• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 1152 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.

TPS7A47: LDO not working as intended.

user5353358
Prodigy 10 points
Part Number: TPS7A47

I was designing an LNA and needed 4V at output of the LDO.I used tps7a4701 for the regulator and used any-out option for setting up the output voltage.But I get a variable output when I power up the  circuit. At Vin=3V I get Vout=3V and when i increase Vin Vout increases. Vout caps around  5.42V. You can check the design below.

  • 0
    Guru 140200 points
    Hi,

    could be a soldering issue. There's a bit too much soldering tin on the solder pads and many lints can be seen. Are you sure that there's no short circuit? What says the ohmmeter?

    Kai
  • 0 in reply to kai klaas69
    TI__Guru 55940 points

    Hi ,

    It is somewhat difficult to tell from your picture which of the ANYOUT pins you have tied to GND; however, it looks to me that you tied 3P2V to GND as well as 0P8V.  Unfortunately this will yield a nominal output of 5.4 V when the LDO has a high enough Vin to regulate.  

    In order to achieve the intended 4 V output, tie pin 8, pin 9, and pin 11 to GND.  4 V = 1.4 V (Vref) + 1.6 V + 0.8 V + 0.2 V.

    When Vin is lower than 4 V + Vdo, the LDO will operate in dropout mode.  While in dropout, the LDO does not have enough headroom (Vin - Vout) to regulate the output voltage and the output will follow the input voltage minus a small resistive drop in voltage.

    Please note that we also highly recommend having a same layer GND path for all bypass capacitors to the LDO GND pin in order to cut down on inductance.  This is particularly critical for Cout.

    Very Respectfully,

    Ryan