Product specifications

Design Guide - VT82C694X Apollo Pro133 with VT82C686A
Preliminary Revision 0.5, November 19, 1999 71 Motherboard Design Guidelines
Technologies, Inc.
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2.5.7.2 STR Power Plane Control
VT82C686A controls the system entering the various suspend states through the suspend control signals listed in Table 2-14.
Three power plane control signals (SUSA#, SUSB# and SUSC#) are provided to turn off more system power planes as the system
moves to deeper power-down states from normal operation to POS (only SUSA# asserted), to STR (both SUSA# and SUSB#
asserted), and to STD (all three SUS# signals asserted).
Table 2-14. Resume Events Supported in Different Power States
Power State RSMRST# SUSST1# SUSA# SUSB# SUSC#
On
1 0 1 1 1
POS
1 0 0 1 1
STR
1 0 0 0 1
STD / Soft-off
1 0 0 0 0
Mechanical off
0 0 0 0 0
Upon initiation of suspend, VT82C686A will assert the SUSST1# and SUS[A:C]# signals in a plane defined sequence to switch
the system into the desired power state. The SUSA#, SUSB# and SUSC# signals can be used to control various power planes in
the system. For example, SUSC# is typically connected to PS-ON (pin 14) of the ATX power supply connector through an
inverter to control the remote-off function.
Figure 2-63 shows an application circuit example on STR power plane control. When SUSB# is not asserted, Q1 is turned on and
Q2 is turned off. And V_DIMM power source is supplied by VCC3 in normal operation. When SUSB# is asserted, Q1 is turned
off and Q2 is turned on. And V_DIMM power source is supplied by 3V3SB (3.3V suspend power) during STR state.
R2
4.7K
+12V
D
Q
Q
C
P
AHCT74
-SUSB
-SUSC
Notes:
1. Components U1, U2, U3 and U4 are powered by +5V standby power source.
2. V_DIMM represents the power source to DIMM modules.
3. R
DS(ON)
of Q1 (N-channel MOSFET) should be as low as possible. RDS(ON)= 0.008 ohm at VGS=10V for FDS6670A.
U4
-RSMRST
PW_GOOD
1
3
2
4
6
5
1
3
2
1
3
2
3V3SB
V_DIMM
NDC632P
P-MOSFET
Q2
VCC3
Q1
FDS6670A
N-MOSFET
U1A
U1B
AHC00
AHC00
U2A
U3A
AHC08
AHC32
D
G
S
DS
G
R1 1K
Q3
MMBT3904
Figure 2-63. STR State Power Plane Control Application Circuit
Note that these signals are associated with a particular type of suspend mode and power plane for descriptive purposes in this
section. Using these signals, the system designer can control any type of function desired.