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ISO1640: ISO1640 could connect GPIO?

Lawrence He
Expert 2440 points
Part Number: ISO1640
Other Parts Discussed in Thread: ISO6742, ISO7742

Hi, Support Team

about below schematic, have any concern.

SDA2 and SCL2 could connect GPIO?

if any suggestion, Please advise me.

Thanks,

Best regards,

Lawrence

  • 0
    TI__Expert 8030 points

    Hi Lawrence, 

    We are currently looking into this and will get back to you on Monday. 

    Regards, 

    Kenneth

  • 0 in reply to Kenneth Arnold
    TI__Expert 8030 points

    Hi Lawrence, 

    Thank you for your patience.

    Here is my review of the schematic that you provided:

    -For the VCC1 decoupling capacitor (C194) in the schematic, I see that you have a ground node connected to this component that does not match the GND node connected to the GND2 pin of the ISO1640B. To maintain isolation, all components on the same side of the isolation barrier should share the same GND node, and this GND node should be different from the GND node connected to the components on the opposite side of the isolation barrier. If this is not done, isolation will not be maintained. Therefore, to maintain isolation, I recommend that you connect C194 to the same GND node that is connected to the GND2 pin (pin 5) of the device. 

    -Additionally, for the decoupling capacitors, another recommendation I have is that you consider using decoupling capacitors with capacitance values of 0.1 µF instead of 10 nF, since this is what we recommend in the device datasheet. Following this recommendation will help to ensure reliable device operation at all data rates. 

    Regarding your question, our recommendation is that you use the ISO1640B to isolate I2C signals. If the device in the schematic above is connected to a GPIO I/O with a configurable I2C module, and this module will be used to send and receive I2C signals, then this configuration is okay. However, if you are using the ISO1640B to isolate a generic GPIO signal that does not use a protocol (like I2C), then our recommendation is that you use a digital isolator instead (such as the ISO7742 or the ISO6742), since these types of these devices are designed specifically for this type of application. While the ISO1640B is capable of isolating GPIO signals, it is not recommended for these types of applications. When compared to a digital isolator, the ISO1640B has a higher low level output voltage on side 1, a lower max data rate, and it also uses an open-drain driver for the output. Therefore, if your application requires you to isolate a generic GPIO signal, I recommend that you use a digital isolator, such as the ISO6742 or ISO7742. If the schematic above will be used to isolate I2C signals that follow the I2C protocol, then I recommend that you continue to use the ISO1640B. 

    Regards,

    Kenneth