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Platform Power Delivery Guidelines
R
252
Intel
®
855PM Chipset Platform Design Guide
requires host controllers to withstand a continuous short between the USB 5-V connector supply to a
USB signal at the connector for an unspecified duration of time. Also, the USB 2.0 specification
requires a host controller to withstand a short between the USB 5 V connector supply to a USB signal at
the connector for 24 hours. The recommendation is to provide a 5V_ALWAYS (active S0-S5) supply to
the V
5REF_SUS
pins if available (see Figure 142). If such a supply rail is not readily available on the
platform, then an alternative implementation using a 3.3V_ALWAYS (active S0-S5) and a V
CC5
(active
S0-S1M) or V
CCSUS5
(active S0-S3) rail can be used instead (see Figure 143).
Figure 142. V5REF_SUS With 5V_ALWAYS Connection Option
+V5ALWAYS
USB D+
V5REF_SUS1
V5REF_SUS2
USB D-
ICH4-M
USB Power (5V)
GND
Customer specific or
Intel recommended
USB interface
circuits
Customer specific or
Intel recommended
USB power circuit
0.1uF
USB D+
V5REF_SUS1
USB D-
Intel
ICH4-M
USB Power (5V)
GND
Customer specific or
Intel recommended
USB interface
circuits
Customer specific or
Intel recommended
USB power circuit
0.1uF
Figure 143. V5REF_SUS With 3.3V_ALWAYS and VCC5 or VCC5_SUS Connection Option
Note: D1 and D2 are BAT54 or Equivalent Schottky Diodes
+V5S or +V5
+V3ALWAYS
USB D+
V5REF_SUS2
USB D+
USB D-
ICH
4
-M
USB D-
USB Power (5V)
GND
Customer specific or
Intel recommended
USB interface
circuits
D2
*
0.1uF
Customer specific or
Intel recommended
USB power circuit
D1
*
USB D+
V5REF_SUS1
USB D+
USB D-
USB D-
USB Power (5V)
GND
Customer specific or
Intel recommended
USB interface
circuits
D2
*
0.1uF
Customer specific or
Intel recommended
USB power circuit
D1
*
Intel
ICH4-M