PCB trace width question

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alexandros

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Hi all,
I'm designing a PCB with some I2C ICs. I'm designing rather thick traces for the I2C communication (0.35mm), but I have a question concerning the following schematic:
teensy_forum_trace_width_question.png
All other traces are at 0.25mm width, and I was wondering whether the VDD trace should also be at 0.35mm, as it is connected to both I2C signals over resistors. Will connecting a 0.25mm trace through a resistor to the I2C signals increase impedance? Or it is fine to keep the VDD trace at 0.25mm? That might be pretty obvious to people who know circuit design, but it's not obvious at all to me.

Any hint appreciated
 
I’m still early on with my PCB design learning but for pull-up resistors the impedance is likely negligible, considering resistors aren’t exactly perfect it should be ok.

Though looking at the schematic you have VDD connected to ADDR and GND connected to ADDR through a resistor. What exactly are you trying to do there, the resistor to GND is not doing anything but generating heat in this case.
 
I’m still early on with my PCB design learning but for pull-up resistors the impedance is likely negligible, considering resistors aren’t exactly perfect it should be ok.

Though looking at the schematic you have VDD connected to ADDR and GND connected to ADDR through a resistor. What exactly are you trying to do there, the resistor to GND is not doing anything but generating heat in this case.
Thanks! Well, I'm trying to reproduce the circuit of the ADS1115 breakout by Adafruit. I guess the ADDR pin has a pull-down resistor to avoid floating if it's not connected, right? I could just ignore it altogether and simply connect ADDR to VDD, or am I getting this wrong?
 
I guess the ADDR pin has a pull-down resistor to avoid floating if it's not connected, right?
As far as I can tell from the datasheet, the ADDR pin cannot be left floating; it needs to be connected to a certain level:

Capture.PNG

If you want to reproduce the circuit of the ADS1115 breakout, connect ADDR to GND [with or without resistor].

Paul
 
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