Question
The data sheet implies a source current of 800uA from the reset pin, the implication being that this is a weak pull-up against which the processorprogramming interface can pull the line low. This is the basis for our design.
Our problems arose during a recent production run when the programming interface could not pull the reset line low. We measured the pull-downcurrent on two such boards and measured 75mA! We then measured the pull-down current on three older cards that were programmed OK and even thenmeasured 18mA to 20mA.
The attached document contains a snapshot of our results; this shows two different camps for the devices we characterized. Both sets are way inexcess of 800uA, so what does the 800uA actually refer to?
The product in which this chip is used has been in production for a number of years and only recently have we had this high-current problem. Hasthere been a change to the ADM705 recently?
The 18-20mA we can live with. 75mA causes a problem.
Answer
ADM705's silicon was revised back in 2009.During the revision the output driving strength has been improved.
The RESET output driving strength specification on the data sheet states that with source current of 800uA, the output is guaranteed to be aboveVcc-1.5V. This remains true on the new silicon, thus the device performance is still in compliance with data sheet specification.There is never amaximum specification on the output driving strength.
If you want to make the output weaker, a series resistor can be used. Or else, the processor can pull down on the MR input instead of the RESEToutput.