# Logic level MOSFET gate trace length

I am using a micro-controller to switch a logic level MOSFET (the IRLR3103). The output of the MCU is 3.3V. I have a 1K resistor in series with the gate as well as a 100K pull down resistor as close to the MOSFET gate pin as possible.

For my PCB layout I am focusing on keeping the drain (output) trace as short as possible but this means the gate trace from the MCU is as much as 150mm long in some cases. The gate traces are 0.6mm wide on 2oz/ft2 copper.

Does this layout sound reasonable or should I try another layout with shorter gate traces from the MCU?

Edit: I should add that the purpose of the MOSFET is to provide switching for things like cooling fans so high-frequency switching isn't a consideration.

• I believe that there will not be a problem if the MCU's corresponding pin is configured as push/pull (i.e. lowest output impedance possible). Feb 17, 2020 at 13:03
• Also, if the MCU pulls the gate low, will the pulldown really be necessary? Feb 17, 2020 at 13:49

If you expect noise interfering with the gate signal, next to @RohatKılıç comment to configure the pin as push/pull, make sure the gate resistor is closest to the mosfet.

Compare circuit A and B below(1).
On both cicuits noise is acting as represented by red arrows.
In circuit A, (assuming push/pull configuration) noise can hardly alter the gate signal because the uP pin is low impedant. Moreover, the noise will be attenuated by R1 and the gate capacitance. In circuit B, R1 is cancelling the benefit of the low impedant pin of the uP.

simulate this circuit – Schematic created using CircuitLab

(1) Although from a schematic view exactly identical, an attempt is made to show the physical location of the gate resistor.

I wouldn't expect any negative consequences of that length of trace.

A 150mm trace with a 0.6mm * 0.07 mm crosssection (for 2 oz/ft²) results in a resistance of around 0.06 Ohms - negligible, especially in comparison with your 1k Ohm series resistor.