Driving a high-side mosfet as a switch for a DC application

[niehu3s]

TL;DR: The most broke college student needs to drive a high-side MOSFET that will replace a relay, being ON for a long period. What is your suggestion?

Hi, I'm developing an open-source automotive Power Distribution Module for my undergraduate thesis. Briefly, a PDM replaces the relay/fusebox of a car with solid-state switches and current sensing, thus providing real-time diagnostics, the ability to interface with CAN Bus directly and enables to customize the behavior of the power distribution by code.

eg: https://www.ecumaster.com/products/pmu/ ; https://www.holley.com/products/data_acquisition/power_distribution_modules/

As a proof of concept, the PDM will have 4 12V/20A and 4 12V/10A channels. Each channel is made up of: a high-side current sensing amplifier and its shunt resistor; a N-Channel Mosfet and its high-side gate driver. As shown in the image below, where GATE_LC0 is the signal coming out of a STM32 BluePill:



However, I'm a broke (and Brazilian, which means everything is expensive) and can't seem to find a way to cheaply implement this gate-driver. There are ICs like the LTC1155, which are 2 Ch. high-side gate drivers, however they cost 6 dollars each, and I make only 95 dollars a month working a part-time job, so you can see how significant 30 dollars just in gate drivers would be XD.
 
Thus, my question is: What is your suggestion on how to drive 8 high-side NMOS cheaply? Remembering that it won't be used with high frequency switching and more like a conventional relay, staying ON for a long period.

[Doctorandus_P]

One way is to use an P-channel fet. Then you can just pull the gate to GND (if the max Ugs allows that).

Another way is to build a charge pump from a few diodes and capacitors that can lift the gate above the power supply voltage. In a more "advanced" form the MOSfet itself is made part of the charge pump, and this is called "bootstrapping". With that magic word you can find many examples. This is one of them:

https://www.malabdali.com/mosfet-bootstrap-for-high-side-driver/

Yet another way is to use a small auxiliary power source and "stack that on top" of your power supply. You will still need some kind of level converter to get upto that higher voltage.