we developed a custom board with the iMX537 and the PMIC MC34708 chip.
On the PMIC, there is a coin cell connected (3V CR2032) on the LICELL pin.
If we program the RTC on the CPU, the RTC runs perfect until we cut the power, afterwards, all the RTC registers are reset.
We have tried the same on a (changed) QSBoard and have the same behavior.
While the power is cut, the voltage VSRTS drops from 1.3V to 1.23V and the 32Khz clock keeps running.
Is there anbody who has already successfull used the iMX537 RTC function, so yes can you give me any sugestion where to look for ?
This is the answer that we received from Freescale :
In reply to your Service Request SR 1-894779544:
OK, Got it. Some customers also met the same problem. I just now adjusted power up sequence. Do it like this :
VDD_DIG_PLL(1.3v) supplies for VDDA and 1V3_VGEN1 supplies for VDDAL, SRTC can be kept after cold reset. So please retry it !
How did you program your RTC and which RTC did you program?
Did you program the RTC on the PMIC or the SRTC on the i.MX537?
If you are using Linux, RTC0 will be the processor SRTC and RTC1 will be the PMIC RTC. You will want to use the PMIC RTC ( RTC1 ) for your coin cell backed up RTC.
We use the iMX535 and have a similar (probably the same) issue - I assume we are dealing with the same problem.
First, look at the Errata sheet for your processor. For the iMX535, errata #23 identifies this exact problem. The workaround is to connect an additional circuit to VDDLP pin on the PMIC (shown in errata sheet), however, when we have done that we experienced a rapid battery drain - we are currently investigating how to solve this problem.