Differences in nRF51 chip versions

[Hieu]

We are moving from a PCB using a nRF51822 QFAB module to a newer PCB using an nRF51822 QFAC module.

We observed that with the new QFAC PCB we have a significant connection drop rate, >20 times an hour. Logging of disconnection shows that most of the time it is reason 08, BLE_HCI_CONNECTION_TIMEOUT. Sometimes it is reason 62, BLE_HCI_CONN_FAILED_TO_BE_ESTABLISHED. Meanwhile the same firmware runs very well on the old QFAB PCB, no undesired disconnection.

Is there any difference between the QFAB and QFAC version of the chip that could cause this issue? Perhaps a change in the internal RC oscillator? In our test we use NRF_CLOCK_LFCLKSRC_RC_250_PPM_250MS_CALIBRATION.

[Hieu]

We are using modules that integrate both the nRF51 and PCB antenna, so I think those issues cannot be helped in our case. But if there are still things that has to be adjusted, please advise me, and I will forward it to our PCB designing engineer.

From your answer, I take it the RC oscillators are the same in the two chips? My supervisor kind of want me to be sure about that, aside from finding out what else is wrong with the current design.