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ISO7742: Looking for isolation devices

Part Number: ISO7742
Other Parts Discussed in Thread: ISO6741

Hello;

I have a design that requires some isolations; details are described as below. 

1. An UART interface (RX/TX signals, baud rate up to 1Mbit/s) and another digital sync signal X (switching at 1MHz, irrelevant to UART) , these signals need to be connected to another PCB which has completely different a power domain. Which isolation device would you recommend?

2. An USB port will be connected to a PC. Which isolation device would you recommend?

Thank you very much!

Wen Li

  • Hi Wen Li,

    Thanks for reaching out, please see my inputs below. Thanks.

    1. For your requirement of isolating UART signals of 1Mbps and a digital sync signal of 1MHz, you can use ISO6741. If you mean to say that the other PCB is powered by a different power rail but has same voltage level as the primary PCB then it shouldn't be a problem. Just make sure GNDs of the two PCBs are connected to each other.
    2. We currently do not have a device to support USB isolation.

    Regards,
    Koteshwar Rao

  • Hi Koteshwar Rao;

    Thanks for the info.

    The other PCB's power voltage will be different. Any advice? 

    Also what are the differences between ISO6741 and ISO774x device? We are looking for high-end ISO devices for future prove, such as better EMI, higher speed, etc. Cost is not a main concern here. Any other recommendation?

    Regards

    Wen

  • Hi Wen,

    The digital isolator has two power supplies pins VCC1 and VCC2. The supply pin that is connecting to the other PCB should have the same rail voltage to communicate reliably as the input signal threshold levels are input supply voltage dependent. If same voltage cannot be used then you might consider using a voltage level translator on either PCB to make them compatible.

    There are very minimal differences between ISO674x and ISO774x with ISO774x being slightly superior in performance. The major differences include lower datarate of 50Mbps, lower CMTI rating of 50kV/µs and lower isolation voltage ratings for ISO674x. If these specifications matter, then you can consider using ISO774x as well. Most EMC performances should remain the same between the two devices.

    ISO67xx and ISO77xx are our latest digital isolator family devices, hence I recommend choosing a device from either of these two families.Thanks.

    Regards,
    Koteshwar Rao