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LMZ13610DEMO what happens if FB is disconnected

Other Parts Discussed in Thread: LMZ13610DEMO, LMZ13610

I plan to use the LMZ13610DEMO board to create a constant current supply by tinkering with the feedback from an external current sense resistor.  When the load is removed, the LMZ13610 will have no feedback to control the output voltage.  Will this damage anything?  My normal load will be 2VDC to 6VDC, so input voltage can be 12VDC.

Ron

  •  

    When the load is removed there will be no current in the sense R and the FB voltage will fall to zero.  This will cause the regulator to become open loop and force nearly the input voltage to the output.  This may not damage the regulator but may damage anything else connected to the output; such as the output caps.  Also, when the load is reconnected the regulator will require some time to recover, producing a large surge of current and/or voltage.  This is the usual behavior for a current source; you can not open the load without causing trouble.

  • Frank De Stasi said:

     

    When the load is removed there will be no current in the sense R and the FB voltage will fall to zero.  This will cause the regulator to become open loop and force nearly the input voltage to the output.  This may not damage the regulator but may damage anything else connected to the output; such as the output caps.  Also, when the load is reconnected the regulator will require some time to recover, producing a large surge of current and/or voltage.  This is the usual behavior for a current source; you can not open the load without causing trouble.

    Thanks Frank; what you describe is normal for a current source.  My concern was serval of the LMZ regulator.  If i choose output caps with proper voltage rating, it sounds like I shd have no problem.  To assure the LMZ doesn't fail from too high an output voltage, what's max input supply?  I didn't find this in the data sheet (or missed it)

    Surge currents to the load will not be a problem; I'm applying this to a special function battery charger.  

    Ron

  • Frank De Stasi said:

     

    When the load is removed there will be no current in the sense R and the FB voltage will fall to zero.  This will cause the regulator to become open loop and force nearly the input voltage to the output.  This may not damage the regulator but may damage anything else connected to the output; such as the output caps.  Also, when the load is reconnected the regulator will require some time to recover, producing a large surge of current and/or voltage.  This is the usual behavior for a current source; you can not open the load without causing trouble.

    Thanks Frank; what you describe is normal for a current source.  My concern was servival of the LMZ regulator.  If i choose output caps with proper voltage rating, it sounds like I shd have no problem.  To assure the LMZ doesn't fail from too high an output voltage, what's max input supply?  I didn't find this in the data sheet (or missed it)

    Surge currents to the load will not be a problem; I'm applying this to a special function battery charger.  

    Ron

  •  

    The max vin is 36V; abs max to 40V.

    Here are some things to watch for:

    1)  The output caps must be rated for your max input voltage.

    2) You may need to adjust the output caps to get a stable regulator.

    3) You may need a capacitor across the load to get good response or a stable design.

    4) Please be sure to test this carefully, since it is not a standard application.

    5) Please follow the layout guidelines in the data sheet.

  • My battery voltage is low, so input can be low, ca. 15VDC to 24 VDC, keeping me well within limits of the LMZ. Thanks for helping me confirm this should work.
    Ron