• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 64 subscribers
  • Views 342 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LP5900 with No input but 3.3V forced at Output?

Dean Banerjee
Mastermind 28001 points
Other Parts Discussed in Thread: LP5900

Hi,

I have a question regarding the LP5900 linear regulator.

The idea is to give the user the option to regulate the supply down from 5V to the needed 3.3 V through the regulator, but not force this option on them.  So what I want to do is have a 5V ad 3.3V connector.  They can hook up the 5V conenctor and power through the LP5900, or connect the 3.3V supply and NOT connect the 5V and power directly from this. 

But this makes it so that there is no input on the LP5900, but the output is hooked to 3.3 V.   Will this cause a problem?  WIll the LP5900 load down teh circuit?   The Enable pin is tied to to the supply, so this would als be low.

 

Regards,

Dean

  • 0
    TI__Prodigy 160 points

    Hi Dean,

      Thanks for your questions.

      basically, from datasheet, page3, absolute maximum rating, we can see Vout can withstand 6.0V max voltage. I don't see any auto discharge and reverse protection circuit on the device, so maybe you are safe when "there is no input on the LP5900, but the output is hooked to 3.3 V "

      But I have to point out, you need to be very careful when you switch the "connector",  which will very likely  trigger voltage spike on Vin or Vout, the spike might be high than 7V and cause EOS damage.

  • 0
    TI__Prodigy 80 points

    Hello Dean,

            Nice to know you.

            Based on Jonathan's replying, I want to know more informaton.

            Could you help to confirm in this case,  when LP5900 Vout is  hooked to 3.3V,  what's the status of Vin?

            In LP5900, there has a diode between Vout and Vin,  the  anode of diode is connected to Vout, the cathode is connected to Vin.  When the Vout of LP5900 is hooked to 3.3V, if  Vin Pin is floating,  3.3V supply should not be loaded down ; if Vin is connected to GND,  i think 3.3V will be loaded down.

           Any concern or question, please don't hesitage to let us know.  Thanks.

            Best regards

            Bing