Low Power mode in ST25DV04KC Tag

[Nikhil D&K]

Hello Developers,

I am currently developing a low power solution incoperating STM32L4 controller and ST25DV04KC tags (8-pin package). We are using GPO interrupts for field change, FTM write/read operation notification. 

Now what i am looking for is a solution, where GPO interrupts will wake controller from STOP2 mode and perform nfc operation based on interrupt source. But at the same time i also want to put  ST25DV04KC tag in low power mode. Referring the ST2504KC datasheet, i know that i can Disable the RF Activity but that will also stop the GPO functionality. 

So can anyone suggest what are the best possible configurations for ST25DV04KC tag, such that GPO functionality of ST25DV tag doesn't get effected while it's in low power mode. 

Looking for a quick response. Thanks in advance. 

[JL. Lebon]

Hello, 

I can suggest you read the application note AN5733 (https://www.st.com/resource/en/application_note/an5733-using-st25dvi2c-series-for-ultralow-power-applications-stmicroelectronics.pdf) which explain how to reduce the power consumption to the bare minimum. It is mainly written for eh 12 pin version, but at end of page 6 you have the explanation on how to do the same thing with 8 pins version.
Concerning the GPO interrupts, they are working even if VCC is not present (except field falling interruption) as long as the pull-up on the GPO pin is present for the 8 pins version of VDGC is powered for the 12 pins version.
So, the best thing to do is to either use the LPD pin (if 12 pin version is used) or to directly shutdown the VCC (with cautions explained in the AN): in both cases, GPO interrupts will still work if the pull-up is powered (or VDCG is powered for the 12 pin padage).
If you put the RF in RF sleep or RF off mode, you will only get the Field rising/falling interrupt. But the gain on power supply consumption in this mode is very low.
Best regards.

[Nikhil D&K]

Hello @JL. Lebon,

In our current version of product, we are using 8 pin version of ST25DVKC. We have connected a load switch to trigger on and off NFC section. Also the GPO pin is externally pulled up as per datasheet and MCU is configured to detect falling edge.

Needed Flow :

1. Device in Stop 2 mode, with NFC GPO interrupt configured and working. NFC GPO interrupt should work (detect events of RF activity like ftm write/read etc.) and NFC section triggered OFF. 

2. As soon as GPO interrupt detected, trigger on NFC section. Initalize I2C interface and read interrupt source and perform action accordingly.

Now when i trigger off the NFC section, issue is I am getting interrupt on GPO pin even when external pull up is connected. Also which stop it from entering stop2 mode. 

So can you let me know what could be the possible issue ?

[Rene Lenerve]

Hi @Nikhil D&K ,

ST25DVKC GPO can have multiple configuration, the one interesting for you seems to be field change detection when entering STOP2 mode. If no change are made on the field GPO should not raised interrupt.

Can you give us the configuration of the GPO when entering STOP2 mode?

Are you sure there is no perturbation on the GPO Line when triggering off NFC section that can be interpreted as a GPO interrupt?

Kind Regards.

[Nikhil D&K]

Hello @Rene Lenerve ,

Configuration of the GPO:

The GPO pin of NFC tag is configured to generate interrupts for FIELD_CHANGE, RF_GET_MSG, RF_PUT_MSG. 

On controller side pin is configured to detect falling edge with no software pull-up attached. 

And we have checked on the interrupt line on triggering the NFC off, the GPO line doesn't get effected and it's stays high due to external pull up   

[JL. Lebon · Accepted solution]

Hello, 
When the FIELD_CHANGE interrupt is enabled, the interrupt is always triggered when RF field is rising.
When RF field is falling, it depends on the power on the VCC pin. If VCC is present, an interrupt is triggered to indicate the falling RF field. If VCC is not present, nothing happens on the GPO pin (no interruption triggered, value is the one of the pull-up).
Is it not the behavior you are expecting?
Best regards.