VTI Instruments Metek EX1202 - Application Note; Overview; Ex12 X2 and Ex12 X6 Power Consumption Calculation

VTI Instruments Corp.
154 Appendix B
APPLICATION NOTE
OVERVIEW
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 EX1200 mainframes are provided which indicate
the limitations on the power supplies and the slots.
POWER SPECIFICATIONS
AVAILABLE POWER
1
EX1202/06/62/66
EX1208/68
120 W
120 W per segment, 360 W total
USEABLE POWER
1
EX1202/EX1206
EX1262/EX1266
EX1208/68 (Slots 1 – 5)
EX1208 (Slots 6 – 10)
EX1268 (Slots 6 – 10)
EX1208/68 (Slots 11 – 16)
115 W
110 W
102 W
97 W
102 W
102 W
*The EX12x8 mainframe is powered by four power supplies and each power supply is used for a finite number of mainframe slots. For more
information, see the Power Consumption in Appendix B.
MAXIMUM CURRENT PER RAIL
1,2
3.3 V 5 V 24 V
EX1202/EX1206
EX1262/EX1266
EX1208/68 (Slots 1 – 5)
EX1208/68 (Slots 6 – 10)
EX1208/68 (Slots 11 – 16)
6.00 A 13.420 A 3.320 A
6.00 A 13.410 A 3.074 A
14.99 A 13.582 A 2.950 A
14.99 A 13.362 A 2.950 A
14.99 A 13.355 A 2.950 A
MAXIMUM CURRENT CARRYING CAPACITY PER SLOT
3.3 V rail
5 V rail
24 V rail
6 A
3.75 A
1.6 A
Note
1
: The EX12x8 mainframe is powered by four power supplies and each power supply is used for a finite number of mainframe slots.
For more information, see the Power Consumption in Appendix B.
Note
2
: For more information on calculating power consumption, please refer to the Power Consumption in Appendix B.
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.
EX12X2 AND EX12X6 POWER CONSUMPTION CALCULATION
For the EX12x2 and EX12x6 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 EX12x2/x6 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.