LPC47M172-NR SMSC [SMSC Corporation], LPC47M172-NR Datasheet - Page 135

• Manufacturer Part Number: LPC47M172-NR
• Description: ADVANCED I/O CONTROLLER WITH MOTHERBOARD GLUE LOGIC
• Manufacturer: SMSC [SMSC Corporation]

7.31.2 5V Main Reference Generation
Note:
7.31.3 5V Standby Reference Generation
SMSC LPC47M172
REF5V is used to help power-up various system components’ 5V tolerant buffers. This signal is used to
guarantee there are no power sequencing requirements at each particular system component.
REF5V is powered by VCC when VCC5V < VCC.
Upon motherboard power-up, REF5V is an analog output signal that tracks either VCC or VCC5V (through
an external pull-up resistor), whichever is greater in amplitude. REF5V becomes a high impedance input
while tracking the VCC power supply.
The maximum voltage drop across the diode is 350mV.
REF5V_STBY is generated in the same manner as REF5V, but in reference to V_5P0_STBY and VTR
instead. REF5V_STBY serves the same purpose as REF5V, but tracks different power supplies.
REF5V_STBY is an analog output signal that tracks either VTR or V_5P0_STBY, whichever is greater in
amplitude.
Upon motherboard power-up, REF5V_STBY is an analog output signal that tracks either VTR or
V_5P0_STBY (through an external pull-up resistor), whichever is greater in amplitude. REF5V_STBY
becomes a high impedance input while tracking the V_5P0_STBY power supply.
REF5V_STBY is powered by VTR when VTR > V_5P0_STBY.
VCC (3.3V)
V_5P0_STBY < VTR
V_5P0_STBY > VTR
STANDBY SUPPLY
MAIN SUPPLY
VCC5V < VCC
VCC5V > VCC
Figure 7.8 - REF5V Circuit
DATASHEET
Table 7.26 - REF5V_STBY
Table 7.25 - REF5V
Page 135
SMSC I/O
Protection
Backdrive
REF5V_STBY
REF5V
VCC
VTR
Hi-Z
Hi-Z
Advanced I/O Controller with Motherboard GLUE Logic
SMSC/Non-SMSC Register Sets (Rev. 02-27-04)
REF5V
VCC5V
1k
Datasheet