Issue with BLE connection using 32k XTAL

[KEOPS]

Hi,

I have an issue in my project using BLE connection (GATT). I configured the BLE stack to use an external 32k XTAL (NRF_CLOCK_LF_SRC_XTAL) or (NRF_CLOCK_LF_SRC_RC)

#define NRF_LFCLK_RC_CONFIG                                         \
{                                                                   \
	.source       = 0,												\
	.rc_ctiv      = 16,												\
	.rc_temp_ctiv = 2,												\
	.accuracy     = 1												\
}

#define NRF_LFCLK_XTAL_CONFIG                                       \
{                                                                   \
	.source       = 1,												\
	.rc_ctiv      = 0,												\
	.rc_temp_ctiv = 0,												\
	.accuracy     = 7												\
}

In both cases, when i try to connect with nrf connect android app, it gives me this result, no matter how many tries and with different smartphones

 

I captured the air trafic with nrf sniffer

But when i change the stack configuration to use the NRF_CLOCK_LF_SRC_SYNTH, it works well !! 

#define NRF_LFCLK_SYNTH_CONFIG                                       \
{                                                                   \
	.source       = 2,												\
	.rc_ctiv      = 0,												\
	.rc_temp_ctiv = 0,												\
	.accuracy     = 1												\
}

Here is my configuration : 

HW: proprietary card with Laird BL653 (based on nrf52833)

SW : SDK_17.0.2, S140_7.2.0

Do you have any idea about the issue ? and why it works with NRF_CLOCK_LF_SRC_SYNTH and not with NRF_CLOCK_LF_SRC_XTAL or NRF_CLOCK_LF_SRC_RC ?

Thanks

[Jared]

Hi,

Could you share the full part number and datasheet of the external LF crystal? What size is the parallel load capacitors of the crystal?

regards

Jared