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This question may be stupid but how should I connect an unused FET in a dual-channel MOSFET ?

I using this one multiple times on my board but in one case I'm using only one MOSFET. I'd like to know how I should connect the unused one ? I guess I should connect the gate to the source (through a resistor) but what about the source pin ?

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Assuming you can't switch to a single MOSFET package which would probably be cheaper, you can simply terminate the pins.

Three options:

  1. If the source of the MOSFET you are using is grounded, then connect all three pins (Gate/Source/Drain) to ground (or even just gate and source). No need for any resistors.

  2. If the source of the other MOSFET is not grounded, connect the gate and source of the unused MOSFET both directly to the source of the used MOSFET. Again, no resistor required.

  3. Leave the pins floating, but with gate and source tied together.

There isn't much danger of anything conducting, as the circuit is not like digital inputs whereby you might get shoot through currents from floating inputs. Though keeping the gate and source tied together is no bad thing.

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    \$\begingroup\$ Switching to a single MOSFET for this one instance might not be cheaper due to the additional BOM line item... \$\endgroup\$ – ThreePhaseEel Aug 5 at 2:42
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enter image description here

  • Connect unused gate and source to 0 volts or
  • Connect source to 0 volts and gate to 0 volts via a 100 kohm resistor and
  • Leave drain unconnected

Instead of 0 volts, if it's inconvenient connect source to the same potential as the other source and gate the same or via the 100 kohm resistor.

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  • \$\begingroup\$ Hmmm... that schematic shows the bodies connected to the sources. Are the bodies electrically isolated? On a single piece of silicon, I would expect the body to be connected to the substrate, which gets interesting for two theoretically independent transistors. \$\endgroup\$ – d3jones Aug 5 at 14:29
  • \$\begingroup\$ @d3jones it's a good point and unfortunately the data sheet doesn't indicate yes or no. Neither does it indicate what the maximum voltage is between the two devices so, if you were looking for this information you'd have to contact NXP. \$\endgroup\$ – Andy aka Aug 5 at 15:26
  • \$\begingroup\$ Or you can just measure the resistance between the source terminals with everything else disconnected. If it's not open-circuit then you have a problem. \$\endgroup\$ – d3jones Aug 6 at 16:40
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There should be no issue with just leaving all pins floating. It's not like an op-amp that still gets power even when unused.

You could also just short all terminals to GND or whatever nearby rail you want.

Or, if your application allows, connect it in parallel with the other MOSFET so both are used.

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