Placement/location of pull-up/pull-down resistor?

I have connected a microcontroller GPIO pin, which is intended to be an output, to a DC-DC converter's active high Enable input pin. Since this pin is active high, and because I do not want this converter to be ON at power up or before it is required, I have used a pull-down resistor on this line to keep it disabled.

I am slightly confused as to where should this pull down resistor be ideally placed. Should it be placed near the GPIO pin or the Enable pin?

Same question for pull-up resistor, in the case when Enable is active low and I have to use a pull up on the line.

• It doesn't really matter, but it may be clearer to place it close to the input it is pulling up or down. Nov 5, 2014 at 9:20
• Thanks for the reply. Its current location is near DC-DC converter's Enable pin, as you have mentioned. So I will leave it there. By the way, I think it is more of an "intuition" case rather than logical. I could be wrong though. Nov 5, 2014 at 9:43
• I find it difficult to imagine that it's going to make any real difference. A pullup resistor is typically on the order of 5-10K ohms. If we assume a 10% resistor, that means the tolerance is +/- 500-1K ohms. It would take a ridiculously long trace before you've change the resistance by even close to that amount. IOW, you could easily build the same circuit twice, and put one resistor next to the input pin, and the other as far away from it as possible, and one that's farther way could still (easily) have a "stronger" pull-up/down than the one that's closer. Nov 5, 2014 at 22:26
• Thanks for your inputs, Jerry. I understand you mean having two PU/PD on the signal, is it? Nov 12, 2014 at 5:36

• You can just think all the traces have some impedance, if you have a long trace to your pull-up, then the total pull-up will be $R_{p} + R_{trace}$, and if your pin has internal impedance $R_{in}$, the trace impedance will make the pull-up more weaker, that is, the voltage on your pin will be lower. Although the difference may be small. So, i always put PU/PD closer to the pins which need them. Nov 5, 2014 at 13:09