AD5420 IOUT PIN PROTECTION

Hi,

I have  Schottky diodes clamping to AVDD and GND and a 22ohm series resistor for protecting the IOUT pin of AD5420.

In spite of this additional circuitry, the part got destroyed when someone connected 24V between the current loop output terminal and Ground.

Can anyone please suggest a reliable protection scheme?

Thanks,

JayantD

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    •  Analog Employees 
    on Aug 8, 2018 11:30 AM

    Hi Jayant.

    If the 24V is connected to 4-20mA connector, that voltage is directly connected to the 250Ω load. That would generate a current of 96mA. That is about 2.3W of power dissipation on the load. can you check if it could handle that power?

    What is the status of the FAULT pin? If the load is damaged by the high power dissipation and is now an open circuit, you should see the fault pin to be pulled low.

    In selecting the protection diodes and the current limiting resistor, you have to consider their power ratings so that they would be able to handle the power due to the over voltage (transient). Failing to do so, the AD5422 will also fail after the diodes are damaged.

    Best regards,

    Rainier 

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  • 0
    •  Analog Employees 
    on Aug 8, 2018 11:30 AM

    Hi Jayant.

    If the 24V is connected to 4-20mA connector, that voltage is directly connected to the 250Ω load. That would generate a current of 96mA. That is about 2.3W of power dissipation on the load. can you check if it could handle that power?

    What is the status of the FAULT pin? If the load is damaged by the high power dissipation and is now an open circuit, you should see the fault pin to be pulled low.

    In selecting the protection diodes and the current limiting resistor, you have to consider their power ratings so that they would be able to handle the power due to the over voltage (transient). Failing to do so, the AD5422 will also fail after the diodes are damaged.

    Best regards,

    Rainier 

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