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Latchup with ADUM1251

Question asked by PKrown on Nov 6, 2012
Latest reply on Nov 9, 2012 by MSCantrell

We have a design where we use ADUM1250 to isolate I2C. The data sheet implies this part is suitable for hot-swap. When we unplug and reconnect our peripheral board, we latch up most of the time (I2C activity on the host side does not appear on the peripheral side (PCF8575), SDA and SCK lines stay high (but I can pull down with a test resistor)). Disconnecting and reconnecting the power connector eventually gates us working. I tried changing to an ADUM1251 (unidirectional on the SCK line), which improved things, but I still latch up about 1 in 20 disconnect-reconnect cycles. When I latch up I get the same symptom as before (both lines on the downstream (SDA2 and SCK2) side stay high (despite the SCK being unidirectional)). This leads me to assume that we are latching up in the "Startup" mode rather than the data direction control latching up. Host side data appears to be meeting the "low" threshold of the device. We are not doing anything exotic, supply on both sides is 5v. Given that this part is claimed to be "free of any glitches or lock up (AN-913)) any suggestions as to what is going on?

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