How to use ADuM1250 with two isolated power supply 3.3V and 5V


I have a question on how to use ADuM1250 with two isolated power supply.

My customer has the following wiring.

 ・SDA1 & SCL1 are connected to VDD1 (3.3V)through a 10k resistor.

 ・SDA2 & SCL2 are connected to VDD2(5V) through a 10k resistor.

 ・CLK is always input from the CPU, DATA is bidirectional.

 ・GND1 and GND2 are isolated. 

In the above, is the circuit right?

  • 0
    •  Analog Employees 
    on Nov 27, 2019 6:55 PM 11 months ago

    Hi Zeno, 

    It doesn't sound like there is anything wrong with what you have described. I'll just point out a few details of the ADuM1250...

    • I'll assume bypass caps are not shown for simplicity (It is important to have them and keep them very close to the pins)
    • Level shifting from 3.3V to 5.0V is completely fine. VDD1 and VDD2 can be from 3.0V to 5.5V and are not required to be powered at the same voltage level.
    • 10k is may be a weak pull-up, depending on data rate and line capacitance it may need to be adjusted, Maybe its fine, just something to be aware of and verify on the scope that the rise times are appropriate.
    • Both the SDA and SCL channels are bidirectional on the ADuM1250.  
    • The ADuM1250 has different levels on both sides. Verify that the CPU (or whatever device is facing Side 1 of the ADuM1250 is tolerant of vil>=.09V