I wanted to know if my schematic looks correct.
I am unsure if I have connected VCC and GND correctly with the capacitor.
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\$\begingroup\$ Please explain one thing first, are you asking about the correctness of the circuit design represented by the schematics, or about the correctness of the schematics representing the circuit? Also note that there may be many ways to draw the same connection, and how to draw it may be subject to personal or company preferences. \$\endgroup\$– JustmeCommented Apr 13, 2023 at 9:21
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\$\begingroup\$ Im just not 100% sure on the grounding stuff, if i should draw it like this or if i should add a separate ground point instead of looping it back in my drawing, trying to make it look neat and easy to read. \$\endgroup\$– fiven80440Commented Apr 13, 2023 at 9:39
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2 Answers
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- NOTE: CAN bus requires an impedence of 60ohm, meaning that the terminating resistor must be 120R not 120k!
- Since you are neither using standby or Vref features, you picked the wrong part. Go with SN65HVD232.
- The 100nF cap is fine and should be there, naturally as close to the Vcc pin as possible. As for how to draw proper schematics, the cap should be drawn vertically between 3V3 and GND. Never draw decoupling/bulk caps horizontally.
- I'd recommend placing a common mode filter on the CAN lines (examples).
- You'll need to explicitly specify the power rating for the 120R resistor. Some rule of thumb says 0.4W, but 0.25W is probably enough for most purposes. Just don't mount some tiny 0402 there.
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\$\begingroup\$ Thankyou for the info, When drawing my pcb, with my CanH should my track connect to the 120R 1st before it connects into SN65HVD232 or it does not matter? sorry for my silly questions, just trying to learn \$\endgroup\$ Commented Apr 13, 2023 at 10:30
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\$\begingroup\$ @fiven80440 It's such short distances that it won't matter. Though in case the 120R isn't mounted, it is good practice to keep the total stub length as short as possible. \$\endgroup\$– LundinCommented Apr 13, 2023 at 10:51
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1\$\begingroup\$ 1) 120k -> good find. 2) The SN65HVD232 doesn't support slope control. This schematic show that the transceiver is used in slope control mode. \$\endgroup\$– VelvetCommented Apr 13, 2023 at 10:53
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1\$\begingroup\$ @Velvel Ah yeah it is. However, my field experience of these transceivers is that if you want to use slope control for EMC purposes, you picked the wrong transceiver to begin with. The 5V ones have much better EMC characteristics and this one here is a relatively old part by now. \$\endgroup\$– LundinCommented Apr 13, 2023 at 10:57
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So you are simply asking which is a good way of drawing the capacitor ground connection.
Like I said it makes no difference how you draw it as it won't change the circuit.
You can wire it like that, or separate the ground, or separate it completely.
It is a personal preference how you want to draw it. Some people might even prefer to draw the capacitor separately further away from chip, by grouping all bypass caps into one corner, or separate page.
But one thing is sure, most people would rotate the capacitor so connections are vertically, right now it just looks weird.
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\$\begingroup\$ "Some people might even prefer to draw the capacitor separately further away from chip, by grouping all bypass caps into one corner" Those people are confused and likely from that old confused school of never drawing supply/ground to IC in a schematic either. Obviously the cap should be drawn close to the IC it is decoupling so one can swiftly tell what it does. Extra relevant when you have multiple supply planes but cheap out on cap by picking low voltage ratings (like you have 24V and 5V on board but decouple 5V IC with 16V rated caps - wouldn't want those on the 24V plane by mistake). \$\endgroup\$– LundinCommented Apr 13, 2023 at 9:58
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\$\begingroup\$ @Lundin It depends on the case too. I also hate if it is not immediately obvious if a chip has bypass or not. But in one case, I have a chip with ~28 positive supply pins for 4 different voltages, grouped to 14 separately filtered bypass groups (digital and analog supplies, core voltages and IO supplies, sensitive PLL filtering, grouped by internal functions), and there is a separate schematic symbol for supplies. I don't mind a bit that the 60 or so bypass caps are grouped into 14 clumps down at schematic corner near the chip power symbol. You can still see which pins have which caps. \$\endgroup\$– JustmeCommented Apr 13, 2023 at 10:54
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\$\begingroup\$ Having parts with some >100 pins as a single schematic symbol is often cumbersome. In such situations with big BGA or QFP parts, I prefer if the part is split into several schematic symbols. So you could have one part documenting PLL filtering and the oscillator, one documenting core voltage decoupling, one documenting some ADC peripheral supply etc etc. \$\endgroup\$– LundinCommented Apr 14, 2023 at 6:37