Figure 142. V5Ref_Sus With 5V_Always Connection Option; Figure 143. V5Ref_Sus With 3.3V_Always And Vcc5 Or Vcc5_Sus Connection Option - Intel 855PM Design Manual

Platform Power Delivery Guidelines
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
platform, then an alternative implementation using a 3.3V_ALWAYS (active S0-S5) and a V
S0-S1M) or V

Figure 142. V5REF_SUS With 5V_ALWAYS Connection Option

Figure 143. V5REF_SUS With 3.3V_ALWAYS and VCC5 or VCC5_SUS Connection Option

252
pins if available (see Figure 142). If such a supply rail is not readily available on the
(active S0-S3) rail can be used instead (see Figure 143).
CCSUS5
+V5ALWAYS
V5REF_SUS1
V5REF_SUS2 V5REF_SUS1
Intel
ICH4-M
ICH4-M
USB D+ USB D+
USB D- USB D-
V5REF_SUS2 V5REF_SUS1
Intel
ICH
-M
ICH4-M
4
USB D+ USB D+
USB D- USB D-
Note: D1 and D2 are BAT54 or Equivalent Schottky Diodes
0.1uF 0.1uF
Customer specific or Customer specific or
Intel recommended Intel recommended
USB interface USB interface
circuits circuits
+V5S or +V5
+V3ALWAYS
* * * *
D1 D1 D2 D2
0.1uF 0.1uF
Customer specific or Customer specif i c or
Intel recommended Intel recommended
USB interface USB interface
circuits circuits
®
Intel 855PM Chipset Platform Design Guide
R
(active
CC5
Customer specific or Customer specific or
Intel recommended Intel recommended
USB power circuit USB power circuit
USB Power (5V) USB Power (5V)
GND GND
Customer specific or Customer specific or
Intel recommended Intel recommended
USB power circuit USB power circuit
USB Power (5V) USB Power (5V)
USB D+ USB D+
USB D- USB D-
GND GND