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ISOW7841: Isolators getting extremely hot, VISO is exceeding 5.5V, unstable

Part Number: ISOW7841

Hello, I am trying to prototype the use of ISOW7841 by using SPI from a "master" Arduino to an external, SPI interface ADC connected to 3.3V of a 2nd Arduino. For whatever reason, the chip starts getting ridiculously hot after the initial 5min of operation, and I notice the voltage at VISO going high. I have wired as shown in the attached drawing. Any ideas? I know I don't have the decoupling caps, but would this really affect the DC-DC converter in such a negative way? This chips are expensive (~$10)  and I feel like I've already destroyed 2 :/

Also just to note, the voltage from VISO to GND2 when the master Arduino in not connected is around 2.3V which I find curious. 

  • Hi William,

    Welcome to the E2E forums! Thank you for posting these helpful details and drawings.

    Yes, the decoupling caps must be connected to both Vcc and Viso of the ISOW7841 - this is precisely why the Viso voltage is about 2.3V when floating as you can read on this post. Because of the ISOW7841's power supply feedback operation, we recommend that the decoupling capacitors on Vcc exceed the capacitors on Viso by at least 100uF. This is stated in Section 11 - Power Supply Recommendations of the ISOW784x datasheet.

    Including decoupling capacitors as mentioned above should be the solution for you, but in cases where Viso continues to exceed 5.5V, external components can help regulate Viso (like Zener diodes) or reset the ISOW7841, as detailed in the Overvoltage protection for isolated DC/DC converter Tech Note. Please also ensure that both GND1 pins of the ISOW7841 are connected together and both GND2 pins are connected together.


    Do let me know if it's possible to implement these solutions! I will await your response.


    Thank you for your time,
    Manuel Chavez

  • Thank you, I will order those caps from DigiKey and let you know how it goes.

    Will