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INA138: Ina138

Bruce Doan
Prodigy 190 points
Part Number: INA138
Other Parts Discussed in Thread: INA296B, INA169, INA168, AMC1301

Tool/software:

I am looking at a design example for a high side current sense for systems with very high common mode voltage. 

https://www.ti.com/lit/an/sboa295/sboa295.pdf?ts=1726922754966

What changed needs to be made to have this work at even higher voltages (650V)?

  • 0
    TI__Mastermind 31745 points

    Hello Appreciated Engineer,

    I am looking at you question and will respond shortly.

    Best,

    Peter

  • 0 in reply to Peter Iliya
    TI__Mastermind 31745 points

    Hello again,

    We truly apologize for the weekend delay. 

    In order to scale the referenced design to higher voltages you need to:

    1. Increase R3 to reduce unnecessary power loss.

    2. Replace Z1 with a Zener that has a larger breakdown voltage < current sense amplifier's maximum supply/common-mode voltage. So for INA138 Z1's reverse breakdown needs to be < 36V. Using a larger Zener voltage reduces the voltage drop/power lost through R3

    3. If 1 and 2 aren't possible, then maybe use a slightly more complicated floating supply voltage circuit that does not require as much regulation current/power loss.

    4. Replace Q1 with transistor (or stack of transistors) that can drop the 650V with some margin from drain to source.

    I would recommend either using a the largest rated amplifier (INA169 or INA168) to reduce power lost from the Zener regulator. If you need more accuracy you could use a voltage-output current sense amplifier (e.g., INA296B), but convert it into a current-output architecture using a Howland Current Pump as shown in the following documents:

    https://www.ti.com/lit/an/sboa358/sboa358.pdf 

    https://www.ti.com.cn/cn/lit/an/sboa513/sboa513.pdf 

    The other option is use a an isolated amplifier such as AMC1301.

    Sincerely,

    Peter