FAQ_ How to choose a high-speed crystal for BlueNRG-x

nmg

FAQ_ How to choose a high-speed crystal for BlueNRG-x [Copy link]

 

Author of this article: Zhu Junwei, an engineer at ST

Click to download the pdf document to view: FAQ_ 如何为BlueNRG-x选择高速晶体 .pdf (376.03 KB, downloads: 0)

2019-11-29 20:13 上传

点击文件名下载附件

Keywords: BlueNRG-1/-2, crystal

Question: Some customers often ask us how to choose a high-speed crystal for BlueNRG-X?

Answer from ST engineer:

1. From page 144 of the specification, we can get the following information:

Characteristics measured over recommended operating conditions unless otherwise specified. Typical value are

referred to TA = 25 °C, VBAT = 3.0 V.

We recommend choosing a crystal with a maximum frequency deviation of +-20ppm at room temperature.

2. To achieve lower power operation and good frequency stability of the crystal, the crystal load capacitance C0 is considered as follows. The figure below shows a simplified block diagram of the amplitude controlled oscillator used in the BlueNRG family.

Low power consumption and fast startup time is achieved by choosing a quartz crystal with a low load capacitance C0. A reasonable choice for capacitor C0 is 15 pF. To achieve good frequency stability, the following equation needs to be satisfied:

Where C1’=C1+CPCB1+CPAD, C2’= C2+CPCB2+CPAD, where C1 and C2 are external (SMD) components, CPCB1 and CPCB2 are PCB routing parasites and CPAD is the equivalent small-signal pad-capacitance.

3. The following are some crystal models used by mass production customers for your reference:

1) Hele, X3S016000b91H for 16Mhz in MP customer;

2) Yoke,S2016A-032000-F08-BDD-1AXA for 32Mhz in MP customer;

3) Ndk, NX2016SA/EXS00A-CS06654 for 32Mhz in MP customer;

4) Ndk, NX3225SA -32.000MHz-EXS00A-CS05997 for 32MHZ in demo board;

5) Ndk, NX3225SA -16.000MHz-EXS00A-CS05997 for 16MHZ in demo board.