nRF52832 output resistance 2.7 Ohm?

[Pero Krivic]

Hello, I have just started evaluating SoC nRF52832 and have built a custom board based on recommended diagram from the datasheet chapter 53.3. Actually, the board diagram and layout was published in the official Eagle 9.1.0 CAD examples release and follows the layout guidelines from Nordic well.

I've managed to get started with nRF52 SDK, Keil uVision and ST-Link and made my blinky examples running. Yaaay! However, I had no success in turning on the ble_uart example. I couldn't see the device advertising. I also tried to pick up any signal at the chip output with my 4GHz / 20GSps scope, but there was none.

Lastly, I decided to check if there is maybe some short circuit at the pin output and I measured 2.7 Ohm DC resistance between ANT pin and the ground. Is this value plausible DC resistance (as far as I understand there is a balun at the output pin) or am I dealing with potential short-circuit due to the soldering failure?

Best regards,

W.

[Andreas]

Hi,

 

Copied answer from this thread:

The short impedance of the ANT pin is as it should be. Even full reflection at 4 dBm output power it should not take damage. You can dial this down a bit, -8dBm should be possible to receive if you put the phone/measuring device right next to the PCB and have plenty margin to the levels where it might hurt. You can also look at the current consumption when set up as a TX carrier.

 

If you do not see any radio activity it might be that the crystal is either not starting or incorrectly calibrated. Have you verified this? The load caps shall be approximately 2*CL-4pF, CL is specified for your crystal.

The DC resistance is fine, but even if there is a short, you should see some radio activity. You should therefore look into the current consumption, and possibly crystal verification. You might want to use the radio test example for this, or just load a hex that sets up a TX carrier. Also have you successfully loaded the Softdevice when testing the BLE_uart example?

Best regards,

Andreas

[Pero Krivic]

Hi Andreas, thanks for the answer. I downloaded Softdevice example according the tutorial guidelines and haven't seen any error messages, I assume it went OK. In any case, I've seen your earlier response, I appreciate it and will check out the oscillator and current consumption. Talk to you soon,

W.

[Andreas]

Hi,

 

OK, the Softdevice should be properly flashed then. I still recommend you try to test this using the radio test example to eliminate possible sources of error. Let me know how it goes.

 

Best regards,

Andreas

[Pero Krivic]

I managed to lose 32M quartz crystal during  the soldering, As I'm waiting for the new one, I measured if there are any bad traces on the xtal footprint and I've seen that one end of the xtal is tied to the 3V3. Is it supposed to be so in the chip, or I managed to brick it?

[Andreas]

Hi,

 

The crystal is not supposed to be tied to 3.3V. I am not surprised that this is keeping it from working, but it might not be bricked. It is hard to say, we really have not characterized the behaviour when this is done.

 

Best regards,

Andreas