OMAPL132 RTC

Vishnu Harihar1

Hi There,

We are using internal RTC of OMAPL132 with 20ppm external crystal.

There is a remarkable 5 or 6 second delay per day and it is varying with different cards, even if we are running from main supply (not from backup battery).

We tried different values of crystal load capacitance, but RTC failed again.

Any help will be appreciated.

Thanks

Vishnu

over 9 years ago

0 Senthilkumar Srinivasan over 9 years ago

TI__Mastermind 43660 points

Hello Vishnu,

The maximum delay for 20ppm crystal at 25 deg.C is 1.74 second per day. The physical parameter like temperature variation may increase this delay further.

You can see some recommendations for RTC accuracy in below e2e links.

https://e2e.ti.com/support/dsp/omap_applications_processors/int_omapl1x_dsps/f/116/t/37515.aspx

https://e2e.ti.com/support/dsp/omap_applications_processors/int_omapl1x_dsps/f/116/t/12648.aspx

http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/p/103965/368116.aspx#368116

http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/p/115332/409907.aspx#409907

Moreover, there are compensation registers included to handle this if the time is drifting by a small amount in one direction only: COMPMSB + COMPLSB.

If it's an inconsistent drift, you should focus on the crystal oscillator circuit itself to see if tweaking any external components to center the oscillator frequency. It might not be a bad idea to try other crystals too, if possible.

Regards,
Senthil

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OMAPL132 RTC