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For the AD5421: If there is no loop power applied, and yet there are voltages on the digital pins, can there be damage to the AD5421?

Question asked by artg on Jun 11, 2016
Latest reply on Jun 15, 2016 by clon

We are using an AD5421 to construct a 4-20 mA loop. The overall architecture we have have includes the use of a microprocessor to communicate with the AD5421 through its SPI port. Originally we were powering the microprocessor with DVDD. However we found the loop couldn't source the full required current. We then powered the microprocessor with a different power supply. This supply also supplies voltage to RANGE1, RANGE2, ACD, REGSEL0, REGSEL1, and REGSEL2. In addition the microprocessor will have signals for the SPI port, SYNC, and LDAC pins.

 

Now, with this arrangement, the loop power is provided by an independent power supply. Operationally, we can have the microprocessor powered, while there is no loop power. Under this condition, there are voltages on the digital input pins mentioned above. Can the existence of the voltages - again, with no loop power - cause damage to the AD5421 by violating the Absolute Maximum ratings for these pins because there is no loop power?

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