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CLRC663 Datasheet(PDF) 50 Page - NXP Semiconductors |
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CLRC663 Datasheet(HTML) 50 Page - NXP Semiconductors |
50 / 132 page CLRC663 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved. Product data sheet COMPANY PUBLIC Rev. 3.3 — 3 April 2012 171133 50 of 132 NXP Semiconductors CLRC663 Contactless reader IC 8.8 Clock generation 8.8.1 Crystal oscillator The clock applied to the CLRC663 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 CLRC663 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 23 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 41 “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 32. Quartz connection Table 40. 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 CL load capacitance - 10 - pF Pxtal crystal power dissipation -50 100 W 001aam308 27.12 MHz XTAL1 XTAL2 READER IC |
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