PCF2129 OTP refresh

[spicard]

Hello,

We are using the PCF2129T RTC on our design. On some units, we are seeing large time drifts after the we set the initial time/date. Some units can drift as much as +20s/day.

We have found that performing an OTP refresh can reduce the drift significantly. (some units still drift by +1s/day or +2s/day).

From what I understand from the datasheet, the OTP refresh is needed to apply the factory calibration parameters.

If some units can drift that much without the calibration, why the OTP refresh is not automatically applied every time the RTC is power up?

After the initial OTP refresh, is it recommended to perform the OTP refresh periodically? At which interval?

Thank you,

Sebastien

[reyes]

Hi Sebastien

As you may already checked on the datasheet, “Each IC is calibrated during production and testing of the device. The calibration parameters are stored on EPROM cells called One Time Programmable (OTP) cells. It is recommended to process an OTP refresh once after the power is up and the oscillator is operating stable. The OTP refresh takes less than 100 ms to complete.

To perform an OTP refresh, bit OTPR has to be cleared (set to logic 0) and then set to logic 1 again.”

The process of manufacture of the board and soldering of the PCF2129 can cause additional error due to mounting stress, reason of why the OTP refresh needs to be done once the board is mounted in its board and customers need to include it as part of the initialization.

The OTP refresh should ideally be executed as the first instruction after start-up and also after a reset due to an oscillator stop. Other than this, you don’t need to the OTP refresh again as long as the oscillator is kept running.

Regards,

Jose

[spicard]

Hi Jose,

Even if the oscillator will be running for years without stopping, we don't need to perform the OTP refresh during the product life?

Thank you,

Sebastien

[reyes]

Hi Sebastien,

There is no requirements documented for the required interval and there is no tickets from other customers mentioning an issue about this, so, I’m assuming it is not required to refresh the OTP during the product life. However, there is nothing bad to do it once in a while, so, if you prefer, you can include an OTP refresh once a in a while, probably once every month or so is ok.

Regards,

Jose

[BobTGWX]

Hi,

We seem to be having a similar isssue in that a recent batch of equipment using the PCA2129 is showing output frequency  error and corresopnding clock time drift. In our case though the frequency, though incorrect, is consistent over time and temperature. Also the host firmware does perform the OTP reset every time the device restarts on mains power, but this seems to have no effect on the frequency error. If however the battery power is disconnected and restored while the main system power is off, all the units tested so far show a different and much more nearly correct output frequency.