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TINA/Spice/LM4040: Precision shunt regulator failure behavior

Albert Huang10
Prodigy 10 points
Part Number: LM4040
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

In designing my project, I was basing my design on a prior project that used a 3.3 V input voltage Vs and an appropriately sized shunt resistor Rs. Unfortunately, I hooked Vs to a 5 V input and exceeded the maximum specified current for the device for some minutes (which is 15 mA, according to the datasheet). However, I only exceeded it by 1 mA, so I haven't let out any magic smoke.

What is the expected behavior of a precision shunt like this if it's failed? Currently, I am obtaining 4.3 V across my output and ground, indicating to me that the LM4040 is doing something, though I'm not getting the desired 2.5 V.

  • 0
    TI__Expert 3835 points

    Hi Albert,

    Once a device is outside of its maximum specified current, it is in an unknown state and we cannot guarantee any mode of operation. If you are powering up the device and obtaining 4.3V, then the LM4040 is failing to regulate to its desired 2.5 volts.

    The device does not necessary need to produce any smoke to show that it is failing. As you can see, the wrong output voltage indicates that the device is damaged due to exceeding its maximum specifications.

    Hope this helps,

    Ethan