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Maxim > Design Support > Technical Documents > Application Notes > Hot-Swap and Power Switching Circuits > APP 3605
Maxim > Design Support > Technical Documents > Application Notes > Oscillators/Delay Lines/Timers/Counters > APP 3605
Keywords: PCI,Express,hot-swap,hot-plug,hot-removal,graphics,add-
in,adapter,card,PC,inrush,current,power,x16,150W-ATX,current,limit,soft-start,ORing,ideal,diode,PCI-
SIG,specification,management,latched,auto-retry,auto-restart,Firewire,video
APPLICATION NOTE 3605
Power-Supply Management Solution for PCI Express
x16 Graphics 150W-ATX Add-In Cards
By: Dwight Larson, Senior Member of the Technical Staff
Sep 23, 2005
Abstract: The PCI Express x16 Graphics 150W-ATX Specification establishes detailed power-supply
management requirements for PC-graphics add-in cards. Designing a discrete solution to satisfy these
requirements can add considerable cost and complexity to the overall card design.
This application note describes how to use the MAX5943 integrated current limiter and the MAX5944 low-drop
power-supply ORing switch controller to enable a small, simple, low-cost power-management solution for PCI
Express 150W graphics cards.
The Specification
PCI Express is the next revolution in graphics add-in card-interconnect standards. This specification,
significantly increases bandwidth between the central processing unit (CPU) and graphics processing unit
(GPU) by enabling a balanced distribution of bandwidth to those applications that require it the most. The PCI
Express x16 Graphics 150W-ATX Specification provides additional electrical power for PCI Express graphics
beyond that supported by the existing PCI Express x16 specifications. The new maximum power levels
supported by this specification are 25W (low-profile card), 75W (standard size), and 150W.
A PCI Express x16 Graphics 150W-ATX add-in card can draw a maximum of 75W through the standard
connector, as specified in PCI Express CEM 1.1. Up to 75W additional power is provided through a 6-pin wire-
to-board connector. Therefore, the maximum total power that must be provided to a PCI Express x16 Graphics
150W-ATX add-in card is 150W.
A PCI Express x16 Graphics 150W-ATX add-in card must adhere to strict power-distribution, power-up, and
power-consumption requirements. To ensure safe operation and compatibility with noncompliant installations,
the following power-management requirements must be met:
The +12V delivered from the standard x16 connector and the additional +12V delivered from the
dedicated 6-pin power-supply connector must be treated as coming from two separate system power-
supply rails.
The two +12V input potentials must not be electrically shorted at any point on a PCI Express x16
Graphics 150W-ATX add-in card.
No specific power sequencing between the slot and 6-pin connector can be assumed. A PCI Express
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