Is it possible to disable 5V input pin temporarily?

[Nerdwolf]

Hi all,

For my project I power the nRF51 DK from a supercap using an external LDO(3.3V) connected to VDD. This way I can keep the board powered using the supercap. I also provided a pcb trace directly from the output of my supercap(max supercap charge 5V) towards the 5V input.

Now my question: Since the output of the supercap is both connected to the 5V pin(directly) and the VDD pin(using the external LDO) my nRF51 consumes too much current. When I detach the 5V pin current consumtion is much lower since only the external LDO is used.

The only reason why I need this direct 5V->Supercap connection is to charge my supercap again when the nRF51 DK is connected with USB. This works, but the exessive current consumption bothers me.

My Question: Is it possible to completely disable the 5V pin( something like high impedance+-) and only connect it when a USB cable is connected?

Thanks alot!

[RK]

You can't disconnect or hi impedance the 5V pin on the chip. Can't you use a diode or similar to stop the supercap discharging back through the 5V pin and only let it charge up when 5V is connected?

One way or another if you want to do this you'll need some external circuitry to do what you want, there's nothing on-chip (that I can think of).

I hope I understood your setup properly.

[Nerdwolf]

Diode might be indeed the best option to prevent undesirable discharging. I just thought there might have been some on-chip solution for this because I already made the pcb's :)

[Hung Bui]

@Nerdwolf: Have you shorted the solder bridge SB12 ? There actually an diode on the External supply port (P21) however it's not on the direction of your use :).

I guess adding an external diode is a good choice here. In addition, a battery charger IC should be considered.