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Original question:

Isolated bidirectional device for 10MHz, Vcc 1.8V-5V

ISO7731: Isolating a bidirectional SWD Connection

Dustin Walker
Prodigy 20 points
Part Number: ISO7731

Isolating a bidirectional SWD Connection

I use the JLink Ultra to connect to some uController.

The connection uses the SWD (Serial Wire Debug) Standard
With SWclk  (unidirectional)
and SWDIO (bidirectional)

I would like to run this circuit with the max Frequency of the JlinkUltra, which is 50MHz

You have a circuit for a high frequency I2C Connection (www.ti.com/.../slyt403a.pdf
Is it possible to adapt this circuit for the SWD Protocol?

The circuit should have 3.3V or 5V on the uController Side.

Thank you for your Help!

Dustin

  • 0
    TI__Genius 17100 points

    Hi Dustin,

    Thank you for posting, and welcome to E2E!

    It is possible to adapt the bidirectional I2C circuit in Designing a reinforced isolated I2C-Bus® interface by using digital isolators (SLYT403A) to other bidirectional communication standards. Functionality of the circuit is dependent on the external components used and their resulting compatibility with HI/LOW I/O voltage thresholds of the communicating devices.

    If you can share the HI/LOW voltage level thresholds for the JLink Ultra and MCU (or datasheets), we can provide targetted insight on the requirement mentioned above.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Prodigy 20 points

    Hello,

    I have more information now:

    Optimally this circuit shall work with two different microcontrollers: 

     Infineon  TLE9877       5V

    and  STM32F071RB     3.3V

    Voltage Levels:

    These are the Voltage thresholds we are working with

    Vcc2 on the mC side is set to the supply Voltage of the mC

    If it does not work to design the circuit for both mC's, I suppose it should be possible to design it only for 5V and then use a voltage level shifter.

    Thanks for your help

    Dustin

  • 0 in reply to Dustin Walker
    TI__Genius 17100 points

    Hi Dustin,

    Thank you for confirming this information. These input HIGH/LOW thresholds for TLE9877 and STM32F071RB look to be high enough to account for the external components required to achieve this bidirectional signal isolation path.

    The isolator is also capable of operating with Vcc1 = 5V and Vcc2 = 3.3V; as long as the Schottky diodes used have low forward voltages and Q1 is biased correctly, the only additional concern our team brought up is this: external components might limit the successful datarate. Resistors on the order of kilo-ohms will be needed to prevent damage to the isolator, which will also affect signal rise/fall times more than for I2C signals since this design is meant for datarates < 7MHz.

    This solution could still work for SWD, but the above disclaimer applies. Please let us know of any follow up questions.


    Respectfully,
    Manuel Chavez