Standby mode for NTAG5

[dbwalker0min]

The datasheet is pretty vague about entering and exiting standby mode. I'm working on a battery powered product so I need to get the part in this mode. I initially mistakenly thought that absence of I2C activity would place the part in standby mode, but this is definitely not the case. I can put the part into hard power down mode by asserting HPD and the device current consumption decreases by about 100 µA which matches the power from the data sheet.

Specifically, the datasheet says this about standby mode (section 8.3.5):

To minimize overall current consumption, when the IC is supplied via VCC NTAG 5 link
can be set to standby mode by writing related session bit form NFC or I2C perspective.
The IC will leave standby mode according to configuration when NFC field is detected,
automatically, or HPD pin gets pulled to HIGH for at least 20 μs and released again. In
standby mode the current is typically less than 6 μA.

My specific questions:

• Exactly what is the "related session bit?" Looking through the session registers (section 8.1.4), the only bit I thought that looks pertinent is "AUTO_STANDBY_MODE_EN" in "CONFIG_0_REG" but this bit cannot be written from NFC. The description also says it goes into standby after boot. If you're writing the session register, it seems like it's after boot by definition. Is there an RFU bit or register somewhere you have to write?
• I understand exiting standby mode with NFC field or via the HPD pin, but how does it exit automatically? Any I2C transaction? Chip power cycle? NFC command? Is there some special setup necessary?

I've looked through the drivers, examples, and app notes and haven't seen anything regarding this. Any help you could provide would be appreciated. Specifically, I'm using the NTP53321G0JTTZ.

[lilindian14]

@dbwalker0min any luck with this? I am in a similar situation to you. I finally have the device entering standby mode after hours of debugging. My issue now is getting out of standby mode. All reads using NFC while the device in standby mode results in an empty NDEF message. Any words of wisdom?

[dbwalker0min]

@lilindian14 I think I have it worked out (at least it's working in my application).

The session bit is in the CONFIG_0_REG (I²C address 0x10A1), bit 0. It is confusingly named "AUTO_STANDBY_MODE_EN," but writing it to "1" puts the IC in standby mode.

The part will exit standby mode on any I²C transaction. It will NAK the transaction (it's in standby mode, after all). All of my transactions with the part are done up to three times; if the transaction is NAKed, it will wait 1 ms and try again. The only thing to remember is that if you give it a reset command, it will NAK the last byte. For my processor, this appears like an I²C error. You certainly don't want to keep sending the reset command!

It will also wake up on NFC activity. If you're serious about saving power, you'll periodically put the part back to sleep by writing CONFIG_0_REG.0. I do this about every 30 minutes. It's a bit annoying because 99.9999% of the time, the part will be asleep, so you'll have to wake it up to send the transaction that puts it in sleep mode.

I hope that helps. I wish I had known about it from the beginning!

[Fabian_R]

Hello, 

Thank you for using our products.

In our Datasheet, we provide the NFC and the I2C address. For setting the standby mode, in the session register please check section 8.1.3.19.

In this case, the NFC address is A8h. Where byte 0 provides the configuration, in this case, bits 3 to 6 should show 0111b for the standby mode.

In the datasheet, it is mentioned that only CONFIG bits only take effect after the next session (after POR).

In the Datasheet (Table 37. Configuration Definition) AUTO_STANDBY_MODE_EN: If the IC is operating normally, the standby mode is deactivated but, if there isn't an RF field present it enters standby mode.

This is also mentioned in section 8.3.5: "The IC will leave standby mode according to the configuration when NFC field is detected, automatically, or HPD pin gets pulled to HIGH for at least 20 µs and released again. In standby mode, the current is typically less than 6 µA."

Please let me know in which scenario are you having issues so I can provide a more specific answer.