How to source RTC in hardware on LPC55s06

[Landgrebe]

Hello

I'm trying to source the RTC when the power is shut down to keep the clock running. Right now my design is developed with as showed. 

My problem is that my coin cell battery drains very fast (1-1.5 hours) and I think its because the battery is sourcing the VBAT_PMU, VDDA and VREFP, and therefore drain the battery fast. As I read on Solved: Re: Recommended circuit for RTC Battery backup - NXP Community the VBAT_PMU is the only one that has to be supplied to keep the RTC running. 
My first thought was just to let the VBAT source the VBAT_PMU no matter if the power was on or off. The problem in that case is the datasheet section 6.1, table 3 - "VDDA" describes: 
"Analog supply voltage. At PCB level, has to
be tied to main supply (VBAT_PMU, VBAT_
DCDC"

Is there anyone who can explain how to correctly source the RTC (VBAT_PMU), and still retain the description above? 

Thanks!

/Landgrebe

[_Leo_]

Thanks for contacting our technical support.

It is recommended to follow the power supply configuration described in AN13033 and AN12325. To avoid that your coin cell battery drains very fast and continue sourcing the RTC, it is necessary to manage available power modes, specifically the DEEP POWER-DOWN mode, where Power Domain Always On (PD_AO) is the only one on.

Hope it helps you.

Have a nice day

[Landgrebe]

Hi Leo 

I have made som changes, and got something to work. 

I'm using the BOD when the power supply is disconnected, to set it into deep power down. 

Some off it works. but it doesn't look like it finishes all off the funtionality in POWER_EnterDeepPowerDown, and I can't debug the code while the 3V3 power is disconnected. 

If I set the POWER_EnterDeepPowerDown before disconnecting the power (3V3), the the power consumption is around 100uA on the Vbat pin. But if I let it disconnect the power while its still running as usual, the power consumption is about 1200uA.

I know it turns off something inside off the POWER_EnterDeepPowerDown function, because if i leave it outcomment in the BOD then the power consumption is about  2mA.

Do you have any idea how to get the lpc55s06 to EnterDeepPowerDown, while the VDD is not supplied? 

best regard 
Landgrebe
@_Leo_