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#### MildInductor

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##### AD8232 AFE Fault Condition Protection
« on: May 20, 2024, 12:38:20 pm »
Hello, I am looking at the example circuit layouts for the AD8232 AFE. I see that current-limiting resistors are used in series to the electrodes to protect the patient from a fault condition where over 10uA runs through the electrodes. As a thought exercise I am trying to think of a relatively 'foolproof' topology for ensuring that the chance of a 10uA current running through the electrodes is almost 0%. Assume that the AD8283 is powered solely from a 9v battery. Also assume that the current-limit series resistors fail (completely short) and that the AD8283 has some sort of internal failure where the 9v battery rails are shorted to some combination of the electrodes. Although I realise that something would have had to have drastically gone wrong for both failure conditions to occur, I am wondering what another line of protection could be? Perhaps a resistor in series with the 9v battery to limit the current flow to the whole circuit. But then wouldn't limiting the whole circuit to 10uA of current flow be shortsighted, especially if you were to add other ICs in the mix. What other options are there? Some sort of current limiting circuit?

#### whoopigoldberg

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##### Re: AD8232 AFE Fault Condition Protection
« Reply #1 on: June 04, 2024, 05:17:39 pm »
Hello, I am looking at the example circuit layouts for the AD8232 AFE. I see that current-limiting resistors are used in series to the electrodes to protect the patient from a fault condition where over 10uA runs through the electrodes. As a thought exercise I am trying to think of a relatively 'foolproof' topology for ensuring that the chance of a 10uA current running through the electrodes is almost 0%. Assume that the AD8283 is powered solely from a 9v battery. Also assume that the current-limit series resistors fail (completely short) and that the AD8283 has some sort of internal failure where the 9v battery rails are shorted to some combination of the electrodes. Although I realise that something would have had to have drastically gone wrong for both failure conditions to occur, I am wondering what another line of protection could be? Perhaps a resistor in series with the 9v battery to limit the current flow to the whole circuit. But then wouldn't limiting the whole circuit to 10uA of current flow be shortsighted, especially if you were to add other ICs in the mix. What other options are there? Some sort of current limiting circuit?
Indeed, providing a backup line of protection to ensure that even if both the current-limiting resistors and the internal failure of the AD8232 AFE fail, the patient is still protected from excessive current flow through the electrodes is a wise decision.

Your initial notion of connecting a resistor in series with the 9V battery to limit the current flow to the entire circuit is sound. However, as you pointed out, restricting the entire circuit to 10uA of current flow may be overly restrictive. Instead, you may take a more flexible approach.

Smf