NXP Semiconductors
AN11740
PN5180 Antenna design
AN11740
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2018. All rights reserved.
Application note
COMPANY PUBLIC
Rev. 1.1 — 19 June 2018
345311
38 of 62
(1) This impedance is measured unloaded.
Fig 33. Final tuning measurement result
4.2.2 Loading effect
The target impedance of the antenna design defines the ITVDD (driver current of the
PN5180) and the output power (i.e. operating distance for a given antenna coil) as shown
in section 3.
The lower the impedance gets, the higher the ITVDD becomes. Especially for high power
reader design, where the impedance is quite low to achieve a maximum of field strength
(as e.g. shown in Fig 7), the ITVDD might get close to its limit. In worst case loading
conditions, the ITVDD might even exceed the specification limits and therefor reduce the
life time of the PN5180.
So, in any case it is strongly recommended to check the loading and detuning of the
antenna.
The first step is to check two typical and extreme use cases:
1. Loading with Reference PICCs
2. Loading with a metal plate
Both cases must be tested under real operating conditions to ensure the ITVDD limit
(“active” loading, see section 4.2.2.3), but it is very helpful to check the “passive” loading
and understand its behavior.
4.2.2.1 “Passive” loading with ReferencePICCs
The loading with ReferencePICCs being calibrated for the Hmin test show a kind of worst
case loading with typical PICCs, since this is the purpose of calibrated Reference PICCs.
The Fig 34 shows the unloaded impedance curve (blue) as well as the loaded curve
(green), when the antenna is loaded with a ReferencePICC. In this case the Reference
PICC is place closely to the antenna to achieve the maximum possible coupling between
PCD and PICC.
