VTI Instruments Corp.
158
A
PPLICATION
N
OTE
O
VERVIEW
As with any backplane-based system where modules share power, such as VXI and PXI, the
possibility exists where a combination of plug-in modules may exceed the maximum power
available from the power supply. There are two limitations that govern power delivery by a
supply: 1) the maximum power of the power supply and 2) the maximum power that can be
delivered to a single slot. To avoid potential power-related issues, these two limitations cannot be
exceeded.
As a reference, the power specifications for the EX1200A mainframes are provided which indicate
the limitations on the power supplies and the slots.
P
OWER
S
PECIFICATIONS
A
VAILABLE
P
OWER
1
EX1202A/06A
EX1208A
120 W
1000 W
U
SEABLE
P
OWER
1
EX1206A
EX1266A
EX1208A
EX1268A
101.48 W
95.53 W
976.48 W
970.53 W
* For more information, see the
M
AXIMUM
C
URRENT
P
ER
R
AIL
1,2
3.3 V
5 V
24 V
EX1202A
EX1262A
EX1206A
EX1266A
EX1208A
EX1268A
3.00 A
13.08 A
3.17 A
3.00 A
13.07 A
2.92 A
3.00 A
12.88 A
3.17 A
3.00 A
12.87 A
2.92 A
40.00 A
36.00 A
29.02 A
40.00 A
35.99 A
28.77 A
Note
1
: For more information, see the
in
Note
2
: For more information on calculating power consumption, please refer to the
Note
3
: These values indicate the maximum current provided by the power supply. This value is limited by the carrying capacity for that rail. See
the
Maximum Current Carrying Capacity per Slot
specification for more information.
M
AXIMUM
C
URRENT
C
ARRYING
C
APACITY
P
ER
S
LOT
3.3 V rail
5 V rail
24 V rail
6 A
3.75 A
1.6 A
EX1206A
AND
EX1208A
P
OWER
C
ONSUMPTION
C
ALCULATION
For the EX1206A and EX1208A mainframes, the total power useable (
P
USEABLE
) between the
3.3 V (
P
3.3V
), 5 V (
P
5V
), and 24 V (
P
24V
) rails is defined by the
Useable Power
specification for
the mainframe being used. These mainframes are powered by a single power supply and current
on the 3.3 V rail is derived from the 24 V rail with an efficiency of 80%. When calculating the
total power consumption of the cards installed in an EX1206A mainframe, the following
conditions must be satisfied:
1)
P
24V
+ P
5V
+ P
3.3V
≤
P
USEABLE
2)
P
24V
+ P
3.3V
≤
84 W
3)
P
5V
≤
75 W
4)
P
3.3V
≤
24 W
5)
No rail can exceed the maximum current per rail. Particular attention should be paid to the
24 V rail.
For example, an EX1206A is populated with the following three cards:
Summary of Contents for Ametek EX1200A Series
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