Query Reagrading ADUM5402

Dear Team,

I am using ADUM5402 isolator in my design. I am giving 5V supply as the VDD & by pulling down the VSEL pin I am selecting VISO as 3.3V. Now I have few doubts:

1. I am using four isolator chips in my board, I have used same net name for all the 3.3V-ISO of four isolator chips. Any suggestion regarding this?

2. 3.3V-ISO is not driving any load, so for voltage regulation what resistor I have to place between 3.3V-ISO & ISO-GND for proper operation? from data sheet I figured out that I have to make IISO as at least 10mA for voltage regulation of 3.3V-ISO, so for four chip If I use the same net total IISO will be 40mA & I have to place a resistor between 3.3V-ISO & ISO-GND of value 3.3V/40mA to maintain the voltage regulation of 3.3V-ISO, please rectify me If I am wrong. Any suggestion will be appreciated.

Regards,

Sayantan

  • Sayantan: Answers to your questions:

    1. What is the reason for using 4 VISO with the same net name for all of the 3.3V-ISO?  A schematic may be best to explain.

    2. The current datasheet and version of the ADum540x does not require minimum 10mA Viso load, this was for previous version of the ADum540x and datasheet.

    Regards, Brian

  • Dear Brian,

    I am using four ADUM5402 for 8 channel RS 422 (Rx+Tx), that's why I provided same net name for all four VISOs.

    I am attaching the schematics for one ADUM5402 section, there are four such ADUM5402 section. I have one more query, shall I use one zener diode for 3.3V-ISO?

    Regards,

    Sayantan

  • Sayantan:  For your application, using multiple ADuM5402's, each ADuM5402 Viso needs to have its own net name, they can not all be connected together since each ADuM540x is a master, and can't be a slave, as described in Table 26 of the datasheet.

    What is the datarate and output capacitance for the channels on the 3.3V-ISO side? Depending on the datarate, it is possible that you do not need 4 ADuM5402's to provide the Viso current needed to provide the +3.3V-ISO current. For example, the ADuM5402 datasheet table 7 shows the IISO load typical supply current available from Viso at 1Mbps and 25Mbps data rates. In that case, you could use some ADuM1402's to provide the isolated channels, and use the ADuM5402 VISO voltage to supply the extra VDD2 supply for the ADuM1402's.

    Regards, Brian

  • Hi Brian,

    Thanks for your advice, I am using one ADUM5402 & three ADuM1402 as per the recommendation. I am suing this isolation for RS422, so 10MBps data rate is sufficient I think.

    Regards,

    Sayantan

  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:25 PM over 2 years ago
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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