Re: IR3313(S)pbf high side mosfet switch & Arduino & Car
OK.... So, first of all that is a really cool looking vehicle you have there!
Now, for your question... would you like the short answer or the long answer? I will try to give you both.
Short answer: You need a transistor, as shown on page 1 of the data sheet where they show the "Typical Connection". They have a N-ch fet hooked up as open drain but you could use a NPN as open collector also, you would just need a base resistor in that case. Done.
Long answer: (Read and fall asleep at your own risk) I understand your confusion. That part is a bit hard to get your head around. First of all, just for the record, there are simpler ways to do what you are doing. However, this part here has built in overcurrent shut down, which is a neat feature if you want that.
There are a couple of reasons this part and data sheet are a little confusing. First of all, in the first paragraph they say "Over current shutdown occurs when Vst-Vin > 4.5V." However, Vst is never mentioned again anywhere on the data sheet. What happened? Well, what happened is when it is next mentioned at the top of page 3, it has magically turned into "Vifb", and Vst-Vin has magically turned into "Vifb-Vin@Isd". (I have a theory about why data sheets are so messed up like this but that is for another forum.) Now, even though they have said it 2 ways, I think they should have said "Over current shutdown occurs when Vrifb-Vin > 4.7V (typ)."
So now you say, Ohhhhhh..., still don't make too much sense. Here is the trouble. Most of the time circuits are referenced to ground. But in the case of P channel fets (and PNP transistors) everything is referenced to the Vcc. But...... we have an IC here in here also, and there must be a ground reference, AND you do have a logic ground, which is even shown on the schematic on page 1. Here is the deal: first of all the IC does have a "low rail", it is your input voltage Vin. That is why they keep referencing that. Notice that your actual ground is never connected directly to the chip.
So here is what you do: For every amp you supply to the load you will get 1/8800 of an amp through Rifb. Assuming your input got pulled close to ground, we will call Vin 0 for the sake of argument. Lets say you want shutdown to occur at 20A. 20/8800 = 2.27mA. Using Ohm's Law, R= V/I, = 4.7/.00227 = 2070 ohms. This is within the allowable range for Rifb.