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| High side switch |
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| Matt74:
Hello, I need a high side switch to power ON/OFF a sub-circuit (to save power, it runs on battery) and I was wondering what would be the advantages/drawbacks of using : an N-channel Mosfet (DMN2005LP4K-7) with a driver (LTC1981) versus a P-channel MOSFET (PMF170XP,115) connected directly to the microcontroller output (nRF52) * There is only one voltage rail available (2.8V). That would be the voltage at the gate and at the source (hence the need for a driver in the N configuration) * The load is very low, Id does not exceed 5mA * The switching freqency is very low (ON for 200us every 20ms) I'll post a schematics as soon as get my ECAD software to work again... Thanks ! |
| mjs:
N-MOSFETs have typically better performance for high load currents or voltages. Or you might want to prevent some power sequencing faults. If you can find P-MOSFET with suitable Vgs and Idss(off), go with that. |
| GeorgeOfTheJungle:
I use these very often (SK2301AA1SHB) driven directly by a gpio: https://lcsc.com/products/MOSFET_381.html?q=a1shb https://datasheet.lcsc.com/szlcsc/SK-SK2301AA1SHB_C118153.pdf |
| magic:
PMOS has higher RDS(on) so the load will see lower voltage when it's switched on. For example, 2Ω RDS(on) will make your 2.8V supply 2.79V when 5mA is drawn from it, but 1Ω would make it only 2.795V. NMOS requires a complex driver which consumes power, board space and $$. With only 5mA of load current the choice is obvious ;) |
| IgorIgor1233123:
you dont need complicated electronics, in most cases you can just use a voltage pump thats only a view small components, also today you have everywhere microcontrollers so you can create the square wave directly. So really not difficult or expensive. But yes for 5mA there is no reason not to use a P Channel |
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