NFC is unstable when DCDEN1 is enabled.

[Brad Roberts]

I am using nRF52840 DK on VDD_HV. SW9 (nRF power source) set to USB and I am connecting a USB cable to J3 (nRF USB). SW6 is also set to nRF Only. My IC revision is QIAAD0.

In an effort to further reduce current consumption, I have recently tried to enable DCDEN0 with a REGOUT0 setting of 3V0. This works well. However, if I enable DCDEN1 the NFC communication becomes unstable. The FDT is no longer accurate and sometimes ends us in a timeout NAK. I could see the FDT errors in my NFC sniffer. Setting DCDEN1 back to 0x00000000 makes the problem go away but it consumes more power.

I checked the errata documents and I am not sure if this is related to

[218] NFCT: Frame delay timing is too short after SLP_REQ

I suspect that maybe enabling DCDEN1 has a crippling effect on TIMER4?

My firmware does not use a soft device. It is based on the NFC Tag text example from SDK 16.0.0, but I imported a customized hal_t2t.c from sdk 15.2.0 instead of using the precompiled lib.

I have tested this anomaly on 12 different nfc readers and my firmware becomes unusable on 5 readers which possibly have stricter timing constrainsts.

So my question is: How can I use DCDEN1 without affecting NFC FDT?

Best Regards

[Brad Roberts]

Peripherals used:

SPIM3 @ 32Mhz (NRF_SPIM_FREQ_32M)

WDT @ NRF_WDT->CRV    = 3 * 32768 ; // 3 sec. timeout

NVMC

app_timer

bsp_board_init(BSP_INIT_LEDS);

bsp_board_init(BSP_INIT_BUTTONS);

while (1)
{
    NRF_LOG_FLUSH();
    NRF_WDT->RR[0] = WDT_RR_RR_Reload; //Reload watchdog register 0
    power_manage();

}