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Using adjustable LM4041 shunt voltage reference instead of LM431

Part Number: LM4041-N
Other Parts Discussed in Thread: LM431, LMV431, TLV6713, TLV1701

**** Using adjustable LM4041 shunt voltage reference instead of LM431 in the ciruit described in app. note AN-1533:

Over Voltage Protection Circuit for Automotive Load Dump.

How to properly connect adjustable LM4041 since FB of LM4041 is referenced to the anode, but FB of LM431 is referenced to the kathode?

Please see attached PDF file.

Thank you,Using adjustable LM4041 shunt voltage reference instead of LM431.pdf

Regards,

  • The LM431 compares the voltage from FB to anode to check for 2.5V. This is due to the architecture of the LM431. The following app note discusses the behavior in more detail.

    The LM4041 compares the FB to the Cathode and checks for 1.233V. The behavior of the LM4041 is opposite and different from the LM431 and other 431 like families.

    The LM4041 cannot be configured like the LM431 in the app note AN-1533.

    If you need a lower voltage device instead of LM431 try the LMV431. This is a 1.25V device that is part of the "431" family that has the same behavior so it can support AN-1533.

  • Hi,

    Thank you very much for a quick reply.

    LM4041 is an attractive shunt voltage reference, because it has a low minimum operating current  65 uA.

    In the case, when the input voltage is a battery, it is important to have over-voltage protection circuit which consumes less power, (in the microamperes range).

    The over-voltage protection circuit with low current consumption can be designed with a standard zener diode, and transistors: NFET, NPN, PFET, PNP .

    But, such a circuit is not as precise as a circuit based on  LM4041.

    There are overvoltage controllers but they have auto-retry and latch-off features, which is not what I wont.

    I think, over-voltage ciruit based on LM4041 can be implemented as per the picture below, but  for systems up to 10V, because LM4041 has limited maximum voltage 10V.

    Note: the circuit is not simulated. This is just a concept.

    For higher Vin voltages, this circuit needs to be modified / improved in order to protect LM4041

    V2 over-voltage hreshold is set by R1 and R2 divider.

    Resistor R3 is placed from LM4041 anode and  GND.

    Hysteresis can be also added.

    In the normal operation mode, (when Vin is below treshold), Q1 is OFF, Q2 is OFF and Q3 is ON.

    When Vin is higher than the V2 threshold, voltage V3 across R3 would turn Q1 ON, which turns Q2 ON, and consequently, Q3 turns OFF, which disconnects the load.

    Current consumption in the normal operation mode (when Vin is below threshold) could be quite low by chosing higher values of R1 and R2.

    There is LM4041 current, and also some leakage currents from transistors.

    I appriciate looking into this issue.

    Thanks and regards,

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  • You are correct. I was under the impression you wanted to just directly replace the LM431. You have the correct way this device for comparator mode but it will have the 10V limit.

    If you are trying to lower Iq, I would recommend a low Iq reference + op amp for a comparator or a voltage supervisor ti.com/svs

  • Yes, using a combination of high voltage micropower opamp, comparator, voltage reference would be solution design over-voltage protection ciruit.

    For example, the TLV6713 Comparator is 36V and it has internal 400mV reference. TLV1701 is also 36V, micropower, but it requires an external reference.

    I checked overvoltage controllers, but they are expensive, and they have some additional features (internal delay, auto-retry, latch-off) which are meant for a specific function.

    I gave some thoughts about if LM4041 shunt regulator could work at higher voltages.

    Solution #1: Adding 8.2V or 9.1V Zener diode parallel to the LM4041 would protect LM4041, but the Zener would affect voltage rise time on R3, when the input voltage is slowly changing around the threshold.

    In that case, voltage on R3  is not going to be step voltage required to quickly turn on the transistor.

    Solution #2: Adding Zener diode in cascade configuration Vin - Zener - LM4041 - R3 - GND. I think this should work, but threshold tolerance is affected by Zener.

    Zener diode tolerance can be 1%, and Zener temperature coefficient is significant.

    Regards,

    Spring2020

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