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I'm working on a circuit implementing the TI CC2640R2F (Datasheet) which requires an external 24MHz crystal oscillator to function. In the schematic (pg. 42), it shows what looks like a normal oscillator symbol but with extra brackets and wires on it.
This is a clipping from the example schematic
Excuse the poor drawn in IC connections, pin designations are on pg. 10 and state that this X24M_N/P are "24-MHz crystal oscillator pin 1/2". I have 3 questions:
1. Why does the symbol look like this rather than the standard oscillator symbol
2. What are the four different pins?
3. Why does the oscillator right next to it in the schematic use the normal symbol?

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    \$\begingroup\$ Looks like a crystal with a guard ring. You wouldn't normally put the guard ring explicitly though; you'd expect the layout engineer to know what they're doing. \$\endgroup\$ – Ignacio Vazquez-Abrams Jun 23 '18 at 19:41
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    \$\begingroup\$ Could also be a grounded metallic case. Potentially the DNM (Do No Mount) indication on the caps is to do with the case offering load capacitance to the xtal? Who knows. Part-numbers and datasheets do, as well as principal engineers at TI. Well, hopefully the latter, not always a given in my experience. \$\endgroup\$ – Asmyldof Jun 23 '18 at 19:49
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This is one of the crystals in a flat metal can with four pins. Two of the pins connect to the crystal, and the other two to the can. Those last two should be connected to ground. The can then acts like a shield.

In your schematic, pins 1 and 3 are the crystal connections, and pins 2 and 4 connect to the can.

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  • \$\begingroup\$ Thanks for the answer, would you be able to tell me if a part such as Microchip's DSC6003CI2A-024.0000T (datasheet) Would be a suitable substitute for this crystal? If so, what would my connections be? Thanks! \$\endgroup\$ – Peake Jun 24 '18 at 17:28
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    \$\begingroup\$ There should be no need to substitute. Use the crystal you have and that's shown in the schematic. \$\endgroup\$ – Olin Lathrop Jun 24 '18 at 22:26
  • \$\begingroup\$ That's my problem. The only markings on that schematic is Y2 and 24MHz. The schematic came from a typical application section in a datasheet and provides no part number or specification. I'm having trouble finding a suitable component to use in my own design. if you have any suggestions for components I'd appreciate them. Thanks again! \$\endgroup\$ – Peake Jun 24 '18 at 22:30
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    \$\begingroup\$ @pea: Probably any parallel resonant 24 MHz crystal would work. \$\endgroup\$ – Olin Lathrop Jun 25 '18 at 10:44

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