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Original question:

ISOW1432: ISOW1432 Vdd range for PROFIBUS MODE

ISOW1432: Vio=3.3V & VDD=5V operating conditions and Visoout = 3.3V possible?

user4991603
Prodigy 170 points
Part Number: ISOW1432
Other Parts Discussed in Thread: ISOW1412

Hello,

in regard to the linked question I want to add that on page 11 in the datasheet it says that Visoout can be 5V with VDD=VIO=3.3V.

https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/1136253/isow1412-isow1412-vs-isow1432

Furthermore, I would like to know the operating conditions for the case Vio=3.3V and VDD=5V.

With VDD = 5V can Visoout also be regulated down to 3.3V by the internal regulator?

Best regards,

Stephan

  • 0
    TI__Expert 8030 points

    Hi Stephan,

    From the information you have shared in your post, it sounds like you want to operate the ISOW1412 with the following configuration: VDD = 5V, VIO = 3.3 V, and VISOOUT = 3.3 V. If this is not the case, please let me know.

    Yes, it is possible to operate the ISOW1412 with this configuration (VDD = 5V, VIO = 3.3 V, and VISOOUT = 3.3 V). When VDD = 5V, VISOOUT is capable of outputting 3.3V, provided that EN/FLT pin is set to a logic high or left open, and the MODE pin is shorted to GND2 or left floating. This configuration is explicitly mentioned as a valid configuration by Table 10-1 in the device datasheet (see table below). 

    If you have any further questions, please let me know.

    Regards,

    Kenneth

  • 0 in reply to Kenneth Arnold
    Prodigy 170 points

    Dear Kenneth,

    to be honest, we are not sure yet if we are going to use 5V or 3.3V on the secondary side.

    Therefore, I placed two 0 Ohm resistors on the mode pin, one that goes to GND2 and the other one goes to Visoout.

    Because the design works with 3.3V logic levels I choose to power VIO with 3.3V and I choose to power VDD with 5V to be able to select between 3.3V and 5V for Visoout and I wanted to remark that the datasheet doesn't have a operating characteristics table for this combination.

    I also remarked that the datasheet presents contradictory information for the case where VDD=3.3V.

    Therefore, have a look at the screenshot I made of page 11 on my first post. The lower row implies that Vsioout = 5V should work with VDD=3.3V.

    I now know that it doesn't work but I just wanted to let you know.

    Best regards,

    Stephan

  • 0 in reply to user4991603
    TI__Expert 8030 points

    Hi Stephan,

    user4991603 said:
    Because the design works with 3.3V logic levels I choose to power VIO with 3.3V and I choose to power VDD with 5V to be able to select between 3.3V and 5V for Visoout and I wanted to remark that the datasheet doesn't have a operating characteristics table for this combination.

    I believe that the electrical characteristics table that you referenced in your initial post (Section 8.8 in the device datasheet) is specifically kept generic so that it can be applied to all supported voltage configuration combinations of the device. All parameters that are dependent on either VIO or VISOIN specifically reference the levels that these voltages are at for the characterized device specification. We do not expect the values of these electrical characteristics to change depending on the values of VDD and VISOOUT, which is why we do not provide a separate table for different configurations. If certain specifications in this table do not mention any set voltage values for any of the device voltage configuration pins (such as VDD, VISOOUT, or VIO), then it is because the specifications can be applied for all supported voltage configuration levels of the device.

    user4991603 said:

    I also remarked that the datasheet presents contradictory information for the case where VDD=3.3V.

    Therefore, have a look at the screenshot I made of page 11 on my first post. The lower row implies that Vsioout = 5V should work with VDD=3.3V.

    Thanks for providing clarification on this. I now see how the configuration of the table may lead to come confusion on what VDD and VISOOUT configurations are supported by the device. As shown by my previous post, VDD = 3.3V and VISOOUT = 5V is not a supported configuration by this device. I will make a note to revise this section for future datasheet revisions so that this is made more clear. Thank you for bringing this to our attention.

    Regards,

    Kenneth