product and the open communication, thanks for your informative and helpful response.