1. Board Design > Power Management
12
Tsi382 (BGA) Evaluation Board User Manual
60E2010_MA001_03
Integrated Device Technology
www.idt.com
1.4.2.2
PCI
The PCISIG defines the power rules regarding PCI cards as a maximum of 25 Watts per card (All
power rails combined power draw). The individual current limits on voltage rails are included in
Table 5
.
It is not possible to provide the full power required to the PCI bus without violating the specification
while drawing power from only a x1 PCIe system. Up to 23W not including regulator efficiency losses
can be made available. The evaluation board provides the power requirements in one of two ways
depending on the application:
•
PCIe system power
•
ATX System connector
The following conditions summarize the power available for a single PCI card without external supply.
An efficiency of 85% is taken into account for switching regulators. These limits can be exceeded in
cases where the system can provide more than the suggested limit, which is usually only implemented
in hot swap systems.
For additional slots, or in cases where the system cannot supply enough power, a separate ATX power
connector is used to power the card. The evaluation board senses the presence of this supply, and
disables the slave PCIe slot power. For the case of a separate external ATX supply, all four slots are
provided with the required power.
Table 5: PCI Connector Current Limits
Rail
Current
3.3V
7.6A
5V
5A
-12V
100mA
12V
500mA
Table 6: PCI Connector Current Limit with No External Supply
Rail
Supplying Topology
Current (Maximum)
3.3V
12V to 3.3V regulator
6A
12V
12V directly
500mA
-12V
N/A
N/A
5V
12V to 5V regulator
4A
