I am having problems with spikes on the +5V rail causing the 1232 to reset. Can
you please advise what the limits are for this pin.
The ADM1232 reset threshold is specc’d under TRIP POINT on the datasheet, the
user can set a 10% threshold or a 5% threshold. The minimum threshold is 4.25V
and 4.5V respectively.
Narrow pulses of as short as 10ns may be enough to trip the reset circuit. But
this will depend on the shape of the pulse as well as it’s duration.
From a practical point of view, the best solution may be filter the spikes you
are seeing on VCC with additional small value capacitors. For decoupling it’s
good practice to use 2 or 3 capacitor values in parallel with around 2 decades
between their values. 10uF, 100nF, 1nF for example. The small value caps will
be much better at taking out the high frequency components of the spikes.
The alternative is switch to a reset generator with a lower reset threshold.
Remember also that you digital logic may be sensitive to narrow spikes you are
seeing on VCC as well.