I'm currently working on a project based around the NHS3100 and the example code dp_tlogger.
The data is being logged no problem but retrieving the data creates a drop in the supply voltage. This drop is sometimes sufficient to be logged as a "battery depleted" message and therefore stopping all future measurements.
This behaviour is similar on the NHS3100 dev board.
We are looking for a solution on how we can actually use the NFC field as a power source when retrieving the data, instead of using the battery (3V CR1225).
Is there any application example?
To be clear:
Is this summary correct?
Thank you both for your replies.
Here is what we are doing and the problem:
Now the problems:
We appreciate that the battery voltage dropping is due to the battery (CR1225) having a high internal resistance. But we would like to be able to use the NFC field as a power source while reading the data out - so to stop pulling power from the battery, and stop this erroneous "battery depleted" message state happening.
We can't find any example application of the "Chip_PMU_Switch_OpenVDDBat" which we think could do the trick. The current dev board reacts the same way as our custom device.
We are also wary of using this function because if we lose the NFC field while the data is being accessed, and the VBAT is being disconnected, we might lose power completely to the device and need to reset the configuration anyway.
Do you have any working examples of the switching between VBAT and NFC field?
Ok. Thanks for the insights.
Some general remarks:
Thank you for your message. Here is an update on the progress:
We log data on the NHS3100 while being battery operated. Once in a while, we bring it to an NFC field to download the data. Once coming out of the NFC field, we carry on logging data.
In the firmware, therefore, we want to go from Battery to NFC field for the source of power, and then go from the NFC field to Battery power.
We got the transition from NFC field to Battery power working, but we can't get the transition from Battery to NFC field to work... The voltage drops too much and triggers a Brown out...
We added 2x220nF capacitors on PIO03 and PIO07.
The oscilloscope screenshot shows the voltage dropping when transitioning from 3.3V to NFC field.
Ch1: PIO0_3 voltage - Ch3: GPIO set when forcing VNFC
I have attached the snippet of code in the Execute loop. It controls the GPIO (which should be at 1 for 60ms, then changes back to 0):
We would hope that there is a way to transition from the Battery to NFC field without triggering a BOD. Can you please confirm? And guide us on how to do this?
A brown-out is easily reached when running on NFC.Did you try to reduce the load to the absolute minimum? Or are you talking about a reset?
My best recommendation is to try to avoid this trick, and run on battery continuously.
1. When the current is not enough, the power supply voltage will drop.
Therefore, the situation you are encountering is caused by insufficient power supply current.
2. About using NFC FILED to supply power to NHS3100
In fact, it is difficult for you to use the filed of the reader antenna to provide power to the NHS3100. As long as you check the NHS3100 datasheet, you can know the current required by the NHS3100 when it is running. Please see: Table 17. Static characteristics.
Assuming that the filed of the NFC reader antenna can provide power to the NHS3100, the NFC reader antenna must be specially designed, but we do not have a similar solution to provide customers.
Have a nice day!