c6748 RTC crystal

Hi Paul

Paul said:

Can you suggest a small battery that operates at the 1.4v level required for the RTC?

I don't have a ready answer for this. Maybe someone from the community can pitch in on this.

Paul said:

If I don't want to use the RTC will the rest of the device still function correctly without the 32.768k crystal?

Yes, the device will function without issues, if you opt to not have RTC functional in your design. You should follow the recommendations in the datasheet on how to tie the RTC pins if un-used.

Paul said:

I know that the datasheet indicates that this is the case but I have experience of other parts which use the rtc crystal for some of the low power modes?

There are no hard dependencies on the RTC crystal for low power mode. There are 2 modes that make use of RTC.

1) RTC only mode: This is essentially a mode in which you can power off the rest of the device power rails (core and IO) and just leave RTC running. However, in this mode there is no "wake up" event to re-enable the device (c6748) supplies directly. You would need the "decision making" entity on when to re-apply power , out side the device (connect a wake up event to the PMIC or a microcontroller that can indicate when to re-apply power to the chip)

2) Deep Sleep Mode: One of the wake up events for this mode is the RTC ALARM signal. However if you chose to use the Deep Sleep mode , you can also use DEEPSLEEP pin as the wake up event , so you can opt to not use RTC in this ode.

Both of these modes are described in the Power Management chapter in the system guide

http://focus.ti.com/lit/ug/sprugj7d/sprugj7d.pdf

Besids these modes, you should not have any dependency on RTC for device low power modes.

Hope this helps.

Regards

Mukul