User`s guide

Elan Digital Systems Ltd. 45 AD125 USER’S GUIDE
7. OPERATIONAL PRECAUTIONS
Unless otherwise stated, all voltage levels are referenced to the AD125’s DIGITAL GROUND PIN.
• Don’t leave active signals connected to the digital IOPINS that are
capable of sourcing more than a few mA whilst the AD125 itself is
unpowered. This could lead to “reverse powering” the card via its
inputs which can cause latch-up and destruction of internal cmos
devices. If there is a possibility of this condition occurring, you are
advised to connect series resistors between your drivers and the
AD125’s inputs to affect current limiting (typ 4k7). Remember that
this will slow the edges of the digital signals.
• Don’t draw excessive current from Vcc, +15V or -15V. The limit is
shown in the pinout table. Doing so will adversely effect the
AD125’s performance and could cause damage.
• Avoid connecting “analogue ground” and “digital ground” together.
Inside the AD125, a connection between these two is made at a
single “star point” to help reduce digital ground noise coupling into
the analogue sections. If you can, keep the two returns separate in a
similar fashion on your equipment.
• The 32 way IO connector is quite delicate. Don’t stress it unduly.
• Don’t apply analogue signals to the An inputs which are greater than
35v. Levels above this will damage the AD125 card.
• Don’t apply digital inputs to the AD125 that are greater than (system
Vcc + 0.5v) where “system Vcc” is the level provided on the
AD125’s Vcc output pin. Doing so will damage the AD125.
Likewise, don’t apply levels that are less than -0.5v to the digital
inputs.
• Don’t short circuit any of the AD125’s outputs to ground or to other
outputs. This will damage the AD125.
• Ensure that the card’s main 5v power input on the pcmcia 68 way
connector does not exceed 7.0v as this will damage internal devices.
This is normally not a factor that the user of a “standard” pcmcia slot
needs to consider. However, under fault conditions or an embedded
design this condition may need to be given some thought to avoid
damaging the AD125.