5
DESCRIPTION OF POWER SOURCES AND CLOCK INPUT/OUTPUTS
5.1 3.3 Volt Operation / 5 Volt Tolerance
The LPC47S45x is a 3.3 Volt part. It is intended solely for 3.3V applications. Non-LPC bus pins are 5V tolerant; that
is, the input voltage is 5.5V max, and the I/O buffer output pads are backdrive protected.
The LPC interface pins are 3.3 V only. These signals meet PCI DC specifications for 3.3V signaling. These pins are:
LAD[3:0]
LFRAME#
LDRQ#
LPCPD#
The input voltage for all other pins is 5.5V max. These pins include all non-LPC Bus pins and the following LPC Bus
pins:
PCI_RESET#
PCI_CLK
SER_IRQ
IO_PME#
5.2 Power Functionality
The LPC47S45x has three power planes: VCC, VTR, and Vbat.
5.2.1 VCC POWER
The LPC47S45x is a 3.3 Volt part. The VCC supply is 3.3 Volts (nominal). See the Operational Description Section
and the Maximum Current Values subsection.
5.2.2 VTR SUPPORT
The LPC47S45x requires a trickle supply (VTR) to provide sleep current for the programmable wake-up events in the
PME interface when VCC is removed. The VTR supply is 3.3 Volts (nominal). See the Operational Description
Section. The maximum VTR current that is required depends on the functions that are used in the part. See Trickle
Power Functionality subsection and the Maximum Current Values subsection. If the LPC47S45x is not intended to
provide wake-up capabilities on standby current, VTR can be connected to VCC. The VTR pin generates a VTR Power-
on-Reset signal to initialize these components.
Note: If VTR is to be used for programmable wake-up events when VCC is removed, VTR must be at its full minimum
potential at least 10 μs before Vcc begins a power-on cycle. When VTR and Vcc are fully powered, the potential
difference between the two supplies must not exceed 500mV.
5.2.3 VBAT INPUT
Vbat is a battery generated power supply that is needed to support the real-time clock and CMOS RAM. The real-
time clock keeps updating the time and date in the background even when the system is powered down. The CMOS
RAM holds the configurations data, which is read by the ROM BIOS at boot-up. The ROM BIOS reads the real-time
clock and the CMOS configuration registers to determine the current configuration as well as time and date.
The Vbat supply is 3.0 Volts (nominal). See the Operational Description Section and the Maximum Current Values
subsection.
The following pins are powered by Vbat:
XOSEL
XTAL1
XTAL2
The following Runtime Registers are powered by Vbat:
VCC Power On Elapsed Time Counter registers at offset 0x6D to 0x70.
SMSC DS – LPC47S45x
Page 19 of 259
Rev. 07/09/2001
DATASHEET
SMSC [ SMSC CORPORATION ]
