TPS65920 duty cycle problem on 32k clock

Philippe MAIRE

Hi,

On my OMAP board, the 32,768 Hz clock is a square clock provided by an external RTC.

The duty cycle of the clock is at about 40%, and I just noticed there is a requirement of 45/55% in the SWCS037E datasheet.

The OMAP on its side does not require a particular duty cycle on this clock.

What could be the consequences of this duty cycle issue on the PMIC ? I won't be using the PMIC's real time clock, but I think that the 32k is used widely in the PMIC for other functions.

Regards

Philippe

over 14 years ago

0 Gandhar Dighe over 14 years ago

TI__Genius 15100 points

Hi Philippe,

The slow clock if at 40% duty cycle will still be ok, accuracy for slow speeds is not very important. You are anyway not using RTC in this device, so it is ok. . As you have seen it is used by the power state machine, USB, BCI and keypad.

There is no characterization/validation data to show what can happen if the duty cycle is lower than the specs. I would not use such a duty cycle in a production platform to avoid any unknown issues.

I hope this helps.

0 DavidVescovi over 14 years ago in reply to Gandhar Dighe

Genius 5470 points

Also, be very carefull and check rise times, they need to be fast or you will have issues with the watchdog and general purpose timers of the OMAP. We have seen the timers go nuts with a poor quality 32khz clock input.

0 Gandhar Dighe over 14 years ago in reply to DavidVescovi

TI__Genius 15100 points

Hi David,

Thanks for sharing this.

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TPS65920 duty cycle problem on 32k clock