Hardware Reference
In-Depth Information
I/O is operated from a 250 W power supply and that the load on the various
supply rails is as follows:
Supply rail (V)
Load (max) (A)
Power (W)
+
3.3
15
50
+
5
3
1 5
−
5
0.5
2.5
+
12
7
84
−
12
0.5
6
+
5 standby
1.5
7.5
Total power:
165 W
Remaining power available:
250
−
165
=
85 W
Supply rail distribution
In order to minimize supply-borne noise and glitches, the following recommen-
dations should be observed when considering the design and layout of prototype
expansion cards:
1 Ensure that the ground/common 0 V foil is adequate and that the three ground
connections (B1, B10, and B31) are linked together via a substantial area of
copper foil.
2 Include decoupling capacitors on each of the supply rails as follows:
(a) 100
µ
F axial lead electrolytic to decouple the
+
5 V rail (locate close to
pins B1 and B3 or B29 and B31).
(b) 47
µ
F axial lead electrolytic to decouple the
+
12 V rail (locate close to
pins B9 and B10).
(c) 47
µ
F axial lead electrolytic to decouple the
−
12 V rail (locate close to
pins B7 and B10).
(d) 10
µ
F axial lead electrolytic to decouple the
−
5 V rail (locate close to
pins B5 and B10).
(
Note
: Capacitors can be omitted when the relevant voltage rail is not used
within the expansion card.)
3 Fit 10
µ
F 16 V radial lead decoupling capacitors to the
+
5 V rail at the rate of
one capacitor for every eight to ten TTL or CMOS logic devices. Capacitors
should be distributed at regular points along the supply rail.
4 Fit 100 nF 16 V disk ceramic capacitors to the
+
5 V rail at the rate of one for
every two to four TTL or CMOS logic devices. Capacitors should be placed at
strategic points close to the supply pin connections of the integrated circuits.
5 Fit one 10
µ
F 16 V and one 100 nF 16 V capacitor to the
+
5 V rail for each
VLSI device. Capacitors should be placed as close as possible to the supply
pin connections of the devices in question.
6 Repeat (3), (4), and (5) for each of the other supply rails (where used).
Finally, it should go without saying that one should never attempt to insert or
remove an expansion or adapter card when the power is connected and the system
is running. Failure to observe this precaution may result in serious damage not
only to the card in question but also to other cards that may be installed as well
as to components on the system motherboard. If this all sounds rather obvious,
