[net.micro.amiga] Logical Death by Power Starvation

hull@hao.UUCP (Howard Hull) (08/15/86)

Yes, there is something different about powering up compared to powering
down.  In the days of memory chips that had multiple power supply voltage
pins, designers (DEC on LSI11's, for instance) began to discipline their
power supply systems by including IC op-amp integrators to control the
ramp-up rates of various power supplies.  Specifications for various chips
required that some voltages "stay ahead" of others on ramp-up.  In multiple
power supply systems this was very beneficial, even for chips that didn't
have multiple power pins, as it kept input signals and output load returns
proportionally between the rail voltages and prevented blasting the on-chip
clamp diodes.

The best that could be done on power-down was to place over-clamp diodes
between the most positive supply and any lesser-voltage supplies (anode
connected to the lesser voltage supply).  Similarly, diodes could be used
for negative-going supply sets (anode connected to most negative supply).
As a consequence, on power-down, even though voltages are kept between the
major rails, proportionalities between supplies are not preserved, and logic
is sometimes perverse; particularly when the switch bounces or power rebounds
and then croaks (as during a pre-failure brown-out).
								Howard Hull
[If yet unproven concepts are outlawed in the range of discussion...
                   ...Then only the deranged will discuss yet unproven concepts]
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