floating reset pin

RE: floating reset pin

MartinBL — Thu, 12 Jul 2018 10:50:35 GMT

Hi,

I don't think those trace lengths are anything to worry about in itself, but everything is relative. Can you upload your schematic and layout files (preferably in Altium or Gerber format).

Do you have more reasons to believe that the reset pin is at fault other than the current consumption?

What kind of application are we talking about?

If the device is resetting I assume the customer would notice in more ways than just higher current consumption?

5mA could indicate several things. E.g.

A bug in the firmware prohibits the CPU to enter sleep mode.
The radio is transmitting a lot.

Is it possible to get some logging data out of the device for debug purposes? It could be very interesting to see what the application is doing, and it would be quite easy to see if the device resets.

RE: floating reset pin

roger.k — Thu, 12 Jul 2018 05:17:29 GMT

Thank you very much for your help.

1. Reset, SWDIO, SWCLK signals have no connection. And PCB line lengths are as below.

1.1 Reset : 36.35mm

1.2 SWDIO : 42.53mm

1.3 SWCLK : 31.86mm

Can these signals make problems? If we need to add the components, could you give me an example of schematics diagram? In the schematics of PCA10040, I can't see any components, those are just connected to ATSAM processor.

2. I think it is 5mA around.

I need your help.

RE: floating reset pin

MartinBL — Wed, 11 Jul 2018 14:42:23 GMT

Hi,

1. The reset pin is pulled high by an internal pull-up resistor, so it is usually fine to leave it unconnected. However, if the reset pin is connected to long and/or exposed PCB traces then maybe it can pick up some noise and reset the chip. This also applies to the SWD traces.

2. It could be, but it is difficult to say. It would be helpful if you could provide some numbers or measurements? How much current are we talking about?