5V regulator generating 5.92V

Discussion in 'General Electronics Chat' started by sujith.g, Nov 28, 2015.

  1. sujith.g

    Thread Starter Member

    Jul 7, 2015
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    HI,

    I have used the following 12V to 5V regulator. The part number is A6986F5V (STMicroelectronics). Problem is in 5 boards I designed and assembled I am getting different voltage outputs from the regulator ranging from 5.1V to 5.92V. But in my application, the maximum voltage I can accept is 5.2V. Please let me know what could be the reason for the extra voltage generated. Could it be soldering issue or any other problem with design. 5V_Regulator.png
     
  2. Bordodynov

    Active Member

    May 20, 2015
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    You measure produced no load? Connect the output 5V resistor. Example 470 ohms.
     
  3. sujith.g

    Thread Starter Member

    Jul 7, 2015
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    HI,
    But in some boards I am getting exact 5V with same setup. In my board this 5V is fed to 2 controllers. So they will be the load.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Are you sure your IC is not a fake, or reject?
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    What resistors have you got on pin 9 to set the output?

    Get yourself a proper regulator like a Lm2596...
     
    Last edited: Nov 28, 2015
  6. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    I was going to mention that but figure the OP had some special need for that chip. It seems like a way overly complicated chip. Those ones from TI are so easy to use.
     
  7. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Why don't you add a load an measure it? What is the harm? It should be tested that way ayway.
     
    sujith.g likes this.
  8. dl324

    Distinguished Member

    Mar 30, 2015
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    My thoughts exactly... Don't see how you could get more than 0.85V because you're feeding back the output voltage.
     
  9. Roderick Young

    Member

    Feb 22, 2015
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    Are you measuring the output with a digital voltmeter, or something else? It could be that the output is just very noisy, and you are picking up the peak voltage of the noise. I would use a ceramic capacitor, not aluminum electrolytic, for C18, as it appears that your switching frequency is 500 kHz. If you cannot change C18, at least put some kind of ceramic capacitor with as short leads as possible between the FB pin and the SGND pin. 0.1 uF is better than nothing, but if you can do 10 or 22 uF, so much the better. Also, if L5 is a purchased part, is it suitable for this application?
     
    Last edited: Nov 28, 2015
  10. Roderick Young

    Member

    Feb 22, 2015
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    He's using the part with the 5V suffix, so I assume the voltage is automatically set internally?
     
  11. Dodgydave

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    Jun 22, 2012
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    Well its not working
     
  12. Bordodynov

    Active Member

    May 20, 2015
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    I have seen the book, which the author described a similar case. He used a foreign regulator in its tester. In the study, he found work at the output of the stabilizer generation. He addressed to the author of the stabilizer and learned that a stabilizer designed for the current of at least 200mA. So I suggested to connect a resistor. In one my tester LM317 stabilizer is made at low output voltages 1.3V instead gave voltage 1.5V. When you hook up the load voltage becomes 1.3V.
     
  13. Roderick Young

    Member

    Feb 22, 2015
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    That much is certain.
     
  14. sujith.g

    Thread Starter Member

    Jul 7, 2015
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    HI all,
    Thanks for your reply. My end application is going to be automotive which requires several protection such as load dump, over voltage protection, load and line regulation, soft start etc. And the most important thing is my Regulator must be AEC qualified which is the reason I chose the following part A6986F5V. I feel it is only the IC problem as I faced that issue of output voltage going to 5.96V in only one of my boards. The rest of the boards are giving proper 5.0V,.5.1V.
     
    Last edited: Nov 30, 2015
  15. sujith.g

    Thread Starter Member

    Jul 7, 2015
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    HI Roderick,

    Yes currently C18 is a tantalum cap. I will try changing it to ceramic 10uF and check if it helps. And the inductor I have chosen is AEC qualified. So I hope that doesn't create a problem.
     
  16. sujith.g

    Thread Starter Member

    Jul 7, 2015
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    Yes I will try putting a 470ohm resistor and check. Thanks.
     
  17. sujith.g

    Thread Starter Member

    Jul 7, 2015
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    0
    HI,
    Pin9 is actually the feedback pin. THis is a fixed voltage regulator so I am not setting any resistors as per the reference design in daasheet.
     
  18. sujith.g

    Thread Starter Member

    Jul 7, 2015
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    Please find the datasheet attached.
     
  19. sujith.g

    Thread Starter Member

    Jul 7, 2015
    48
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    Hi all,

    Great news.!!!! Solved the problem. Was just a soldering issue. My bad.:rolleyes::rolleyes: I guess the thermal pad of the regulator (SGND) was not properly soldered to the pad. I resoldered it with an IrDA machine and it fixed the problem. I am getting a clean output voltage of 5.02V. Seems like the issue was the floating GND was acting as a fault trigger to shoot up the voltage to 5.89V. thank you all for your suggestions. :D:D:D
     
  20. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Good that you solved the problem.
     
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