[PN7462] CT-Charge pump heavily disturbes CL-RX-frontend

[johannesdev]

Hi!

The PN7462 uses a DC-DC converter (charge pump) for supplying a class A card on the CT-interface with 5V. We found that this charge pump can heavily disturb the PN7462's CL RX frontend even when powering light loads. I.e., when a CT class A card draws more than 10mA supply current practically every communication fails on the CL frontend.

This behavior can also be reproduced using the PN7462 eval kit!

Thus my question: can we somehow omit the charge pump and support class A cards? E.g., by supplying 5.5V±5% to pin VUP (#50 on the PN7462)? Would such a measure be compatible with class B and C cards as well?

[Kan_Li]

Hi @johannesdev ,

Actually we haven't heard of such kind of issue before, so is it possible to share the code you used for reproduce this issue on the PN7462 eval kit? Is it PNEV7462C? We may also reproduce this issue here and try to analyze the cause.

Have a great day,
Kan

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[johannesdev · Accepted solution]

The charge-pump can be disabled by using the bit DCDC_OFF (bit 13) within the register PCR_PMU_REG as Kan Li told be via a support case. In this case the Smarcard-LDO must be supplied externally via VUP.

Regarding the relationship of NFC and the charge-pump I did not get any answer back from NXP.

[AlexanderB]

Hello @johannesdev ,

this is under investigation and I hope to answer it within this week. 

Best regards,
Alexander