This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV425: Open loop vs closed loop design considerations

Part Number: DRV425
Other Parts Discussed in Thread: DRV421, , DRV421EVM


From a customer of mine I received the question what the design trade offs are between an open loop vs a closed loop configuration. Devices in question are the DRV421 and the DRV425. Can you give a short summary or provide technical documentation on this topic?

Many thanks in advance.

  • JuMar,

    Thanks for using the forum to get your question answered.  I will quickly give a summary of the trade offs for each.  

    Closed Loop:

    • More Accurate
    • More immunity to outside magnetic fields due to magnetic core
    • Limited range due to compensation coil driver.  We have application note on DRV411 that can be used to increase output voltage and current range of compensation coil drive with external circuitry
    • Core must be designed
    • Higher bandwidth due to transformer effect on the magnetic core, limited by Diff Amp (2Mhz).
    • Measurement done by measuring current going through compensation coil.

    Open Loop:

    • Less Accurate
    • Limited immunity to outside fields. 
    • Uses Ampere’s Law to calculate current by measuring the magnetic field
    • Eliminate external magnetic field by using 2 DRV425s explained in Bus Bar Theory of Operations.
    • Bandwidth approximately 47Khz  or half of that if using analog circuit in 100A Bus Bar EVM

    First of all the closed loop system would normally be the more accurate but it is limited and a magnetic core would need to be designed to get it too work.  This requirements of the core are described in the datasheet and can be seen in the DRV421 System Parameter Calculator.  To help design with the DRV421 we have other application notes in the DRV421 Technical documentation folder.  We also have the DRV421EVM that can be purchased to evaluate with an external core.  

    The DRV425 can measure larger currents but will be based on the mechanical design on the bus bar.  All this can be seen in the Technical Documents and Software tools in the DRV425 Product folder.

    Of course there are many other designs considerations for both above is a quick description and some documentation and tools that would help in either design process.