I'm using a NT3H2111 (QFN package) and commuincate with it over the i2c interface and a busy bee efm8b2 microcontroller. The NT3H2111 is supplied with 3.3v, has 3kOhm pull ups on sda and scl and 0.1uF capaictor next to its vcc pin.
At first I did only read 7 Bytes of the config register (address 0x3A) just for testing the busy bee smbus driver. That test reading was running for at least a week or two, while I was working on other stuff. Today I started to develop the communction between the uC and the ntag, so the manual stated that a i2c read and write config registers always transfers 16bytes. So I changed that from my 7byte to 16 and added a write accees to the config register ( stetting some values in the NC_REG at the config address, remaining bytes are kept to their default values). And this kills my ntag. I killed now the fourth chip, after I read more than the 7bytes and/or start writing the config reg. The chip dies after 4 or 5 times doing that. Looking on the SDA and SCL line then, they both are pulled to gnd when the uC tries to start the communiction. I can still access the ntag with my Smartphone (ndef data), but erase or wirting the config regsiters does not work either after the i2c communictation starts failing.
I measured everything around the ntag on my pcb, there is defenetly no shortcut, and 3kOhm pull ups should be fine also. And the test reading was running for at least a week, like I already stated.
Has anyone faced a issue like that? I'm totally confused.