Control N-MOSFET by GPIO alone?

[mmitchell]

Hi,

Can we control a N-Channel MOSFET directly with a GPIO pin without using another transistor?

The picture shows an example from OnSemi App Note Using MOSFETs in Load Switch Applications. Because V_GS needs to be positive (depending on the threshold), there is an additional VGATE and transistor used to control the gate voltage. When ENn is low, Q1 if off and VGATE is applied to N-MOSFET’s gate, making it open.



On the other hand, if we have GPIO which is much higher than VIN, as shown in the lower part:

VIN = 0.6V
GPIO = 1.8V​

Can we directly use GPIO to control voltage of G, thus saving a transistor?

The transistor we choose is Vishay Si2312BDS.

An additional question is about Diode Forward Voltage. Si2312 list diode forward voltage V_SD as 0.8V > 0.6V VIN. Could there still be any current passing through the transistor?

I suspect that that “Diode Forward Voltage” is measured when V_GS is zero, therefore is irrelevant to our configuration. Is it correct?


Matt

 

[FvM]

Diode forward voltage is irrelevant for your application because Vds will be always positive, so the substrate diode is reverse biased.

With Vin = 0.6V, you get Vgs of only 1.2 V. It will be typically sufficient, but the datasheet doesn't specify a maximum Rdson.

 

[mmitchell]

FvM,

Would it work if I apply PWM signal at the GPIO, so ultimately the load gets a further divided-down (in terms of power) output as compared to the original 0.6V ?