TPS65920 supports RTC timer while in back up mode?

Hi Gandhar,

after a deeper discussion with the customer I understood that the Vbat can be always connected.

so actually we can stay in "wait on"  mode with fully function of Vbrtc and Vrrtc and can get "switch on request" as indicate in the dataasheet in the EPC chapter

as said , the application would like to be in sleep mode for 10 minuts, search mode for 4 minutes and then depends on the search results to go to operational mode

or back to sleep mode.

I thought on the following scenario - please let me know if it's possible?

Sleep mode - PMU is in "wait on" mode. 10 minutes need to be counted. FPGA & OMAP are in off mode.

can we use the RTC to count 10 minutes? any other idea?

Search Mode - the customer has an Ethernet part which can send a "switch on request" if he gets a LAN packet.

PMU needs to trigger the power supply Enable of this part.

can the PMU give interrupt to the power supply part while being in wait on? while being in active mode?  idea is that after the 10 minutes timer over, the PMU will

gives '1' via GPIO to turn on the ethernet comm power supply and wait to the switch on request.

OMAP is still in reset, off.

PMU will get the "switch on request" from the ethernet and release the reset of the OMAP which will turn on from sleep .

if "switch on request" won't arrive, the PMU will go back to sleep/"wait on" mode after four minutes and disable the power supply of the ethernet .

it may be hard to understand so maybe we can discuss it by phone off line?

Happy new year!!

Amit

Hi Amit,

We can discuss off line. I thought of clarifying some things in this reply.

PMU in wait mode is essentially an OFF state. You will need to be in BACKUP mode for counting timer (using RTC). As said earlier that 32K is ON in backup mode and counting is possible. 32K is ON in all modes except wait on. WaitOn mode is the state when battery is connected to the device and it is ready to power ON on a startup event.

PMU interrupt is generally/always tied to OMAP. INT1 is the interrupt on TPS65920. So, sending interrupt to LAN device is not possible. In backup mode only the backup domain is powered. So, using GPIO to send signal to LAN power supply is not possible. OMAP can write commands to set GPIO, but this will need OMAP to be active.

Based on the interrupt from TPS device to OMAP, OMAP can write to TPS to send a GPIO signal. Can you ask (or do you know) if this is possible for OMAP?

I think it is possible, but is betetr to ask some OMAP support person. If OMAP is OFF this is surely not possible. I am talking of this scenario if OMAP is in some low power state and can still communicate with TPS65920.

Regards,

Gandhar.

thanks!

I would like to summary the correct way of doing this application according to your answer.

Sleep mode - PMU is in "backup" mode.  FPGA & OMAP are in off mode. no power is apply to OMAP Vcore, Vio etc.

after counting 10 minutes. the PMU will give interrupt to the OMAP .OMAP will acknoledge and turn on the PMU with all the DCDCs

(question - how the OMAP gives the acknoledge if it hasn't have any Vcc?)

after the PMU waken up by the OMAP , the PMU is in active mode. 

the OMAP, which is wake up in the lowest power mode possible, will enable the ethernet "wake on LAN".

next step is to wake up the ethernet device and wait in search mode that a LAN packet will arrive.

Search Mode - the Ethernet part can send a "switch on request" if he gets a LAN packet. the switch on request will turn the OMAP to full active .

if packet didn't arrive, OMAP will give an order to PMU to go back to backup mode.

customer isn't going to use a backup mode. should he tie the backup battery input to Vbat or leave it floating?

thanks!

Amit

Hi Gandhar,

a minute before I give up and recommend the customer to use an external MSP430 to run the 10 minutes timer on sleeping time, and then four minutes on search mode,

I would like to check regarding the PMU.

I saw that the PMU can raise the INT1 ball when the alarm gives a trigger - after 10 minuts ended.

any chance I can connect the INT1 to the ethernet enable?

the "switch.on.request." can be connected to the OMAP  and trigger it once a LAN packet had received?

if a sw.on.req hadn't arrived (didn't get a packet) & RTC=4minutes, then we go back to position A in the state machine, reset the 10 minutes timer and go to sleep?

I prefer not to activate the OMAP as the OMAP wake up with its DDR memory which consume power.

thanks!!

Amit

Hi Amit,

INT1 can be connected to any processor that can interpret an interrupt and take necessary action. If the ethernet device is capable of that then its fine. Make sure connecting INT1 to something other than OMAP doesnt have any effect on OMAP functionality (in case it is used for something like keypress events or alike).

Regards,

Gandhar.

Hi Amit,

The sequence of replies is not in sync with your questions.

(question - how the OMAP gives the acknoledge if it hasn't have any Vcc?)

You are right, for this to happen OMAP will need to be in low consumption (retention) state.

Regards,

Gandhar.