• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 15 subscribers
  • Views 833 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

Original question:

SN6501 Isolation Transformers for 15V

SN6501: SN6501 Isolation Transformers for 10V

ibbidy2
Prodigy 60 points
Part Number: SN6501

I would like to generate a 10V isolated supply with the 6501, the input could be 5 or 3.3V.  The output current is 8mA max with transients in the 0.5mA range.

Is there a recommended transformer for this application?  I see the voltage doubling circuits in the datasheet but no recommendation for a transformer for this type of circuit (unless I missed it)

Thank you

  • 0
    TI__Genius 17100 points

    Hi Ibbidy,

    Thank you for posting on E2E and providing the current and voltage specs required on your system output. The SN6501 can comfortably supply 10V at both Vcc = 3.3V and 5V. This can be achieved by using transformers with an N > 2 turns ratio or a transformer with N = 1.1 - 1.3 turns ratio at 5V with a bridge rectifier, as shown on page 21 of the SN6501 datasheet.

    Factors to consider are:

    1. Are you driving a capacitive load >5uF?
    2. Is your output going to be LDO regulated?

    If the answer to question 1 is yes, please consider implementing a soft-start circuit or using the SN6505. A 5uf capacitor is sufficient to use as a normal output cap. Using an LDO will require at least an N = 1.3 turns ratio for margin.

    To achieve 10V on your system output using a 1.3 turns ratio transformer and bridge rectifier, TI recommends the WE 760390014 in our datasheet. Something to keep in mind is since voltage is double through the transformer and rectifier, the SN6501 will have to sink/source more current on the primary side. 8.5mA (or 8.5x2xN mA) max will not be a problem.

    Please typically anticipate responses during normal business hours M-F.


    I hope this is helpful! Please let me know if there are more details I can provide or if you would like to implement the 5V:10V differently.


    Have a great weekend,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Prodigy 60 points

    Manuel,

    Thank you for the prompt reply.

    To answer your questions, yes, the design will drive about 200uF (mainly IC decoupling caps)

    Yes, an LDO will be used.

    Good point about the current being higher on the primary side.  For my application I actually have a supply that is 48V but has about 4k ohms of impedance.  Thus the input voltage varies from 48V (no load) to 16V (8mA load).  I couldn't find a direct fit for this so I was hoping dropping the 48V to 5V with regulator and using that to drive the SN6501 might work.  (I'm open to other suggestions).

    Efficiency isn't critical for this application, but total input current cannot exceed 10mA.  Cost and simplicity is important, both of which the 6501/5 satisfy.

    Again, thank you for your help!

    ibbidy

  • 0 in reply to ibbidy2
    TI__Genius 17100 points

    Ibbidy,

    You're welcome! Given the 200uF caps connected to this isolated supply, the SN6505 will be the device of choice. Building on the simplicity factor, LDOs are an effective solution to ensure constant voltage is supplied to the transformer and SN6505 - may I recommend the 5-V LM2936? Or any of the LDOs from this search.

    Thanks for posting to the E2E forums; we're glad to help!


    Best,
    Manuel Chavez