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INA302-Q1: Understanding behaviour of two Current sense Amplifiers in parralel

REDDY Y
Intellectual 870 points
Part Number: INA302-Q1
Other Parts Discussed in Thread: INA381-Q1, , INA240-Q1, INA302, INA240, INA381

Dear TI Team,

i would like to replace our existing Over Current  Latch circuit (Charge & Discharge- designed with INA240-Q1 & Comparator + Discrete Components)  with INA302-Q1 or INA381-Q1.

Redesign we are planning to go for only to reduce the component count in design.

As current sense IC (INA240A2) is very accurate than any other ICs, i would like to reatin it and replace OC comparator + Latch section with INA302-Q1 or INA381-Q1

in this case i have to use two current sense ICs. i would like to understand if there is any problem with 2 CSA in parallel. 

we expect INA240A2 section to be erroneous free from the new CSA in parallel ( INA302-Q1 or INA381-Q1 )

Pls review and provide your feedback to proceed further with design activity. 

i have a hand sketch block diagram ready. will share via DM/Private message/Mail

  • 0
    TI__Expert 4720 points

    Hello,

    The main problem with putting two CSAs in parallel is the Ib (input bias current) of the current sense amplifiers. So for this reason it is important to create a same sense point and connect both CSAs to that sense point. There will be error if you would make the parallel connection of one CSA on the sense lines of the other. 

    The next problem is considering the voltage ranges of both CSAs. There are protection diodes in the CSA that will activate when abs max ratings are violated which can change the behavior of the CSA that may cause errors in the other CSA's output.

    If you would like you can PM me the hand sketch and I can look at it.

    Regards,

    Castrense

  • 0 in reply to Castrense Nigrelli
    Intellectual 870 points

    Dear Castrense,

    Thanks a lot for detailed explanation.
    1. Sense point we will take care of in the layout. and also fou our design : 10A-20A error (for 500A range) in Over current detection & latch is still acceptable. 

    2. Voltgae range of Both CSA's wont be a problem in our case in my opinion as CSA's are operating on low side shunt. correct if i am wrong

    I shared Hand skench diagram through PM. Pls review it and share your feedback

  • 0 in reply to REDDY Y
    TI__Expert 4720 points

    Hello,

    1, Before we go any further with the INA requirements, you have singled out INA381 and INA302 those have comparator and current monitoring capabilities. I understand that you are very keen on keeping the INA240. Maybe we should try and find an INA with just a comparator out? Or an INA that can replace the proposed two chip system with one chip (like the INA381 but more accurate)?

    2, If there is any switching and inductance a negative spike can happen that might exceed the negative abs max rating.

    To help out more I will need to know more about the system, and you may not want to share online. If you want we can start an email thread to explore this further.

    Regards,

    Castrense

  • +1 in reply to Castrense Nigrelli
    Intellectual 870 points

    Dear Castrense
    i have sent an email. pls check and provide your feedabck