ST25R3911 – Possibility to disable VDD_IO in Wake-Up mode

[andrew55529]

Hello,

I’m working with the ST25R3911 NFC reader IC in a battery-powered application where ultra-low power consumption is critical.

1. Is it allowed to completely switch off VDD_IO while VDD is still supplied (e.g., when the device is in Wake-Up mode)?

2. Will the interrupt pin still work in Wake-Up mode if VDD is present but VDD_IO is off?

3. I noticed that even when VDD is off, if VDD_IO is connected, there seems to be additional leakage current. Could you clarify the expected current paths in such cases?

4. Is there any recommended sequence for powering up/down VDD and VDD_IO to avoid unwanted currents or undefined states?

5. Can VDD_IO be powered directly from a microcontroller GPIO pin (to save power by enabling it only when needed)? What is the typical consumption of VDD_IO in idle conditions?

[Ulysses HERNIOSUS]

Hi,

ad 1) Should be possible. But as detailed in 2) you want to get informed, right?

ad 2) VDD_IO is needed to drive digital outputs of the chip including IRQ line. So if you want to be notified wake-up mode about changes in the antenna tank you need to supply this pin.

ad 3) Did you check bits lf_clk_off and out_cl, to assure not driving MCU_CLK?

ad 4) no special recommendation, I am not aware of any problematic sequences.

ad 5) Maybe yes - depending on drive strength of MCU and sinking of inputs of MCU.

How much of unwanted current do you see? I would first thoroughly check point 3) and all possible output pins of the chip to minimize its current before going into switching on/off the VDD_IO.

BR, Ulysses