82371AB Datasheet, PDF (41/284 Pages) Intel Corporation – PCI-TO-ISA / IDE XCELERATOR PIIX4

E
82371AB (PIIX4)
2.3. Power Sequencing Requirements
There are no power sequencing requirements for the various VCC power supplies to PIIX4. The VREF signal must
be tied to 5V in a system requiring 5V tolerance. In a 5V tolerant system, this signal must power up before or
simultaneous to VCC. It must power down after or simultaneous to VCC. In a non-5V tolerant system (3.3V only),
this signal can be tied directly to VCC. There are then no sequencing requirements. Refer to Figure 2 for an
example circuit schematic that may be used to ensure the proper VREF sequencing.
Vcc Supply
(3.3V)
5V Supply
1k _Ω
1µF
To System
VREF
To System
Figure 2. Example VCC5REF Sequencing Circuit
Pix4_01
PRELIMINARY
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4/9/97 2:23 PM PIIX4aDS
INTEL CONFIDENTIAL
(until publication date)