K21 - DryIce data loss, high VBAT current

[michaelhaben]

We're using the DryIce tamper module in a K21, and seeing unexplained loss of stored data even with all tamper-sources disabled.

Our suspicion was that the VBAT line was somehow glitching below the DryIce minimum limit of 1.71V, despite having a 1kohm/1uF RC filter on it - in the course of investigation, we've seen up to 28uA being drawn by the K21 VBAT line (28mV across the 1k resistor) when the main power-supply is switched off, way above any figure given in the datasheet!  So please can anyone tell me...

1.  Does VBAT supply any K21 modules other than DryIce and the RTC?

2.  What could be causing such a high current to be drawn?

3.  Is anyone using the K21 DryIce tamper module successfully and reliably?  Any tips to share?

thanks,  Mike

[michaelhaben]

Hi Fang,

  we are definitely seeing ~30uA being drawn by the VBAT pin, but only from abot 2 seconds after power-up, indicating that we might be configuring the DryIce wrongly.  I can't find any information in the datasheet on the drive-strength (output current) of the tamper-pins, please can you tell me where to find this info?

thank you,  Mike H.

[miduo]

Hi,

Answer to your questions:

1. Yes, VBAT is independent power supply for DryIce and RTC, no others.

2. It is really hard to give more detail information regarding this. The Drylce more detail information need an NDA.

[michaelhaben]

Thank you for confirming that Vbat supplies only RTC and DryIce. We signed

an NDA at the start of the project, and have the DryIce example code etc.

[miduo]

Hi, Michael

I see that you had submit a case regarding this issue. I will help you on this regard. Would you mind sent me the schematic? I would like to check the hardware connection first, especially the connect of VBAT and main VDD.

[michaelhaben]

Hi Fang, I hope you can see this - 

I tried to reply to your email, but received the response below.  Do you have a personal email address I can send the schematic to?

Thank you,  Mike H.

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[michaelhaben]

Further measurements on a different board: once the DryIce has been configured, with the main MCU power OFF, I am seeing a steady 19uA being drawn by the VBAT pin.  With MCU power ON, the VBAT current is higher, typically 32 - 40uA but sometimes up to 70-80uA!

[michaelhaben]

Hi Fang, please can you tell me how to send the schematic of our circuit

to you?  I'd rather not post it on a public forum!

thanks,  Mike