Thanks, Aubrey. I was thinking of using it on an analogue variable power supply, before the main pass transistor. Apart from being able to switch the output off electronically, you could get a ground-referenced voltage proportional to output current - very useful for measuring output current using a standard DVM module - which on a variable PSU is otherwise not easy.. Looking at the specs for your IR3314, I think it would work ok. I'll look at the others as well. Are these things expensive?
This is an incredibly complex question. What is a good price for me is really expensive for someone designing for the mass market. Before I overwax philosophical though, it seems to me you are only interested in a single unit, so I will only state the price from Digikey for the automotive version AUIR3314S is C$4.81. (C$1 is approx US$1.) Apparently it is still available in a TO220 pack, if you want ease of connection although you may struggle to find it in that format although I see Digikey have 6 at C$6.95 at the moment and Mouser have it in abundance.
Speaking of high-side power switches with protection and diagnostic functions, have you read Infineon's ADVANCED SENSE Calibration and Benefits guide (http://tinyurl.com/ADVANCED-SENSE-1-0)?
As an aside... I happen to know that the guys who wrote this little rascal are incredibly clever and handsome and witty ... the words all appear to have been hand-picked at the crack of dawn while the morning dew is still glistening on them, and it goes without saying that the quality of the diagrams is fantastic...
the words all appear to have been hand-picked at the crack of dawn while the morning dew is still glistening on them,
These are the exact same words that I saw on an old recipe for making Rose Petal Jam. (new recipes like this, lose the magic!) I printed the manual out, shredded it and spread it on bread- but it doesn't taste anything like jam!
Seriously though- a well written document. Infineon obviously has good taste in authors.
@Aubrey, thank you for sharing information on these current sense devices. I was not aware of these devices and never used so far. But looks like I sould be able to make use of these devices in my designs. You mentioned about calibration. Do these devices require runtime calibration or one-time calibration in the factory before shipping? Without calibration does it make a huge deviation or could the tolerance be accommodated in the firmware if too much of accuracy not needed?
You mentioned about calibration. Do these devices require runtime calibration or one-time calibration in the factory before shipping?
We would generally calibrate as part of the test process during manufacture. I don't think they need run time calibration- if one needed that sort of accuracy I would imagine that one would use some different form of external current measurement. I would add that I have only worked with the IR device. The others may be different.
Without calibration does it make a huge deviation or could the tolerance be accommodated in the firmware if too much of accuracy not needed?
I am sure you can use software to handle the variations. The current mirror ratio can vary from 4800 to 6000 with a nominal value of 5300- a variation of about +/- 10%. There is a variation of +/-5% over the temperature range and an offset of about 150mA at a 2A output. You make the choice based on your application, I guess.
If you look at the earlier post (in this thread) from Max (about 5 posts ago) he refers to an Infineon application note that actually discusses calibration of this sort of device.
Do these devices require runtime calibration or one-time calibration in the factory before shipping?
The thought occurs to me that if you are reading the signal from the drivers you would be using and ADC and some additional circuitry, at the very least probably a resistor to convert the mirror current to a voltage. The ADC may also need some calibration, and it would be better is the whole thing was calibrated as a system. If you go to the second post before yours, you will find a pointer to part 1 of a blog I did on system calibration.
True, I agree with you on that it better be calibrated along with the ADC as a system. One could use the ADCsoften available built-in the modern microcontrollers. I will check out your & Max's blogs. Thanks for the information!
Hi Max, Thanks a lot for sharing the guide. This is a pretty elaborated description about the calibration methodology and the advantages of the newer devices with advanced current sensing technique, which make the calibration easier. I am also impressed to see the option for "no calibration", where the "typical" slope and offset correction factors could be used from the datasheet instead of adding a calibration process during production...this is good for the application where accuracy is not that important. Thanks!
Just so happens I was looking for current transducers the other day, under Sensors -> Current Sensors on Digikey (notably NOT under ICs -> Linear "anything") and I have to admit I was immediately impressed at the array of actual application specific ICs available. You can get prices down around 51 cents in quantities of a few thousand for some configurations, notable vendors in the low end include Allegro Microsystems and Silicon Laboratories. I'd emphasize this is for a range up to tens of amps, if you go higher into industrial motors and such you'd likely look at something like the LEM units which are a space- and cost- saving Hall effect replacement for a current transformer but in a higher price product class. But I'd admit until I "stumbled upon" the previous class of chips I wasn't really aware of them, thought perhaps you folks might not be either, might want to go there and crack open a data sheet or two.
notable vendors in the low end include Allegro Microsystems and Silicon Laboratories. I'd emphasize this is for a range up to tens of amps, if you go higher into industrial motors and such you'd likely look at something like the LEM units
I have used the Allegro hall effect parts as well as current transformers and both form a part of my arsenal. I haven't looked at LEM for a while now, I will follow your reccomendation.
This looks a very interesting device. I only seem to find a product brief. Do you know if there is a data sheet available? Perhaps it is still preliminary. I did find a YouTube video, but not much else. There is also supposed to be an evaluation kit, but I can't find stock of it or the part anywhere.
@Aubrey: Re:Do you know if there is a data sheet available? Perhaps it is still preliminary.
Yes, the datasheet is in Max's inbox - I asked him to forward it to you since I didn't have your email address readily available :-)
Correct, the part does not launch in production until Dec13/Jan14, so the datasheet is still a Target datasheet and the Final datasheet has not been released on the website yet. However, samples are available!
Unfortunate that the only units with status indication, the ZXMS6002G and ZXMS6003G have a feeble 500mohm Rds , what kind of automative load only uses 1A? , heck a simple PTC placed in close proximity to the MOSFET tab would provide sufficient protection for a 12v / 1A load.
Have you seen the DRV101 , in a TO220 5pin package , meant for solenoid driver, hits it hard at first then throttles back to PWM, interestingly it has a fault output for both under and overcurrent.
I've also looked at using the UC2845 (usually a current mode flyback PWM driver) driving any old mosfet. If you average the PWM signal (while it's running closed loop) as an analog voltage , you can determine whether it is open or short circuit. But it won't go to 100% duty so only good for bulbs and coils / motors.
Underdriving the gate is a big MOSFET killer , so some kind of de-saturation detector would be helpful.
I've also looked at using the UC2845 (usually a current mode flyback PWM driver) driving any old mosfet. If you average the PWM signal (while it's running closed loop) as an analog voltage , you can determine whether it is open or short circuit.
This is a great idea. You shoul;d submit it to EDN's Design Ideas- make yourself a few bucks.
Have you seen the DRV101
Thnaks for the pointer. I recently saw a TI part, but was only rated to 20V, for automotive applications. This one I can use!
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