M24LR I2C pins driven low will RFID mode still work

[Andrew Lohmann_2]

Posted on August 09, 2017 at 15:01

My application will use NFC to either

1. As a passive means of reading an identifier and to store or collect some simple information when a battery is discharged. In this case the I2C bus will be low. Also report that the battery condition.
2. As a passive or powered means of doing the above plus pass information such as BlueTooth and Long range wireless keys transferred via IC2. Perhaps use NFC for some debugging as well.

I appreciate that I2C may need 10 clocks or something to recover from being in the wrong mode. That is fine.

• My question is in (1) will the NFC operate correctly as a passive NFC device. That is with the I2C but pin held low during normal operation?

[Andrew Lohmann_2]

Posted on August 14, 2017 at 14:41

I think the answer is that the I2C bus pins can be low when VCC of the NFC is low. It can't be any other way?

Vout must not be held low eg because the power demanded by other things is too high or else the NFC can not operate in Passive mode. This means I will have to add a power switch of some kind?

[Rene Lenerve · Accepted solution]

Posted on August 21, 2017 at 16:11

Hi

Lohmann.Andrew

,

In the M24LR

http://www.st.com/resource/en/datasheet/m24lr04e-r.pdf

you will found useful information about supply voltage and power conditions. in section 2.6

Table 118 informs about operating conditions also. If VCC is under 1.8V I2C (digital part) will not be activated.

The Analog RF doesn't need VCC to be operational, it uses power from the Reader field.

Hope this will help you.

Best Regards.