Compact overvoltage, undervoltage, reverse protection with LTC4365

There are many circuit simulators available which are based on the original SPICE (Simulation Program with Integrated Circuit Emphasis) code developed at Berkley university at the end of ’60. Linear Technology developed their own version called LTSPICE IV very useful when you need to simulate circuits which use components made by LT. LTSPICE IV can be downloaded free of charge from http://ltspice.linear.com/software/LTspiceIV.exe. Let’s see how is possible to design a very fast overvoltage, undervoltage and reverse protection using few components (the pictures have been extracted from the official datasheet available at http://cds.linear.com/docs/Datasheet/4365f.pdf and from LTSPICE IV available at http://www.linear.com/designtools/software/#LTspice):

This schematic is the one proposed by Linear Technolgy in LTC4365 datasheet and it is available inside LTSPICE IV by selecting “Edit”, “Component”, “LTC4365” and “Open this macromodel’s test fixture”.  The components are set to have a OV protection threshold of 18V and an UV threshold of 3.5V:

The diagram shows relationship between Vin (blue) and Vout (green) on the y axis on a milliseconds scale (x axis full scale at 200ms). They are selected by adding a voltage probe at the input and at the output of the circuit once the simulation is run. As visible the protection response is very fast (about 10ms to drop the output to zero volt). The double mosfet has the function to protect the circuit in case of reverse voltage:

The LTC4365 has a recovery delay timer which introduce a delay of 36ms that filters noise at VIN and helps prevent chatter at VOUT: after either an OV or UV fault has occurred, the input supply must return to the desired operating voltage window for at least 36ms. The recovery timer is also active while the LTC4365 is powering up: the 36ms timer starts once VIN rises above UV threshold and VIN lies within the user selectable UV/OV power good window.

A voltage divider made by three resistors applied to two comparators set the UV and OV threshold as follow:

The data sheet gives details to calculate R1, R2 and R3 in order to set the UV and OV threshold as necessary.

A possible release of such protection could be the one we made for testing purposes:

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6 Responses to Compact overvoltage, undervoltage, reverse protection with LTC4365

  1. stephan schulz says:

    apparently this simulator can be used to get the right values:

    http://www.linear.com/product/LTC4365#simulate

  2. stephan schulz says:

    i am trying to get this chip working too for UV = 10 V and OV = 25 V
    but it’s not working and i am wondering if i calculated the resistors wrong.
    R1 = 121K
    R2 = 178K
    R3 = 57.6M
    otherwise i think i set up my circuit correctly.
    do you have any advice?

    • stephan schulz says:

      correction: i am using r3 = 5.76m

    • admin says:

      Hi Stephan,

      the values you found seem to be ok: if you try to simulate using LTSPICE IV you have the required OV and UV. Try to check the resistors (R1, R2, R3 are as reported in figure 1 of the official datasheet):

      R1=120K; (R4 in the schematic reported by LT SPICE IV)
      R2=180K; (R3 in the schematic reported by LT SPICE IV)
      R3=5.7M. (R2 in the schematic reported by LT SPICE IV)

      Please let us know if you have solved.

  3. Malcolm Fendick says:

    How can I get hold of the breakout board you illustrate?

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