NTP5332 in hard power down mode

[peter_n06]

Hello,

I am currently designing on a ultra-low power application where NFC can be used to access the application both when it is in deep sleep mode and in running mode. In deep sleep mode, we need the NFC tag to consume the less power possible and the hard power down mode of the NTP5332 seems promising in that matter. The idea is to set the NTP5332 in hard power down mode, and to wake it up only when an I2C access is necessary.

Nevertheless, when pulling HPD pin to Vcc, I’m not able to communicate with the tag through NFC anymore. I tried different smartphones and NFC readers without success. Also, on the OM2NTP5332 board (I use this for evaluation), there is a 10K pull-down resistor on HPD pin which adds power consumption when HPD is drive to 1.8V. I tried to remove this resistor, but result is the same (only power consumption is decreased).

Is it normal that NFC communication is not working anymore in hard power down mode ? Is the pull-down resistor mandatory on HPD pin ?

Best regards.

[peter_n06]

Thank you for you quick answer.

It looks like the HPD feature will not help me then, since I would like to be able to access the tag via NFC at any time. Also, I would like to be able to wake up my application when NFC is starting to talk, but from what I’ve tested, it looks like that ED pin is not working when in HPD mode either. Is it correct ?

My backup solution may be standby mode. Consumption is higher, but probably still low enough for my needs. However, I’m confused about how to use this mode from the I2C master standpoint. Datasheet says I should pull HPD high for at least 20us then release it to exit standby. But if I set AUTO_STANDBY_MODE_EN=1 in CONFIG_0, the tag automatically returns in standby mode when HPD is released.

Is there a way to control enter/exit from standby mode from I2C standpoint? Or can it be managed only from NFC side ?

Thanks & Best regards

[fangfang · Accepted solution]

Hello,

In HPD mode IC is switched off, neither of interfaces is available (wired or NFC). it is not recommended to connect HPD always to VCC, it should rather be connected to an MCU or external circuitry which determines whether or not to send that NTAG5 to HPD.

A 10k resistor is connected to GND on SW1 as the schematic of the board. The function of this resistor is to shunt. Once SW1 is closed, VCC will be loaded on HPD. It can shunt HPD. As soon as SW1 is released, 10K lowers HPD. And IC exit HPD mode.

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