AM335x ext_wakeup0 and RTC-only Mode

Stefano Bisi

Goodmorning,

We are planning to use AM335x rev 2 in RTC-only mode, whit internal LDO. On SPRUH73 rev h 8.1.4.3.5 figure 8-5 there is signal ext_wakeup0 from PMIC to AM335x.

On 8.1.4.3.6 is stated that EXT_WAKEUP0 must be connected to a wakeup source but what it mean ? Which is a wakeup source if I want that AM335x start up when Main supply came and shut down when main supply gone ?

I'm a bit confused about startup sequence.

Thank in advance

Stefano

over 12 years ago

0 Biser Gatchev-XID over 12 years ago

TI__Guru**** 393215 points

Hi Stefano,

What PMIC do you plan to use?

0 Stefano Bisi over 12 years ago in reply to Biser Gatchev-XID

Intellectual 460 points

Sorry...

I'm planning to use tps65910a31

0 Biser Gatchev-XID over 12 years ago in reply to Stefano Bisi

TI__Guru**** 393215 points

If you don't plan to use low-power modes during operation then EXT_WAKEUP isn't needed and it should be tied to GND. If you plan to switch to RTC-only mode during operation, then you have to tie this pin to a wakeup source (e. g. a push-button, interrupt source or something like that) in order to bring the processor out of RTC-only mode back to active mode.

0 Stefano Bisi over 12 years ago in reply to Biser Gatchev-XID

Intellectual 460 points

On our system we plan to have only 2 states, On and Off and we have a backup battery to feed RTC.

For me is not clear what happen when main supply goes up when AM335x is in RTC-only mode.

TPS65910A31 should turn on and start to generate the turn on sequence of supply or wait PMIC_pwr_enable signal from AM335x ?

Why on 8.1.4.3.6 seem that EXT_WAKEUP0 need some kind of connection ?

Thank in advance

Stefano

0 Biser Gatchev-XID over 12 years ago in reply to Stefano Bisi

TI__Guru**** 393215 points

Hi Stefano,

I understand now. I think that in your case nothing special will be needed. When the main supply comes the PMIC will simply turn on at issue a power-on reset to the processor. When main supply is removed, the VRTC supply will stay at 1.8V as long as a backup supply is available and the RTC will continue to count time.

Processors

Processors forum

AM335x ext_wakeup0 and RTC-only Mode