NTAG 5 link energy harvesting and pass-through mode

[gpira]

Hi everyone,

I'm currently developing an application the NTAG 5 link.

I want to use the NFC to reprogram some data into the MCU's memory and during this phase I would like to power the MCU through Vout. 

During the Normal Operation the Micro will be powered by another source (a regulator) and I want to leave the NTAG shutted down.

For that I was planning to connect Vout to the global Vcc (the output of my regulator, not the NTAG's pin), and to use a MCU's pin to drive the NTAG's Vcc pin ( quite much as it's done in the NTAG I2C plus Explorer Kit).

Is it feasible? Should I place a diode against inversion to protect Vout when the system is powered by the regulator? Can I use the passthrough mode or is it mandatory that Vout and Vcc are connected directly together?

I attached a simplified scheme of my application for clarity.

Thanks.

 Best regards,

Giacomo

[gpira]

Thanks Kelly for your kind reply.

I had already seen the schematics before writing here, but that doesn't answer my question.

In the datasheet (par. 8.5 Energy Harvesting) it is said that :

"VOUT pin shall be kept floating (not connected) in case energy harvesting feature is not used. If energy harvesting is disabled, pin will be connected to GND internally."

As I said before, I want to implement a double power source for my system, one that comes from the NFC tag and the other from a regulator. The key fact is that only one at the time should be active. 

When the harvesting is on I shouldn't have any problems.

When it is disabled instead, it is internally connected to GND, and if the regulator starts to drive his output , I'll have a short on Vout.

I considered to add a diode between Vcc and Vout, but I would prefer not to, because of the voltage drop on the diode itself. Are there any other solutions? Or am I missing something and the diode isn't needed at all?

Best regards,

Giacomo

[KellyLi · Accepted solution]

Hello gpira,

If you do not use this function, then this pin is directly grounded, which should be considered based on power consumption. If you add diodes, will it increase power consumption? So, there is no need to add diodes. Please also consider it in combination with your actual application

Thank you for your cooperation
Best regards,
Kelly

[gpira]

Thanks Kelly.

So, if i understand correctly as long as I am able to drive Vcc properly , I should not have any problems with my application.

I only have one question left regarding Vout. Has it some kind of protection (against inversion, overcurrents,...) or should I implement it myself?

I couldn't find anything on the datasheet or in the application notes.

Thanks.

Best regards,

Giacomo

[KellyLi]

Hello gpira,

Vout is Energy harvesting voltage output pin and the default status keeps floating, If you want to use it, please refer to the design of NXP development board:

Thank you for your cooperation
Best regards,
Kelly

[KellyLi]

Hello gpira,

I had checked your scheme and understood your application, I have a little comment for you:

NTAG is powered by GPIO, you need to consider whether the drive capability of GPIO is required or not.

If you set NTAG to work on pass-through mode, in pass-through mode, if the tag is not VCC
powered, the SRAM mirror is disabled and reading out the bytes related to the SRAM mirror position would return the values from the EEPROM.

Please consider your application according to NTAG working modes.

Thank you for your cooperation
Best regards,
Kelly