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PWM pin tolerances on ADT7470 when the device is not powered

Question asked by ChrisP@hds on May 14, 2012
Latest reply on May 14, 2012 by jtowey

In a change to our current application, I'm required to power up the fans before the rest of the circuitry, including the ADT7470 device. The datasheet states that these pins are open drain outputs so to my mind there should not be an issue with the device not being powered and having a signal present at those pins, but I just need to check before the change gets implemented.

 

The fans I'm using are a 4-pin PWM fan which pulls the PWM signal to 4.5V, which could in theory, be powered up indefinitely without the ADT7470 being having its power applied.

 

I guess my question is, would having the PWM signals at the device pins without the device being powered up cause any damage to the device or create an odd behaviour?

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