54l15. UART communication issue with low temperature.

[twistwind2]

Hello,

We developped a new rf board with 54l15 µc.

We discovered our UART communication have some errors with -16 °. At -20 ° the device doesn't respond.

I changed our devicetree to use external crystal, but i still have UART errors at -16°

&lfxo {
	load-capacitors = "external";
};

&hfxo {
	load-capacitors = "external";
};

I tried with your uart sample echo_bot and i have got same UART communication issue with low temperature, with our dts.

I can see crystal is launched here :

 

internal oscillator is not configured

we use sdk 2.9.0 so i tried with 3.2.3 sdk version.

The results are not the same. I have got response even with -40 ° but still errors at - 18°.

There is a big difference between 2.9.0 and 3.2.3, crystal is not running:

Do you know where is the issue?

[Vidar Berg]

Hello,

Please request the HFXO through the "onoff" API as shown in the hf_clock_request() function here: https://github.com/nrfconnect/sdk-nrf/blob/f35cddd506a9a779305feb0f52fcbf99b03bee23/tests/drivers/grtc/grtc_clk_output/src/main.c#L49 at the beginning of main() if you are not already doing that. This API is globally reference counted, which means the HFXO will be kept running even if the bluetooth stack or another SDK module releases its request for this clock source. 

Best regards,

Vidar

[twistwind2]

Hi Vidar, i integrated your solution into your sample : it is working. it solves the issue. Thanks for your response. I have got 2 questions: Is this solution permit to have efficient low power? (into future our product needs to run with ~= 10 µA max). Into our dts, i selected clock like this. here: 

&clock {

    status = "okay";

    hfclk {

        source = "external";

    };

    lfclk {

        source = "xtal";

    };

};

This solution should be enougth to work with low temperature without onoff clock request, rigth?

I don't understand why XO is not running with echo bot sample or our project (No ble for moment)