EM7565 : Required Shutdown Sequence


#1

Hi

In Rev 7 of the PTS pg53 5 : Power

Required Shutdown Sequence
Warning: To avoid causing issues with the file system, follow this shutdown sequence.
1. Drive Full_Card_Power_Off# low.
2. Wait for at least t_pwr_off_seq seconds.
3. Remove power.

and
t_pwr_off_seq 21.5 25 Seconds

Is this a “must” requirement or a “optional” requirement ?

If it’s a must I guess this means we need a local power source (e.g. battery or supercap) to provide a UPS function for the radio - am I correct?

Thanks in advance

John


#2

@johnofleek,

It is what it says, if you don’t shut the unit down correctly then while we have taken as many precautions against memory corruption as we can, we have seen it happen if the power is just cut (some applications, I know, cannot avoid this). Worst case scenario it can take a while to shut down but this is very much the exception in reality it takes a few seconds to detach and tidy the flash up.

Regards

Matt


#3

Thanks Matt

It would be helpful to have some additional information so that a minimum safe energy storage requirement can be calculated

  • worst case shut down current profile vs time
  • the minimum operating voltage (flash not corrupted)

Is this information available?

Thanks

John


#4

@johnofleek,

Unfortunately no this is not available, the general recommendation is to keep it connected to the power supply and not to a cap as it probably would not be enough and if it was probably have too much of a cost/design impact.

The minimum operating voltage before the unit switches off is stated in the PTS @ 3.135V.

Regards

Matt


#5

Maybe the baseband CPU(s) (MDM9250) runs down to 1.8V (maybe 1.5V or lower) as well as the flash / ram? - unless of course there’s a brown out cct in the module?

I’d guess the spec of min 3.125V is for correct radio operation - the baseband will just switch the radio off (airplane mode) when <3.125V is applied - am I correct?

I’m concerned about flash corruption following power loss. I’m trying to estimate how much power reserve to design in to avoid occasional damage to the module. Maybe we should ignore the possibility of flash corruption but at this point we have no way of reviewing the risk of corruption as we only have the datasheet spec requirement to work from

Thanks
John


#6

John,

If your voltage drops below the spec’ed 3.125V then you are going to be outside of the spec and into unknown territory which there is no way to answer what will happen.

Regards

Matt