topic Re: K21 - DryIce data loss, high VBAT current in Kinetis Microcontrollers

K21 - DryIce data loss, high VBAT current

michaelhaben — Fri, 13 Apr 2018 12:52:29 GMT

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

Re: K21 - DryIce data loss, high VBAT current

miduo — Wed, 18 Apr 2018 03:15:19 GMT

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.

Re: K21 - DryIce data loss, high VBAT current

michaelhaben — Wed, 18 Apr 2018 15:49:42 GMT

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.

Re: K21 - DryIce data loss, high VBAT current

miduo — Thu, 19 Apr 2018 06:26:27 GMT

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.

Re: K21 - DryIce data loss, high VBAT current

michaelhaben — Thu, 19 Apr 2018 14:42:37 GMT

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

Re: K21 - DryIce data loss, high VBAT current

michaelhaben — Fri, 20 Apr 2018 11:04:26 GMT

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.

Re: K21 - DryIce data loss, high VBAT current

michaelhaben — Tue, 24 Apr 2018 09:10:56 GMT

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!

Re: K21 - DryIce data loss, high VBAT current

michaelhaben — Fri, 27 Apr 2018 08:46:22 GMT

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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