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LM5017 UVLO

David Dean
Expert 2315 points
Other Parts Discussed in Thread: LM5017, LM5006, LM5008A

Hello,

  I am looking at the LM5017 and the high Vin(max) is ideal but I am concerned about the relatively high 9V Vin(min).  I did notice in the datasheet that the internal UVLO threshold for Vcc is only 4.5V.  What would happen if I use the UVLO pin to set a threshold of only 6V?  Would the part attempt to operate once Vin is high enough (but still below 9V)?  My Vout is set to 5V and I am not guaranteed a Vin as high as 9V in my system.

Thanks,

Dave

  • 0
    TI__Genius 11490 points

    Hi Dave,

     

    What is your minimum VIN? What is your max load. Maximum VIN? Do you need a UVLO function?

  • 0 in reply to Vijay86929
    Expert 2315 points

    Hi Vijay,

      My minimum VIN is unknown - the input power is provided by a generator that can be turning at an unknown speed.  The idea is that when the input voltage is sufficiently high, the regulator will begin generating 5V.  The lower Vin (min) the better, as it will allow for the 5V output at a slower generator speed. 

      So with all else equal, a Vin(min) of 9V will require a faster generator than a Vin(min) of 6V.

      I do not NEED a UVLO function - for example, if a 4.9V input generates, say, a 4.5V output, that is OK - I do not need the output to be either 5V or 0V.  It is important that the regulator not get stuck in a bad state at startup, of course....but it is ok if the output ramps up along with the input voltage.

    Thanks,

    Dave

  • 0 in reply to David Dean
    TI__Genius 11490 points

    Thank you for the clarification. What is your maximum load? Max VIN.

    LM5017 will start to switch as soon as VCC UVLO is cleared which will be ~8VIN. If you need to operate at VIN lower than that I suggest you switch to LM5008A(6V-100V) or LM5006(6V-80V). Depends on your load and max VIN.

    Thanks and regards,

    Vijay

  • 0 in reply to Vijay86929
    Expert 2315 points

    My maximum load is 500mA, so I can't use LM5008A (350mA).

    Max VIN is somewhat unbounded - a faster generator will give me a higher voltage.  I can protect against overvoltage but a higher Vin(max) makes that less critical.

    I am currently using the LM5006 but could benefit from the extra Vin headroom. 

    Thanks,

    Dave