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.

[Hung Bui]

Yes, the RC oscillators shouldn't be a problem here. Same firmware should be able to run on both chip (if the size fits). I don't understand what you meant here "modules that integrate both the nRF51 and PCB antenna, so I think those issues cannot be helped in our case"

The reference design is made to be used with PCB antenna (as well as other antenna). It should be followed. You should only modify the component values if you do have equipment to tune and match them with the design and material of the product.