Power Budgeting - HP 743 Series Technical Reference Manual For Oems

Power Budgeting

If your workstation's application requires several accessory cards and mass storage devices,
power budgeting may be required. Power budgeting ensures that the power needed for the
following internal devices does not exceed the power available:
• Mass storage devices
• Model 743 and Model 744 VMEbus Board Computer(s)
• Standard internal printed circuit boards
• PCI, PMC, VME, or EISA accessory cards
The Model 748 ruggedized workstation uses two power supplies. Each power supply pro-
vides voltages to the workstation's modules and accessory card slots as listed in Table 6-8
and Table 6-9.
These tables are also worksheets to use in determining your power budget. You may photo-
copy these tables as needed.
To determine the workstation's power needs, follow these instructions:
1 Determine the board computer's current requirements from the Computer Current Re-
quirements Worksheet (Table 6-5 or Table 6-6).
2 To determine the maximum current usage of the Model 744 memory cards, use Figure 6-
5 and Table 6-3 (for Model 744/132L) or Table 6-4 (for Model 744/165L). Note that some
memory cards draw current from +12V on the Model 744/165L. This is because +12
is converted to +5MEM for the 16MB, 32MB, and 64MB cards (seeFigure 6-2). You must
work with the worst case power draw to correctly determine power usage. Determine worst
case power draw by examining active memory bank configurations, using the following
steps:
a Examine your memory card configuration, noting which size card is in each memory
slot.
b The worst case active memory bank configuration depends on the slot position of the
memory cards, and the size of the cards. The 32 MB memory card has two banks per
card, and the 16, 64,128, and 256 MB cards each have only one memory bank per card.
• When 32 MB cards are used as a pair in memory slots 2 and 3 they can use three
memory banks concurrently.
• When used as a pair in slots 0, 1, or 2, the 32 MB cards can have two active memory
banks.
• The 16, 64, 128, and 256 MB cards each have only one memory bank that is active
at any one time.
The worst case power draw is when your system has two 32MB cards in slots 2 and 3
(these banks would be considered active, all other memory cards/banks would be con-
sidered inactive). The next worst case is a 256 MB card in any slot (all other memory
cards in the system would be inactive), followed by a 64 MB card in any slot (all other
memory cards in the system would be inactive), followed by two 32 MB cards in slots
0, 1, or 2 (all other memory cards in the system would be inactive), followed by a 128
MB card in any slot, and finally a 16 MB card in any slot (all other memory cards in
the system would be inactive).
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Power Requirements
Power Distribution
6-7