You are seeing this behaviour in simulation or real circuit?
I haven't made real circuit yet. I think I will only see this behaviour in simulation, I read datasheet carefully and I didn't see any tips about that. I don't understand how LTC7000 detect that the current is raised above 10 Amps! because the only thing that LTC7000 see is the shunt resistor voltage. There isn't any feedback to LTC7000 to detect load current except shunt resistor voltage.
Thanks for your point about BAT54, We used this shunt in previous prototype:Hi,
What exact type of shunt did you use. Did you use Kelvin wiring technique?
Also, please show us your PCB layout.
Btw: BAT54 is specified for 30V only. You should use a higher voltage one.
Klaus
Excellent attention, I tune current load using R10 and duty cycle, in this picture load current is set about 9 Amps. We need to detect load current up to 200 Amps.MOSFET current will not go above your 50V in / 6 ohm load unless
you explicitly apply a short.
I guess you'd need to look at the DC-DC core to see if it, itself, is
meddling (like internal current sense for current mode control,
could house a "backstop" current limit?).
But you could just put a switch on the OCP FET drain and see what
happens with a simpler, more focused testbench of just the current
limit.
Hi,
The shown PCB layout does not fit to the shown schematic.
Don't confuse us with random informations.
Please show the according PCB layout.
Hi Klaus, The PCB layout that I have attached is for my previous version, I made that with a shunt resistor and current sensing circuit using Op-Amp. It wasn't as fast as possible and we should change our design and use LTC7000. Before making PCB I want to simulate it.Hi,
The shown PCB layout does not fit to the shown schematic.
Don't confuse us with random informations.
Please show the according PCB layout.
Klaus
LEM current sensors are extremely expensive for high current measurements. Also they are too big and we don't have enough space. We used shunt resistor and Kelvin connection in my designs and measured current up to 200 Amps without any problem. For more safety I need to add over current protection in my designs and now I have this issue with LTC7000 that it doesn't work when load current goes above 10 Amps.I think you would be better using a LEM current sensor for your 200 Amps.
Kelvin connection for a 200Amp will be challenging.
So too the effect of layout and stray inductance etc.
Possibly also use IGBT, as FET will sweat trying to break 200Amps.
Hi,
does this hold for a slow rising curren t, or only for fast slopes?
In your SPICE schematic I do not see an RC input filtering, so I would asume there might be an impedance mismatch causing a high voltage drop across your shunt due to the shunt impedance for fast transients. Consequently, this leads to a limiting of your current. Have a look here [1].
[1] https://www.planetanalog.com/current-shunt-resistor-inductance-it-matters/
Hi, Thanks for your excellent point. I replaced my half-bridge with a simple resistive load and the problem solved. As you mentioned high ringing across shunt resistor due to parasitic inductance and high di/dt I should your a RC filter in my feedback path. I attached the simple circuit that it works properly with resistive load.Hi,
does this hold for a slow rising curren t, or only for fast slopes?
In your SPICE schematic I do not see an RC input filtering, so I would asume there might be an impedance mismatch causing a high voltage drop across your shunt due to the shunt impedance for fast transients. Consequently, this leads to a limiting of your current. Have a look here [1].
[1] https://www.planetanalog.com/current-shunt-resistor-inductance-it-matters/
BR
Let´s say you have two children. One is sick, the other is healthy.The PCB layout that I have attached is for my previous version
Your Rsen is 50uR.....the noise will likely obliterate the measurement.
I dont even think its possible to properly kelvin connect that.
Hi Klaus,Hi,
Let´s say you have two children. One is sick, the other is healthy.
Which one do you show to the doctor?
I won´t annoy you by asking for the same a third time.
Klaus
The problem with Hall sensors are low response time. I need a very fast OCP circuit.Your Rsen is 50uR.....the noise will likely obliterate the measurement.
I dont even think its possible to properly kelvin connect that.
What about one of those Hall sensors from (i forget the name now), might by MPS, or ....i think its a Japanese company, forget the name.
Are you talking about a real circuit? Then it´s urgent to show us your wiring!I haven't made the new version with LTC7000 yet.
I am only talking about simulation. After that I will make real circuit with LTC7000. It's a very good IC and have all of protections that we need. In previous version I made OCP, OVP and UVP using multiple Op-Amps and compactors. It wasn't as fast as possible.Are you talking about a real circuit? Then it´s urgent to show us your wiring!
Indeed if you don´t use a proper PCB (layout) then your test makes no sense at all. Read and follow the "Applications information", especially the "PC Board Layout Considerations" If you don´t follow them, don´t be surprised if the Circuit does not work as expected.
Or are you talking about a simulation?
Klaus
The problem with Hall sensors are low response time. I need a very fast OCP circuit.
Thanks for great resourcesPrecision Measurements :
Thermoelectric, Kelvin, Noise :
PCB Considerations :
How To Use Trace Width Calculator(Fundamentals)
Calculation of appropriate trace width calculator sizes for current carrying is an important requirement of circuit board development.www.wellpcb.com
Regards, Dana.
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