by roodesign on Sat Mar 16, 2013 10:11 am

Hello there, new to Arduino, and am going to use one to control various systems in a car that I am building...please see just the basic stuff...nothing fancy...self canceling directional lights, pwm headlights, Fans and other lights, solenoid valves for a heated Vegetable oil system, and etc.

my question is can I switch this IR3313(S)pbf high side switch with a Arduino pin, or do I need a transistor go between?
datasheet is here:
aplication note here:

it's confusing to me (newby) to understand what the input requirements are.
on the last page of the application note it says, to run it without current feedback (fine with me) you can run it with one wire.
it further says that "when VCC-VIN reaches VIH" it switches on...HUH?
VCC is the supply being switched
VIN is the input signal
VIH is a threshold that says 5.4-6.2v

Please help !
I am just learning this micro-controller stuff, if anyone has bright ideas or better ways to do what I am trying to do please let me know! any contributions will be recognized on my blog

-roo trimble
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Joined: Sat Mar 16, 2013 9:46 am

by Zener on Sat Mar 16, 2013 3:42 pm

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.

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by roodesign on Sun Mar 17, 2013 6:34 pm

wow, I think that I am starting to understand after reading your post for the 7th time! Thanks so much for the long and short answers! for using these particular switches, I looked at options for high side mosfets for automotive use and these came up...tell me if there is a better way...I am still going to have fuses in each circuit. extra protection sounded good...these mosfets are heavier duty than I need for most circuits. The only big circuits that I want to control are the fans on the heater and radiator and the headlights. The other circuits are either regular automotive relays or led lights.

anyway if there are better switches for the smaller loads...please let me know.

at the moment, I am thinking that I have about 16 outputs and about the same inputs, I have a Teensy 2.0 ++ on the way.
I will post a diagram in the next day or two for comments (please)

thanks again for all the info!

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Joined: Sat Mar 16, 2013 9:46 am

by Zener on Sun Mar 17, 2013 8:23 pm

The easiest way to drive a load is with low side switching, using a N-channel fet. Then you don't need any other parts. And those are less expensive also. But if you want to high side switch then just use a P-channel fet. Then you will need the a small N-ch or NPN to turn it on as shown in the datasheet we were discussing. A P-channel fet is just the fet without all the overcurrent protection stuff that is in the 3313. You should be able to select one using the parametric search on DigiKey. Keep in mind often times they specify a max load current based on a pulse and the continuous current is much lower. It never hurts to go a little bigger and get a little smaller Rdson. And you have to decide of it will be surface mount or through hole of course.
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