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LP2954A: LP2954A ground pin disconnect while power applied to input but not output

Jon Lavallee
Prodigy 50 points
Part Number: LP2954A

can i get some clarification on the statement in the datesheet that states the following

"The regulator output can be left connected to an active voltage source (such as a battery) with the regulator input
power turned off, as long as the regulator ground pin is connected to ground. If the ground pin is left floating,
damage to the regulator can occur if the output is pulled up by an external voltage source."

what exactly is the scenario for damaging the IC?  in this scenario the only connection being made is having a voltage on VOUT.  how could current flow anywhere that would cause damage?  i could see the potential for damage if there is a voltage present on VOUT and then the GND connection is made afterwords.  please clarify.  thanks. 

  • 0
    Prodigy 50 points

    my title is in error.  it should be 'while power applied to output but not input'

  • 0 in reply to Jon Lavallee
    TI__Genius 12910 points

    Hello Jon,

                    For the device, the output pin voltage will always be in reference to the Ground pin voltage. If the ground pin is left floating, there could be an Absolute Max rating voltage spec violation at the output pin that would damage the device. Excess voltage is sufficient to break down the transistors in the regulator and damage it permanently. Thanks!

    Regards,

    Srikanth  

  • 0 in reply to Srikanth Lolla Venkata
    Prodigy 50 points

    Hi Srikanth.  I have a similar question.  I want to make use of the internal 5V tap resistor divider.  I want to be sure that I can apply 20V at the output when there is no VIN and no damage to the part will occur.  Thanks.  

  • 0 in reply to Jon Lavallee
    TI__Genius 12910 points

    Hi Jon,

               This is a fairly old device and, unfortunately, we do not have information beyond what is provided in the datasheet. As per the datasheet description, you may connect a battery (20V in your case) at the output pin with the input power turned off and GND pin connected to ground. As stated in section 7.4.1 of the datasheet, please use a pull-up resistor (20KΩ ≤ RPULLUP ≤ 100KΩ) between SHUTDOWN and IN pins. The Abs max ratings for the OUT pin have not been provided, but since the device is rated to work for voltages up to 29V, the risk of damage would be very small for how you wish to use it.

               Let us know if you are interested in more modern devices that offer reverse-current protection. Thanks!

    Regards,

    Srikanth