NT3H2111 VOUT Max Capacitance

[mike_durian]

The NT3H2111 datasheet lists a "total connected capacitor" range of "150 nF up to 220 nF maximum". Is the 0.22uF max a hard limit? I'd like to run the energy harvest output through a LDO to provide a normalized voltage with multiple possible voltage sources (VOUT from the HT3H2111, power from a debug/programming probe). The LDO requires a 1uF input cap, which exceeds the 0.22uF limit.

Even if I didn't use an LDO, the combined decoupling caps on the microcontroller will exceed the 0.22uF limit.

How do people deal with this limit? Or can it be safely ignored?

Thanks, mike

[mike_durian]

Hi @EduardoZamora ,

Thank you for the reply. So the 0.22uF limit is not a hard cap? You say a larger load will make it harder for the reader to wake up. Is there any documentation, charts, graphs, etc. that show the effect of load capacitance on system behavior (at different field strengths)?

How do people power MCUs and associated circuitry that require larger load capacitance?

[EduardoZamora]

Hi,

My apologies, the only information available regarding Energy Harvesting behavior is included in AN11578 Energy Harvesting with the NTAG I²C and NTAG I²C plus (considering a 220nF capacitor) and NTAG I2C plus Data Sheet, Chapter 8.6.

Perhaps you could consider a Diode to try to isolate a "local" capacitance; however, this out of my scope and it depends on your design. Please keep in mind that our recommendation is to use a total capacitance in the range of 150nF - 220nF for reliable operation, otherwise the proper functioning cannot be guaranteed. I apologize for the inconvenience.

Regards,
Eduardo.

[EduardoZamora]

Hello @mike_durian

Hope you are doing well.

As stated in the documentation, and as you mention, NXP recommends a storage capacitor in the range of 150nF to 220nF between VOUT and GND to ensure the voltage does not drop during modulation or application.

You should consider that the capacity connected to the energy harvesting pin should only be as large as needed by the external system – the larger the capacity is, the harder it is for the reader to wake up and supply the NTAG I²C.

Regards,
Eduardo.