Hello,
I'm evaluating ST25DV for an application and am trying to characterize max available VEH voltage. I'm using STEVAL-SMARTAG1 board, and monitoring VEH output while enabling "Energy Harvesting" feature on the "NFC Tap" app. I can't seem to get above 3.4V on the VEH pin.
I've used both the embedded antenna, and as well as an external antenna (at which point I cut the embedded antenna traces). With the external antenna I made sure it is tuned to 13.56MHz while connected to ST25DV front end. I can confirm that the induced voltage is 9V (which seems to be due a clamping because when I disconnect the ST25DV I can get induced voltages well over 20V).
I'm trying to understand what is limiting VEH to 3.4V when I can clearly get quite a bit of voltage from the coil. The 3.4V limit seems to be also due to a clamp, because irrespective of the antenna position the voltage won't go above that, period. Once I move the antenna sufficiently far away, at some distance the VEH starts to quickly drop.
Is VEH indeed hard-limited to 3.4V internally, or am I missing a setting?
