MFRC63002R datasheet(44/118 Pages) NXP

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MFRC630

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Product data sheet

COMPANY PUBLIC

Rev. 3.1 — 6 September 2012

227531

44 of 118

NXP Semiconductors

MFRC630

Contactless reader IC

8.8 Clock generation

8.8.1 Crystal oscillator

The clock applied to the MFRC630 acts as time basis for generation of the carrier sent out

at TX and for the quadrature mixer I and Q clock generation as well as for the coder and

decoder of the synchronous system. Therefore stability of the clock frequency is an

important factor for proper performance. To obtain highest performance, clock jitter has to

be as small as possible. This is best achieved by using the internal oscillator buffer with

the recommended circuitry.

8.8.2 IntegerN PLL clock line

The MFRC630 is able to provide a clock with configurable frequency at CLKOUT from

1 MHz to 24 MHz (PLL_Ctrl and PLL_DIV). There it can serve as a clock source to a

microcontroller which avoids the need of a second crystal oscillator in the reader system.

Clock source for the IntegerN-PLL is the 27.12 MHz crystal oscillator.

Two dividers are determining the output frequency. First a feedback integer-N divider

configures the VCO frequency to be N

 fin/2 (control signal pll_set_divfb). As supported

Feedback Divider Ratios are 23, 27 and 28, VCO frequencies can be

 fin / 2 (312 MHz), 27  fin / 2 (366 MHz) and 28  fin / 2 (380 MHz).

The VCO frequency is divided by a factor which is defined by the output divider

(pll_set_divout). Table 33 “Divider values for selected frequencies using the integerN PLL”

shows the accuracy achieved for various frequencies (integer multiples of 1 MHz and

some typical RS232 frequencies) and the divider ratios to be used. The register bit

ClkOutEn enables the clock at CLKOUT pin.

The following formula can be used to calculate the output frequency:

Fig 27. Quartz connection

Table 32.

Crystal requirements recommendations

Symbol

Parameter

Conditions

Min

Typ

max

Unit

fxtal

crystal frequency

27.12

MHz

f

xtal/fxtal

relative crystal

frequency variation

250

+250

ppm

ESR

equivalent series

resistance

-50

100



load capacitance

Pxtal

crystal power

dissipation

-50

100

W

001aam308

27.12 MHz

XTAL1

XTAL2

READER IC

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