pc87591l National Semiconductor Corporation, pc87591l Datasheet - Page 360

• Manufacturer Part Number: pc87591l
• Description: Lpc Mobile Embedded Controllers
• Manufacturer: National Semiconductor Corporation

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Host-Controlled Modules and Host Interface
6.2.9
The PC87591x is supplied from four supply voltages, as shown in Figure 116 (see Section 3.1 on page 62 for more detailed
description):
A standby voltage (V
Figure 117 shows a typical battery configuration. No external diode is required to meet the UL standard, because of the in-
ternal switch and internal serial resistor R
RTC power is supplied from either V
parator delivers the control signals to a pair of switches. When V
voltage (V
or disconnection of the main battery. Figure 117 illustrates the mechanism whereby V
To assure that the module uses power from V
minimum (V
line) and V
The actual voltage point where the PC87591x switches from V
age but high enough to guarantee the correct functionality of the oscillator and the CMOS RAM.
The Valid RAM and Timer bit (VRT) in CRD register indicates the state of non-interrupted power supplied to the
PC87591x RTC module. VRT is cleared once V
host code should read this bit as part of the startup routine, before using the timer or the CMOS-RAM contents. In case
a value of 0 is read, the RAM and timer must be initialized before use. The VRT bit is set once read.
System power supply voltage, V
System analog power supply voltage, AV
System standby power supply voltage, V
Backup voltage, from low-capacity Lithium battery
Power Supply
BAT
BAT
CC2PP
) maintains the correct time and saves the CMOS memory when the V
(thin red line) and vice-versa for generating V
), as detailed in Section 7 on page 372. Figure 118 illustrates the switching between V
CC
) from the external AC/DC power supply powers the RTC under normal conditions.
1. Place a 0.1 F capacitor on each V
2. Place a 10-47 F capacitor on the common power
V
ACPI Controller
PP
pin as close as possible to the pin, and also on V
supply net as close as possible to the device.
DD
CC
RTC
Figure 117. Typical Battery Configuration
Figure 116. Power Supply Connections
or V
UL
.
BAT
CC
V
V
CC
PC0
V
DD Sense
BAT
CC
CC
voltage source, according to the sources’ levels. An internal voltage com-
PP
and not from V
power is lost, i.e., when V
RTC
V
V
BAT
V
CC
REF
360
PP
BAT
CC
(Continued)
ONCTL
(thin blue line).
V
AV
V
V
V
BAT
is active, the RTC power is drawn from it. Battery backup
to V
V
R
BAT
DD
CC
BAT
CC
UL
CC
, the V
CC
External AC Power
CC
power supply
is lower than the minimum workable battery volt-
0.1 F
0.1
ONCTL
V
V
CC
Supply
DD
Backup
Battery
Power
CF
CC
CF
CC
F
voltage should be maintained above its
and V
CC
BAT
voltage is absent due to power failure
CC
BT1
V
.
CC
BAT
or V
are both below V
BAT
is selected.
CC
LOWBAT.
(thick green
Revision 1.07
The