External supply of 1.85V

[Jorge]

Hello,

If I supply 1.85V on the "External supply" pins, can i use all the modules of the board (nRF51DK)?

I need to have less than 2V on some of the pins as an output, that's why I'm trying to supply the board with the lowest voltage i can. But it's not working, I tried the blinky project and it didn't work.

Thanks for the help,

Jorge Costa

[MartinBL]

Hi

There are a couple of things that might be wrong.

1. The current from the External supply pins goes through a reverse voltage protection diode:

The diode has a typical forward voltage drop of ~0.32V. So if you hook 1.85V to the external pins the voltage fed to the VDD pins on the NRF51 will be closer to 1.55V. You should measure the voltage on the VDD pins and adjust your power supply to accommodate for the voltage drop. Or you can put a solder drop on solder bridge SB12. Note that if you do this you might break your chip if you accidentally reverse the voltage on the input pins.

2. The LEDs used on the PCA10028 are EL19-21SYGCs. They have a typical forward voltage drop of 2V. Hence if you only supply 1.85V on the GPIO pins they won't light up.

Refer to the nRF51 DK reference files here.

[MartinBL]

Yes they should. Remember that if you have 2V on the GPIOs that is still barely enough to drive some current through the LEDs and their current limiting resistors. Normally, when you power the kit from USB, you will have about 5mA flowing through the LEDs. Maybe you can try the UART example in the SDK for example, to test your chip and get some output from it.