NXP Semiconductors
AN11740
PN5180 Antenna design
AN11740
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Application note
COMPANY PUBLIC
Rev. 1.1 — 19 June 2018
345311
23 of 62
circuitry and those connected to the crystal. Those capacitors CXx, CAntx, C0x, C1x and
C2x must be NP0.
The inductor L0x must be capable of driving the required power: In case the maximum
output power is needed, the L0x must be able to drive the 200mA without going into
saturation.
Note:
Be aware of tolerances! The most critical tolerance in the antenna circuits
appears at the antenna coil itself, but even for the matching circuitry tolerances
of < ±1% are recommended.
4.1 PN5180 requirements
The PN5180 is optimized to support the EMVCo operating volume. Therefore, the Tx
output can drive up to ITVDD = 250mA. Based on a power supply voltage VBAT = TVDD
= 5V that means a possible total power consumption for the total antenna circuit of up to
P
tot
> 1W.
The power supply must be designed properly to be able to deliver a clean supply voltage.
Note:
Every noise level on top of the supply voltage can disturb the performance of the
PN5180. Therefore, sometimes higher values of the block capacitors in the range
of up to 10µF might help to improve the performance.
The PN5180 provides an NMOS/NMOS Push-Pull output stage to drive the antenna
circuit. The output impedance of each Tx outputs is approximately 1…3 Ohm (with
maximum GSN settings), so basically the antenna impedance itself controls the ITVDD,
and therefor the field strength.
The Fig 20 shows the driver current ITVDD versus the antenna impedance. The target
impedance to get a maximum field strength and power transfer should be close to 20Ω.
