StartUp Routine of NHS3152

[ingo_wuellner]

Hello Community,

we are observing a strange behavior on the startup Routine using the NHS3152TEMOADK. 

The setup is as follows:

The NHS3152TEMOADK Board is placed on an active ISO15693 reader(The reader /tag coupling is sufficient and the reader has an output power of 1W). The Coincell Battery is not plugged in, so Vbat is not available.

We then plug in VBat and observe the red LED on Pin 7. 

The Firmware does the following:

Pin 7 is set high as soon as VNFC gets available.

The automatic source selector is set to default, thus selects VNFC first and once the battery is plugged in, immediatly switches over to VBat.

We tried both with WakeOn enable and disabled.

The expected behavior is, that the LED will be powered by VNFC first and VBat as soon as the Battery is plugged in but we observe that the LED is on once VNFC is available and switches of as soon as we plug the battery in.

Interestingly we measure a voltage of 1V at the always on domain VAL_ON. 

This behavior does not match any of state machine and source selector behavior described in the datasheet. 

We seem to work around this, once we place a 400nF Capacitor in parallel to the NReset Pin.

Is this behavior intended or are we doing something wrong here?

Any help is strongly appreciated.

Best regards

Ingo 

[ingo_wuellner · Accepted solution]

Hi all,

sorry for replying on my own question, however we investigated the problem further and after testing with the devboard and checking the docs in the SDK we found the issue.

The NHS3152 enters the power off state once the battery is inserted (VBAT rising after VNFC is applied) and needs a field off - field on event (RF Reset) to leave this state and enter active state in case the battery is inserted while the system is in field.

From my perception, this behavior was not self explanatory from the datasheet, especially considering the state description in the datasheet on page pp. 13ff., maybe this could be described in more detail in a future revision of the datasheet or the user manual.

Thanks in advance for that!

Just wanted to tell this to anyone stumbling across this behavior as well.

Best regards

Ingo Wüllner