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ADM6316 !MR Input

Question asked by craigl on Aug 24, 2011
Latest reply on Aug 29, 2011 by paul.osullivan

I'm using an ADM6316DZ26ARJZ-R7 on a new board I've designed and it's not behaving as I exptected.



The board is for a voice communications product that is solar powered and is installed in relatively remote areas.

It's important the board operate reliably and recover automatically from 'glitches' or be forced to recover by a 'host' or companion processor (in the form of a GSM/3G wireless module for this product) ..... I wanted the MCU to be able to force a complete power cycle of itself and associated circuitry if it determined some peripheral device wasn't responsive or if requested by the host device.


I've set it up so the watchdog input is driven by an I2C port expander so if I have an I2C lockup, the watchdog won't get polled and the ADM6316 reset output will disconnect power from the MCU subsystem for > 1 second allowing things to restart.  I have other devices on the I2C bus that must be contactable at all times.


I also wanted an instant power cycle option so I connected one of the MCU pins to the !MR input (via 1k resistor).  I have an external 100K pullup and the MCU at reset configures all IO pins as high Z inputs.  The ADM6316 also has approx 60k pullup on !MR.


The problem...

With this configuration, as soon as power is applied, the ADM6316 Reset output is asserted (ok).  I then see activity on the !MR input that looks like data (but can't be) - the input toggles between being high (approx 2.8V) and low (0V) for a while then stops pulsing and returns high.  The Reset output stays asserted the entire time.  If I tie the !MR input to 2.8V, the Reset line de-asserts.  If I remove the connection between the MCU and ADM6316, the device operates properly.  I watched the MCU pin while the !MR input was pulsing and there was no activity at all - it remained at 2.8V (logic supply rail).


It's not critical that I have an instant power cycle option but I would like to know what's going on.


Thanks in advance