Comparing two high side power switches

[Hawaslsh]

Hello all,

AP2191 p-channel
BD2268 n-channel
Sorry if this is a simple question. I am evaluating a few parts for a project where I needed a high side power distribution switch. The switch will be powering a VCO+PLL chip, LMX2820. The specs for the two parts are virtually identical except for the output type; one is an n-channel and the other p-channel. In my understanding p-channel FETS are usually used in high side switches, and typically P-MOS parts are slower and have higher on-state resistances as compared to N-MOS. However, clearly the P-MOS transistor is sized to match the on-state resistance of the N-MOS part. In my application I am not worried about switching speed, I simply need to follow a proper power-on sequence, is there a functional difference between the two parts, and is there a reason one would choose one over the other (besides cost, of course)?
Thanks in advance!

 

[stenzer]

Hi,

is there a functional difference between the two parts,

the significant difference is the usage of a charge pump by the N-channel MOSFET. To be able to use a N-type MOSFET as a High-Side-Switch (HSS), you need a voltage which is larger than the voltage you want to switch (applied to the drain) plus the gate-source voltage required to drive sufficient current while offering a low on-resistance. So the voltage at the gate has to be higher than the voltage applied at the drain to turn the MOSFET on. The block diagramm of your linked N-type HSS shows a charge pump.

The P-type MOSFET ist turned off when the source (connected to the voltage you want to turn on/off) and gate voltage are identical, and it is turned on when the gate voltage is lower than the source voltage. For most applications the gate of an ordinary P-cahnnel MOSFET is pulled towards ground by means of an additional N-MOSFET (the gate source voltage difference of the P-MOSFET should usually not exceed 20 V).

So by using an ordinary P-MOSFET or N-MOSFET, the P-type is much easier to control as it only needs an additional N-channel MOSFET (or open drain pin of an MCU, for low voltage applications), while the N-MOSFET high side switch requires a charge pump or a higher DC system voltage e.g. 12 V which is already present in your system to switch off e.g. 5 V.

BR