SCH3112I-NE SMSC [SMSC Corporation], SCH3112I-NE Datasheet - Page 199

• Manufacturer Part Number: SCH3112I-NE
• Description: LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
• Manufacturer: SMSC [SMSC Corporation]

LPC IO with 8042 KBC, Reset Generation, HWM and Multiple Serial Ports
Datasheet
Chapter 21 Low Battery Detection Logic
SMSC SCH311X
21.1
21.2
21.2.1
Battery
The low battery detection logic monitors the battery voltage to detect if this voltage drops below 2.2V
and/or 1.2V. If the device is powered by Vbat only and the battery voltage is below approximately
1.2V, a VBAT POR will occur upon a VTR POR. If the device detects the battery voltage is below
approximately 2.2V while it is powered by Vbat only or VTR (VCC=0V) the LOW_BAT PME and SMI
Status bits will be set upon a VCC POR. When the external diode voltage drop is taken into account,
these numbers become 1.5V and 2.5V, respectively.
The LOW_BAT PME event is indicated and enabled via the PME_STS1 and PME_STS1 registers.
See PME_STS1 for a description of these registers.
The LOW_BAT SMI event is indicated and enabled via the
the
The following figure illustrates external battery circuit.
Note that the battery voltage of 2.2V nominal is at the VBAT pin of the device, not at the source.
When VBAT drops below approximately 1.2V while both VTR and VCC are off, a VBAT POR will occur
upon a VTR POR.
The LOW_BAT PME and SMI Status bits is set to ‘1’ upon a VBAT POR. Since the PME enable bit
is not battery backed up and is cleared on VTR POR, the VBAT POR event is not a wakeup event.
When VCC returns, if the PME or SMI enable bit (and other associated enable bits) are set, then the
corresponding event will be generated.
Under Battery Power
If the battery voltage drops below approximately 2.2V under battery power (VTR and VCC off) then
the LOW_BAT PME and SMI Status bits will be set upon a VCC POR. This is due to the fact that the
LOW_BAT event signal is only active upon a VCC POR, and therefore the low battery event is not a
wakeup event. When VCC returns, if the PME or SMI enable bit (and other associated enable bits)
are set, then a corresponding event will be generated.
VBAT POR
Low Battery
Chapter 26, "Runtime Register," on page 293
Figure 21.1 External Battery Circuit
DATASHEET
183
section for a description of these registers.
SMI_STS1
VBAT
SCH311X
ICH
and
V
LPC47M292
BATLOW
SMI_EN1
~2.2V
Rev 0.2 (09-28-04)
registers. See