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[#1]

When the PN7160 is set to LPCD mode, it cannot be activated from LPCD mode using a 2×2 cm antenna

Using the “NFC Antenna Tool,” we designed a 2 cm × 2 cm on-board antenna for the PN7160 with a Q-factor of 20 and a target impedance of 11 Ω. Since this is a small antenna, we enabled the PN7160's DPC in accordance with the “PN7160 Frequently Asked Questions [AN13892].”

Under these conditions, if we do not enable the PN7160’s LPCD mode, the two PN7160 devices can communicate normally via P2P. However, if we enable the PN7160’s LPCD mode, the PN7160 will be unable to wake up from LPCD mode. Using the same driver, however, we can activate it from LPCD mode with a 2cm × 4cm antenna.

The LPCD TRACE messages from 2 cm × 2 cm antenna are:
D (6358097) PN7160_I2C: NCI << 0x6f 0x13 0x04 0x80 0x83 0x80 0x03
D (6358597) PN7160_I2C: NCI << 0x6f 0x13 0x04 0x80 0x83 0x80 0x03
D (6359107) PN7160_I2C: NCI << 0x6f 0x13 0x04 0x80 0x83 0x80 0x03
D (6359617) PN7160_I2C: NCI << 0x6f 0x13 0x04 0x80 0x83 0x80 0x03

Please refer to the attachment for the antenna design parameters.
And the CORE_SET_CONFIG_CMD is set to :
uint8_t NxpNci_CORE_CONF_EXTN[]={0x20, 0x02, 0x6B, 0x05, /* CORE_SET_CONFIG_CMD */
0xA0, 0x40, 0x01, 0x81,    /* TAG_DETECTOR_CFG */
0xA0, 0x41, 0x01, 0x10,     /* TAG_DETECTOR_THRESHOLD_CFG */
0xA0, 0x42, 0x01, 0x0F,   /* TAG_DETECTOR_PERIOD_CFG */
0xA0, 0x43, 0x01, 0x00,   /* TAG_DETECTOR_FALLBACK_CNT_CFG */
0xA0, 0x0B, 0x57, 0xE5, 0x05, 0x90, 0x6E, 0x0F, 0x4E, /* DPC_CONFIG*/
0x00, 0x40, 0x95, 0xB7, 0xAA, 0x40, 0x9F, 0xA7, 0x99,
0x53, 0x9F, 0x97, 0x99, 0x5D, 0x9F, 0x97, 0x99, 0x5F,
0x9F, 0x97, 0x00, 0x68, 0x9F, 0x07, 0x00, 0x6A, 0x1F,
0x07, 0x00, 0x74, 0x1F, 0x07, 0x00, 0x78, 0x1F, 0x07,
0x00, 0x7F, 0x1F, 0x07, 0x00, 0x81, 0x1F, 0x07, 0x00,
0x8B, 0x1F, 0x04, 0x00, 0x8C, 0x1F, 0x04, 0x00, 0x96,
0x1F, 0x04, 0x00, 0x98, 0x1F, 0x04, 0x00, 0xA1, 0x1F,
0x02, 0x00, 0xA9, 0x1F, 0x00, 0x00, 0xAF, 0x1F, 0x00,
0x00, 0xB8, 0x1F, 0x00, 0x00, 0xC2, 0x1F, 0x00, 0x00
};
Is this issue caused by antenna matching or by the register settings?

Re: When the PN7160 is set to LPCD mode, it cannot be activated from LPCD mode using a 2×2 cm antenn

Hello, thank you for your interest in our products.

There are some limitations with your setup that I would like to address.

Even though the 2x2cm antenna can be implemented is recommended to attempt using a slightly bigger antenna size.

I would also like to clarify that P2P isn't recommended by NFC Forum, we highly recommend using HCE and Read/Write Mode instead.

It is very possible that the antenna size of the initiator could be too small to cause a detuning of the target.

Have you attempted waking up the Reader from LPCD with a regular PICC like a card? What is the result of this?

Please share the Smith cart and schematics of your prototype for further review.

Re: When the PN7160 is set to LPCD mode, it cannot be activated from LPCD mode using a 2×2 cm antenn

Have you been able to measure the impedance of your antenna?
It seems to be relatively low.