Part Number:FDC2214EVM
Hi,
I am testing FDC2214EVM, and have a few questions about its clock oscillators. Both the schematics and the physical board show it has two clock oscillators, Y1 and Y2. Y1 is a 24 MHz oscillator in the MSP430 microcontroller section and Y2 is a 40 MHz oscillator in the FDC section.
The user guide (section 2.7.2) has following description
2.7.2 Selecting the Clocking Source: While the device contains an internal oscillator which requires fewer components in a system, it is recommended to use an external oscillator for precision applications. The EVM includes a 40MHz oscillator on-board, but an external off board signal can be used.
I tried both the internal oscillator (43.4 MHz) and the external oscillator (40 MHz), the internal oscillator achieved ± 0.015 pF precision, while the external one achieved ± 0.002 pF, which is a significant improvement.
Here are my questions:
1. How is the 43.4 MHz derived from Y1 (24 MHz) and Y2 (40 MHz)? The 43.4 MHz shows in the configuration page. My understanding is that a sub-frequency can be derived using a divisor, resulting a sub-frequency lower than its base.
2. If the Y2 (40 MHz) is considered as an external oscillator, the internal one should be Y1 (24 MHz) in terms of the MSP430 MCU. I checked both specifications, Y1 (ABM8-24.000MHz-B2-T) has a frequency stability ± 20 ppm, while Y2 (625L3C040M00000) has a frequency stability ±50 ppm. Y2 is poorer than Y1 in frequency stability, which is not consistent with their actual performance. How to select a better oscillator as an external off board signal? can someone recommend an oscillator that outperforms Y2? Frequency range and stability, which one plays the most important rule?
Y1 (ABM8-24.000MHz-B2-T) link https://abracon.com/Resonators/abm8.pdf
Y2 (625L3C040M00000) link https://www.ctscorp.com/wp-content/uploads/2015/11/008-0329-0.pdf
3. I am going to use one MSP430 to control multiple FDC2212/2214, can Y1 be replaced with Y2 in the MSP430 section and eliminate all Y2s in the FDC sections?
Regards,
Gu