NAC1080 and NAC1081 Maximum harvesting power

[Almonleo]

Hi

In application NFC passive lock implementation with NAC1080 (infineon.com), it is mentioned that the with different mobiles and antennas, it is possible to get 10mW-40mW. However, we could not find in the datasheet the maximum power harvesting the NAC1080 and NCA1081 can get in passive mode, when running at its maximum 10 A/m field strength.

The datasheet explains that VCC_HB can be used as Input/ Output. Output mode is used in passive mode and a capacitor needs to be connected. However, no explanation is given about the maximum current the chip could deliver under the max field strenght conditions. 

Does anybody knows?

Thanks 

[Kanahaiya_K · Accepted solution]

Hello @Almonleo ,

NFC tag side controllers NAC1080 can be operated in two modes i.e. Active mode and passive mode. The load will be connected across the pin M_A and M_B . These loads will be operated thorugh the H-bridge converter internally.
These pins can supply the maxium current of 250mA between the M_A and M_B at the maximum voltage of 3.6 volts.
Please refer to the table-8 of the datasheet for the more details.

Please take a note that the nominal voltage across the capacitor C_HB can be increased by using the Boost converters and then reducing back to the nominal voltage of 3.3 volts by buck converters to match the required energy demand at the load side.In this way, more energy can be stored to the capacitor C_HB .Refer to the section 2.2 of the attached application note for more details.

Regards,
Kanahaiya

[Almonleo]

Kanahaiya,

The 250mA is the rating for the Hbridge. We are asking about the rating of the power harvesting section.

We want to know the maximum output current from pin VCC_HB when in passive mode. Please assume 10A/m. Basically we want to know how much power this chip can harvest.

[Almonleo]

Hi Kanahaiya

Thank you for your response. Unfortunately, that does not answer our question.

The 250mA is the current rating of the H-bridge (pins M_A and M_B). That is different from the maximum output current from pin VCC_HB when in passive mode.

We would like to know what is the maximum current pin VCC_HB will put out in passive mode when the external field is 10A/m ( you can assume an idea Class 1 antenna if you need one). Basically, we are trying to determine how fast a capacitor will charge, as well as the maximum power harvesting capabilities. That is different from how much load the h-bridge can drive.

Let us know if that helps and if you know the answer.

Best

[Kanahaiya_K]

Hello @Almonleo ,

The maximum harvested energy  depends on the capacitor and the voltage. The voltage is more or less fixed: 3.3V The rate of energy harvesting depends on the power of the transmitter, on the coupling between antennas of transmitter and receiver and on the distance between the antennas.

The maximum power which was estimated on the receiver (tag) side with the use of one of the mobile phones was 70mW. So the current on VCC_HB is correspondingly ~20mA (at voltage 3.3V).

Regards,
Kanahaiya

[Almonleo]

Hi @Kanahaiya_K 

Thank you for the replay.

We understand all the factors that affect the energy harvesting. My question is more about the limits of the chip. The datasheet for the NCA1080 and 1081 specifies a max H of 10A/m.

Assuming 10A/m is the field strength at the receiver's antenna, and we are using a class1 antenna (the largest NFC std allows), how much current will the VCC_HB be able to output continuously?

For our application, we are not planning to use a smart phone, but something that can put out a stronger signal so we can harvest more power and charge quicker. At this point we need to know how much current the VCC_HB can output without damaging it.

Maybe you know of other limiting factor to the power harvesting that could damage the chip

Thanks

Alex

[Almonleo]

Hi @Kanahaiya_K 

Did you have the chance to find out the maximum current the chip can put out in Vcc_hb based on the H=10A/m, ratings?

We are assuming the diode rectifier is the limiting factor, but we are sure.

Thanks

Alex

[Kanahaiya_K]

Hi Almonleo,

The maximum current that can be supplied at Vcc_HB is 250mA. The maximum voltage across the VCC_HB is 3.6 Volts. We can harvest all the energy from a field that has a strength of 10A/m. How much that is has to do with the coupling/matching between the receiver and the transmitter. It's between 20mA and 100mA." From that we can say the maximum power we could harvest is around 200mW, but that might be a bit far fetched.  We can quote 180mW. 

Regards,
Kanahaiya