Product data

Product data sheet

COMPANY PUBLIC

Rev. 3.3 — 4 February 2014

227433 47 of 120

NXP Semiconductors

MFRC631

High performance ISO/IEC 14443 A/B reader solution

out

= 13.56 MHz  PLLDiv_FB /PLLDiv_Out

8.8.3 Low Frequency Oscillator (LFO)

The Low-Frequency (LFO) is implemented to drive a wake-up counter (WUC). This wakes

up the system in regular time intervals and eases the design of a reader that is regularly

polling for card presence or implements a low-power card detection.

The LFO is trimmed during production to run at 16 Khz. Unless a high accuracy of the

LFO is required by the application and the device is operated in an environment with

changing ambient temperatures, trimming of the LFO is not required. For a typical

application making use of the LFO for wake up from power down, the trim value set during

production can be used. Optional trimming to achieve a higher accuracy of the 16 Khz

LFO clock is supported by a digital state machine which compares LFO-clock to a

reference clock. As reference clockfrequency the 13.56 MHz crystal clock is available.

Table 35. Divider values for selected frequencies using the integerN PLL

Frequency [MHz] 4 6 8 10 12 20 24 1.8432 3.6864

PLLDiv_FB 2327232823282328 28

PLLDiv_Out 78 61 39 38 26 19 16 206 103

accuracy [%] 0.04 0.03 0.04 0.08 0.04 0.08 0.04 0.01 0.01