Tool/software:
Looking at TI designs for F28P550XJ I see some differences between the design of the Control Card and the Launchpad on the Crystal Oscillator circuit.
On the Control Card the dampening resistor is shown to be connected on MCU_X2 (R92) which is defined as “Crystal oscillator output”, while on the Launchpad design is shown to be connected on GPIO19_X1 (R106), which is defined as “Crystal oscillator input”.
Moreover, in some other TI documents about the Hardware Design Guidelines the following PCB layout is recommended, where the dampening resistor (Rs) is connected on X2 path, as can be seen below:
The questions that arise here is where the dampening resistor should be connected, on X1 path or X2 path? How would the two different connections affect the clock signal going into the DSC and overall, the quality of the design?
Below you can see the crystal oscillator circuit for each design:
| Control Card design (from sprr500) | Launchpad Design (from sprr499) |
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Thanks!
