Board does not work when powered by coin cell battery

[bluetooth_mdw]

My nRF52 DK has PCA10040 V1.1.0 2016.34 682272915 on a label.

It works fine when connected to my laptop over USB. If I try to power it from the coin battery underneath though, there's no sign of life. The LED does not light and I can no longer detect its Bluetooth advertising. I have to conclude it has not powered up. I've checked the battery with a multimeter and it's showing 2.78V. I've tried another battery.

Do I need to change a jumper or something? I couldn't find any information that suggests using a battery to provide power requires any kind of special action.

Thanks

Martin

[cbd]

As far as I'm aware whether you use USB, battery or external all power passes through the power switch.

Assuming that the power switch is still on and that the battery is inserted the correct way up (I've got it wrong myself on several occasions) then you're going to need to get a multi-meter out and check some areas of the board.

Above the reset switch are some contacts that look like a circle with a line cut through the middle - SB10, SB11 & SB12.

SB 11 should have roughly your battery voltage on both sides, the others only on one.

You mat find that once inserted and powering up the rest of the board circuitry that the battery voltage is being dragged down too low.

An unloaded battery, even one that is fairly depleted, will give a higher voltage than one that is loaded. I've had plenty of cheap batteries that will appear okay at 2.7 volts and yet once BLE advertising starts the peak current draw drops the voltage below the reset threshold for the MCU.

[bluetooth_mdw]

Thanks for the fast reply.

I just took a new battery, which was supplied with another Nordic board and tried that. Same result. Voltage measured at SB11 was about 2.9V. Battery is in the right way around (very well worth checking!) and the board switched on. Here are some photos (battery shown is not the new one I replaced it with - that's in place when I used the multimeter though).

[bjorn-spockeli]

Hi Martin,

I assume that the nRF52 DK has been flashed with one of the SDK examples and that it is working if you power it through the USB connector?

Could you measure the DEC1-3 voltages to verify that the internal regulators are working as they should.

DEC1 is connected to ground through C4, you should see about ~1.0 V

DEC2 is connected to ground through C6, you should see about ~1.2 V
(unpopulated so just measure the pad on the nRF Side). 

DEC3 is connected to ground through C7, you should see the same voltage as at SB11 (VBAT - the forward voltage of the protection diode)

Best regards

Bjørn

[bluetooth_mdw]

Hi Bjorn

actually I'm running some Zephyr code. But yes, when plugged into USB it works.... it's advertising and I can connect to it over Bluetooth. An LED is also lit. When battery powered, I see no sign of life.

I can't see DEC1-3 on the board. How are they labelled? Approximately where are they positioned?

Thanks

Martin

[bjorn-spockeli]

They are not labeled on the NRF52 DK, hence the references to the decoupling caps C4,C6 and C7, which are labeled on the nRF52 DK,  see the attached schematic and PCB layout.

 PCA10040_Schematic_And_PCB.pdf