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LM4041D: LM4041

Barry Haworth
Prodigy 20 points
Part Number: LM4041D
Other Parts Discussed in Thread: TLVH431

This is a question relating to the adjustable version of the LM4041. The first thing that I would like to understand is what is the off-state anode current (ie when adj is connected to cathode) and how does this vary, including over temperature?  

I have an over-voltage vehicle load-dump protection circuit proposal (as shown) using the LM4041 and would value feedback regarding its functionality and any issues that may befall this design? 

Any and all feedback would be very much appreciated, thank you. 

  • 0
    TI__Genius 9790 points

    Hello Barry,

    Unfortunately we do not test for this spec on this device. You can consider using the TLVH431. It is a similar part and includes an off state current spec. 

    I also do not think this circuit will work correctly. The cathode of the shunt regulator needs to be connected to the gate of the mosfet. See this circuit for an example.

    Thanks,

    Walter

  • 0 in reply to Walter Zollinger
    Prodigy 20 points

    Good day Walter, I thank you for your kind response. Well, the circuit I provided using the LM40401 seems to work OK in all aspects except the MOSFET gate does not go to ground and is lifted to about 1.5V due to the LM4041, I thought this may be the operating current for the LM4041? Also, just curious as to why TI would suggest using the LM4041 in many of its application examples that would otherwise succumb to potential malfunction if the off-state anode current was not known? See attached TI example. I do however appreciate your example using the TLVH431 but the simplicity of the design using the LM4041 does hold a lot of advantages being that it also incorporates current limiting and hysteresis not to mention that it works with much higher voltages >150V? If you do have any further feedback than I would really appreciate that? Many thanks and kind regards

  • 0 in reply to Barry Haworth
    TI__Genius 9790 points

    Hello Barry,

    My mistake the gate is connected correctly. The 431 family and LM4041 have different input architecture.

    The circuit should be designed so that the minimum cathode current is always present. 

    The LM4041 only has a recommended max voltage of 10V or absolute max of 15V.

    Thanks,

    Walter

  • 0 in reply to Walter Zollinger
    Prodigy 20 points

    Hello Walter and thank you once again for your kind feedback. Yes, noted about the 10V limitation on the LM4041. BUT in the supplied circuit the LM4041 is protected by the 9V1 zener so it never goes over 10V even if the input supply is 150V? Just to wrap this one up please, are you please able to confirm that the 1.5V that I am seeing at the MOSFET gate is a result of the LM4041 operating current, which is about 30~40uA, flowing into the 47K gate pull-down resistor? Like I mentioned, the circuit works really well otherwise and I have tried it with the direct application of 70VDC and no problems. Would just be nice to know where that 1.5V on the gate is coming from and how stable it is? Many thanks and kind regards Barry

  • +1 in reply to Barry Haworth
    TI__Genius 9790 points

    Hi Barry,

    Yes the 1.5V offset is from the current through the LM4041. It should be stable and the zener diode is fine too.

    Thanks,

    Walter