LPC55xx Power consumption when in RESET

[MartinHo]

Hi,

I'm implementing a Battery backup for the RTC of the LPC55xx MCU. Looking at Table 17 of the Datasheet (LPC55S3X-LPC552X Rev. 1.8) I see that in deep power-down with the RTC enabled the typical current is 790nA.

But I'm planning to use an external RESET controller, who will hold the MCU in RESET when the Supply voltage falls below about 2.5V (I'm using a 3.3V supply).

My questions:

1) If the MCU is in active mode and I apply  RESETN=LOW what will the typical current be ?

2) In the same condition, will the RTC remain enabled ?

best regards

Martin

[FelipeGarcia · Accepted solution]

Hi Martin,

Please check my answers below:

1. I am sorry but this was not tested so we do not have the current consumption for this specific scenario.

2. RTC will not be active, please check below table from User Manual. “Rst” indicates that the sub domain is reset by the associated reset source, and “Act” indicates that it remains active and does not change state in response to that reset source.

Hope it helps!

Best regards,

Felipe

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[MartinHo]

Hi Felipe,

Thanks for the answer. Unfortunately this means that the RTC of the LPC55xx Family is practically useless if You have to wake the MCU with the RESETn Input. This together with the uncertainty of power consul in RESETn state, is a NOGO for the internal RTC in my design.

I will go for an external RTC ( adding some unexpected costs and components ).

I Understand that RTC's inside MCU's are a problem, but on a chip like the LCP55xx with so excellent power-saving possibilities, the low attention to the usability cases for the RTC is really a shame.

best regards

Martin