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delteVSNS

Category: Hardware
Product Number: LTC7000
Software Version: -

Hello

I use the LTC7000 and try to measure the current.
My shunt resistance is 0.5 mOhm and I get very inaccurate or different values for the current measurement on IMON.

Also the overcurrent cut-off does not work.

Is my shunt too small?

Parents
  • Hello,  
    Today i change zhe Shunt resistance to 1 mOhm. Now it work mutch better. I got Values between 700 und 750 mV at IMON for 30 Amps.  The Overcurrent Shutdown works at 60 AMPs with 150 KOhm at ISET.

    however - in my case i Need a overvoltage Shutdown at 100 Amps an a Shunt-resistor of 0.5 mOhm. 

    maybe the LTC7000 is not the right chip for my application?

Reply
  • Hello,  
    Today i change zhe Shunt resistance to 1 mOhm. Now it work mutch better. I got Values between 700 und 750 mV at IMON for 30 Amps.  The Overcurrent Shutdown works at 60 AMPs with 150 KOhm at ISET.

    however - in my case i Need a overvoltage Shutdown at 100 Amps an a Shunt-resistor of 0.5 mOhm. 

    maybe the LTC7000 is not the right chip for my application?

Children
  • I don't know enough about the application to tell if you have the right chip but I can offer a couple of comments. IMON only works when the switch is on (TGUP-TS is high). IMON and the current limit are independent of each other. Let's assume you have a 0.5mohm resistor, ISET=100k, the switch is on (TGUP-TS ~= 12V), VCC = 10V, 100ohm + 1nF filter on sense, TIMER pin is open or has a capacitor to ground. I would try slowly increasing the DC load current from 0 to 60A while measuring the voltage between the SNS+ and SNS- pin with a DMM. At 60A, verify there is 30mV between SNS+ and SNS- pins and IMON is 0.52 to 0.68V (and TGUP-TS ~= 12V). Next, slowly increase the DC current and note the voltage measured from SNS+ to SNS- when the switch turns off. From there, you can try more dynamic loads (keeping in mind the TIMER delay if the current is moving quickly). Note that input capacitance is recommended and a protection diode/capacitance is required from GND to TS if the load has series wiring, etc. inductance (see Demo Board DC2537A schematic). Good Luck.

  • Hallp,


    The problem was that the 500uOhm shunt was distributed on two sides. (8 resistors in total)

    The measured values were too inaccurate.
    There were  vias and solder joints btween the Shunt Resistors.

    I have now use a singel special shunt with 4 connections.

    The whole thing now works perfectly and shut down exaxtly at 100 Amps.