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Original question:

[FAQ] How do you generate isolated power for a digital isolator?

Transformer

Ueliton Rodrigues
Prodigy 65 points
Other Parts Discussed in Thread: SN6505B

Hi there,

by using a 1:1.1 transformer, I intend to use unregulated output. Is it recommended (without the LDO IC)? 

My application is rated at 5V as Vin and the Iout needed is around 500mA. The temperature grade of the application is 105C.

Regards,

Ueliton

  • 0
    TI__Genius 17100 points

    Hi Ueliton, and welcome to the E2E forums!

    Transformers with 1:1.1 turns ratio are recommended for unregulated 5V output since there is no LDO dropout voltage to accommodate. Transformer output voltage typically decreases as load current increases, so please ensure your transformer can supply the necessary voltage at 500mA loads and is rated for the highest operating temperature. Has a transformer for this system been selected? What is your acceptable power supply tolerance?


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Prodigy 65 points

    Thank you Manuel,

    The transformer selected is Wurth 750315371 recommended in the SN6505 datasheet: (rated at 1A)

    I plan to use this transformer in the following circuit, without LDO regulator.

    A plan B would be add a LDO regulator to output 3V3, in order to accommodate the dropout voltage, but the desirable is to keep the output at 5V.

    Regards,

    Ueliton

  • 0 in reply to Ueliton Rodrigues
    TI__Genius 17100 points
    Ueliton,

    You're welcome! This transformer is good for 5V:5V use up to 125C; note that it is only compatible with the SN6505B. The only considerations I ask you to keep are placing the 10uF capacitor on the primary side close to the transformer on the PCB and place an additional 0.1-1uF capacitor close to the SN6505 Vcc pin.

    Thank you for posting to E2E! Please feel free to follow up with results or additional questions by replying to this thread or using the yellow and red buttons on the top right corner of this window.


    Best,
    Manuel Chavez
  • 0 in reply to Manuel Chavez
    Prodigy 65 points
    thank you very much again.