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# Tag Info

12

A schematic is not meant to be a drawing of a circuit, and shouldn't be used that way. The "pins" in a schematic just show connections. Put them wherever they need to go to make the drawing understandable, and don't worry about what they convey physically.

11

I'll start by answering your second question. Generally you should place pins in your schematic symbol so that it produces the neatest schematic possible. Usually this means power on the top, ground on the bottom, inputs on the left, and outputs on the right. I generally place the pin for the bottom pad logically based on its function. 9 times out of 10 ...

3

The style used for creating documentation depends upon the goal of the drawing. When I create a "Schematic", I try to make the drawing useful for Troubleshooting and understanding the function; Visual likeness to reality is intentionally not part of my thinking. When drawing a "Wiring diagram", more thought goes into making the physical reality clear, ...

2

It may be tempting to put pins in the same order as they are on the package. After all, it makes it easier to compare the schematic and the PCB. But there is a significant danger of mistakes. Especially voltage supply pins are usually spread on all sides of the package, and may not follow any clear order. Then when you are connecting them in schematic, ...

2

The data sheet you referenced essentially answers the question, if you look at figures 3.1, 3.2, 3.3, and 7.2. Organize your complete circuit diagram in a similar way, though (obviously) you don't need to draw the internal architecture of the chip. This is analogous to the simpler case of drawing a transistor or FET. You use a conventional symbol, without ...

1

For you to need to consider high-speed design (controlled impedance) rules you would need traces on your PCB that are physically longer than the wavelength/10 of the highest frequency component of your signal. For continuous wave RF (and long-pulse RF waveforms) this will correspond to: $$L \ge\frac{\lambda}{10}$$ For digital waveforms the rule of thumb ...

1

If you have a vacuum-tube computer with 100 nanosecond edges, then 10nanoSec or 20nanoSec round trip delays and reflections will be hidden in the edge waveform. In that case, your computer can be 5 feet across (5 + 5 nanosecond round trip) to 10 feet across (10 + 10 nanosecond round trip). This vacuum-tube computer will have UGLY waveforms (lots of ...

1

If your rise/fall time is much longer than the signal propagation time over the length of your traces, you're good to "get away without special PCB layout". So, basically, have a short traces and slow rise times. there are no special thresholds: the physics is always the same, it's just that at certain conditions you'll see some effects more strongly. Some ...

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