This question is about a personal project and related to my previous question but focusing on different issues or questions. By increasing the shunt resistor from 1 mOhm to 330 mOhm I wanted to avoid using a special amplifier like in my previous question.
A uC's PWM output will control 2A to 6A current through a heating-wire and since the resistance might change, the current value roughly will be fed back to ADC of the uC for regulation ect. The circuit will be soldered on a perfboard.
For minimalism, I decided to use a single-supply op amp and low-side sensing to avoid common-mode-voltage related issues.
For clarity I will write down the questions one by one in detail:
1-) This article examines the use of op amp, difference-amplifier and instrumentation amplifier for this purpose. What I first understand is, if I use a difference-amplifier or an instrumentation amplifier I have to use a split-supply(or maybe some reference voltage techniques which will reduce the range I don't know actually). Since the only option left for me is an op amp option, the article mentions the following issue for that case:
The drawbacks to low-side sensing are disturbances to the system load’s ground potential and the inability to detect load shorts. Figure 2 depicts a typical low-side sensing scenario.
And below Rp or Vp illustrates this:
My question is, in my application would that be an issue as well? I mean I can live with 100mA error. I couldn't find a topology where I can use a single difference amplifier with a single-supply. Is that possible? Or how can I minimise the error introduced by ground?
2-) I used LM358 as an active filter with unity gain and it follows another LM358 as an amplifier with a gain of two(to match 0 to 5V range to the ADC).
Green is the swept PWM voltage across Rsense; blue is the output of the active filter with LM358 and the red is the final output. Is LM358 proper for this application? And is 0.33 Ohm shunt resistor is high enough?
3-) Basically the question is do I need a gate driver for this MOSFET(for power dissipation concerns)? According to the data sheet this is a logic MOSFET. But still some in my previous question told me I still need a driver for since the MOSFET has capacitance which will drive excessive current.
But one of the commentators told me that I need a special driver such as this one. But the rest didn't find it as an issue. So I'm confused how to drive this MOSFET properly. Here is what LTspice shows the MOSFET's power at %95 PWM: