I built the "shield" board for relatively high speed on the mezzanine connectors (~50-60MHz signals) and discovered that the main board has actually 220 Ohm resistors in series with all pins. When I looked at schematics, the values were shown as 220 (which on SMD resistors mean 22 Ohm - pretty usual and benign value for series termination on traces). But measurement shows 220 Ohm and as the result, the design does not work. It is inconvenient to rework all boards (I have few) and replace these 0402 resistors with jumpers.
I am wondering what was the designers' train of thought when volume producing the boards which don't work with many practical signals?
Even if the idea was to protect the I/O pins, it was not a great idea as using this relatively decent high speed chip is not possible without rework of the board!
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DmDerev
I built the "shield" board for relatively high speed on the mezzanine connectors (~50-60MHz signals) and discovered that the main board has actually 220 Ohm resistors in series with all pins. When I looked at schematics, the values were shown as 220 (which on SMD resistors mean 22 Ohm - pretty usual and benign value for series termination on traces). But measurement shows 220 Ohm and as the result, the design does not work. It is inconvenient to rework all boards (I have few) and replace these 0402 resistors with jumpers.
I am wondering what was the designers' train of thought when volume producing the boards which don't work with many practical signals?
Even if the idea was to protect the I/O pins, it was not a great idea as using this relatively decent high speed chip is not possible without rework of the board!
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