AN4630 datasheet(29/33 Pages) STMICROELECTRONICS

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AN4630

Design recommendations when using

WLCSP34 package

The high-frequency crystal has to be put as far as possible from the matching network. The

tracks that connect the crystal pins to the BlueNRG FXTAL0 and FXTAL1 pins have to be

routed as far as possible from the matching network, and also have to be kept as far as

possible one from each other. The INNER2 layer has to be used to connect the crystal pins

to the BlueNRG FXTAL0 and FXTAL1 pins. The INNER2 layer has to be keeping empty

under the crystal. All these recommendations are shown in Figure 26: "High-frequency

crystal connection".

Figure 26: High-frequency crystal connection

The low-frequency crystal has to be put as far as possible from the matching network. The

tracks that connect the crystal pins to the BlueNRG SXTAL0 and SXTAL1 pins have to be

routed as far as possible from the matching network, and also have to be kept as far as

possible one from each other. The INNER2 layer has to be used to connect the crystal pins

to the BlueNRG FXTAL0 and FXTAL1 pins. The INNER2 layer has to be keeping empty

under the crystal. All these recommendations are shown in Figure 27: "Low-frequency

crystal connection".

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AN4630 Datasheet(PDF) 29 Page - STMicroelectronics