• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 304 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.

LT1054: Using schottky instead of external transistor

Dai
Intellectual 270 points
Part Number: LT1054
When using make negative voltage, as written in datasheet P23 fig. 30, LT1054 needs external transistor to prevent Vout from being pulled above GND during startup. Is there any problem to use schottky diode between Vout and GND instead of the external diode? And can I know about substrate diode spec in LT1054?
  • 0
    TI__Guru* 78440 points

    Hi,

    Thank you for posting.  A Schottky does does not prevent the issue, because the pin can still be pulled to one diode drop above GND.  The transistor prevents it from becoming >0V.   So, the safe approach is to use a transistor as shown in Figure 30. It just requires a small signal transistor.   By the way, the substrate diode spec is not available, as we do not characterize parasitic devices.  

    Thanks,

    Youhao Xi, Applications Engineering.

  • 0 in reply to Youhao Xi
    Intellectual 270 points
    Hello, Thank you for your reply. > The transistor prevents it from becoming >0V. Yes, but I guessed if I choose less small Vf schottky than substrate diode Vf, it will operate. >By the way, the substrate diode spec is not available, as we do not characterize parasitic devices. OK. Thank you.
  • 0 in reply to Dai
    TI__Guru* 78440 points

    Hi Dai,

    Thank you for understanding. What you really need to know is the worst case min Vf of the substrate diode, which is why we cannot specify to allow you to have a safe selection of the external diode.

    Best Regards,

    Youhao