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I was wondering if there is a difference between the following switch circuits:

enter image description here

enter image description here

I simulated these here and here and they both seem to have the same behavior. The one with two FETs was suggested in BQ25505 datasheet here as a switch to disconnect the load from the power management IC.

Is there any difference between their switching speed or power dissipation?

PS: I'd appreciate any suggestions regarding the choice of the FETs in terms of low power dissipation and fast speed. The source voltage is maximum 6V (max 500mA) and the gate voltage is minimum 3V.

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  • \$\begingroup\$ This is exactly like what was provided in the datasheet. \$\endgroup\$ – vmontazeri Jun 12 '18 at 3:06
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    \$\begingroup\$ M2 can prevent V6 from discharging into R12. If that is all you need, then the lower circuit is fine. But suppose R12 is a battery with a voltage higher than V6. In that case, M2 cannot prevent backflow of current from load into V6 because M2's intrinsic diode (body diode) will be forward biased in this condition. The state of the channel does not matter. But M4, when off, CAN prevent the discharge in that direction because its intrinsic diode will be reverse biased. \$\endgroup\$ – mkeith Jun 12 '18 at 3:34
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The first circuit that you show will work with bipolar or AC signals. The second circuit will not block the negative input signal when it is supposed to be OFF.

Try changing your simulation input signal source (V6) to AC and look at the output,

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  • \$\begingroup\$ Thanks! I'd also appreciate any suggestions regarding the choice of the FETs in terms of low power dissipation and fast speed. \$\endgroup\$ – vmontazeri Jun 12 '18 at 3:30
  • \$\begingroup\$ What voltage, what current, what is the magnitude of the gate drive signal? Please modify your question with this information. \$\endgroup\$ – Dwayne Reid Jun 12 '18 at 4:42
  • \$\begingroup\$ Added the information. \$\endgroup\$ – vmontazeri Jun 12 '18 at 4:53

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