TRF7970A: TRF7970A

Hello Mike,

Mike Evans1 said:

Is this the right part for the application?

If you only want to use tag mode and never a reader mode, then it is not the right part and I can make another suggestion. Please clarify this.

Hi Ralph -

The Product needs to operate as a Reader as well as perform Tap to Pair operations.

I am looking for more detailed information on the Tap to Pair process, whether or not the radio has to be ON to perform this task, and if this is the right component to perform both operations listed above.

Hello Mike,

The pairing operations mentioned in the datasheet were definitely more with the device being the reader in mind. It can certainly do it as a tag too, but it isn't optimized to do so in the sense that you will need to operate with the RF receivers on and that would require 9-10.5mA current draw from the IC (depending on 3V vs 5V operating mode).

The transmitting portion of the radio would not be on which is where the heavier current draws come from.

We wouldn't have an alternate part, so if the 9-10.5mA current draw is too much, then you probably need to look into other solution. The functionality you are looking for was not an area we focused on with our NFC portfolio. Our usual 'tap to pair' device is the RF430CL330H transponder but that cannot be a Reader and wouldn't work for your needs.

Hi Ralph -

IC is powered with 3.3V.

Tag Mode

I was thinking that this would be the default mode we would operate in.  NFC IC would be configured as a  Reader/Writer and in the Power Down state (EN=0, EN=0) which would draw 0.5uA typ.

We will want the NFC IC to operate as a passive Target (6.1.3 & 6.1.3.2) after activation occurs, which is when a sufficient RF level (selectable) is detected.  We would remain operating in this state unless we were given the command to  become a Reader.  Even then, we would perform this short operation and then default back to Power Down state and operate as a Target.

I see this as a potential way to meet our requirements without excessive (continuous) power consumption.  This is a concern since we a Battery powered. 

The mode of Ion1 (supply current without antenna driver current 10.5mA typ, 14mA max) is only when the device experiences activation as a Target.  Correct?

Please review my analysis above and provide feedback.

Thanks.    

Hello Mike,

Thanks for raising that point, in my attempt to try and get some information out over the weekend, I had overlooked (forgotten, really) how the RF measurement system works with Power Down mode - I was more focused on the receiver needing to be on, but that's only for data.

You are correct about the Ion1 current being when you need to receive data, and you can remain in a lower power mode while waiting for an RF field to be presented.

Have you assessed how much battery capacity you'd have versus the amount of power needed to read tags? During the reading process, the RF field will need to be on continuously. Not sure how much data would be read, what sort of tag technology you'd use, or what kind of read range you are trying to achieve with that portion of the application.