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6 power supply, Figure 5-8, Power supply connections – AMD Geode SC1201 User Manual

Page 108: Figure 5-9, Typical battery configuration, Figure 5-10, Figure 5-11, Typical battery current: normal operation mode

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108

AMD Geode™ SC1200/SC1201 Processor Data Book

SuperI/O Module

32579B

5.5.2.6

Power Supply

The device is supplied from two supply voltages, as shown
in Figure 5-8:

System standby power supply voltage, V

SB

Backup voltage, from low capacity Lithium battery

A standby voltage, V

SB

, from the external AC/DC power

supply powers the RTC under normal conditions.

Figure 5-9 represents a typical battery configuration. No
external diode is required to meet the UL standard, due to
the internal switch and internal serial resistor R

UL

.

Figure 5-8. Power Supply Connections

Figure 5-9. Typical Battery Configuration

The RTC is supplied from one of two power supplies, V

SB

or V

BAT

, according to their levels. An internal voltage com-

parator delivers the control signals to a pair of switches.
Battery backup voltage V

BAT

maintains the correct time and

saves the CMOS memory when the V

SB

voltage is absent,

due to power failure or disconnection of the external AC/DC
input power supply or V

SB

main battery.

To assure that the module uses power from V

SB

and not

from V

BAT

, the V

SB

voltage should be maintained above its

minimum, as detailed in Section 9.0 "Electrical Specifica-
tions" on page 365.

The actual voltage point where the module switches from
V

BAT

to V

SB

is lower than the minimum workable battery

voltage, but high enough to guarantee the correct function-
ality of the oscillator and the CMOS RAM.

Figure 5-10 shows typical battery current consumption dur-
ing battery-backed operation, and Figure 5-11 during nor-
mal operation.

Figure 5-10. Typical Battery Current: Battery

Backed Power Mode @ T

C

= 25°C

Figure 5-11. Typical Battery Current: Normal

Operation Mode

RTC

Power

Backup

V

DIGITAL

V

SB

V

DIGITAL

V

SB

V

BAT

Battery

External AC Power

Supply

V

DIGITAL

Sense

V

SB

V

BAT

V

SB

PC0

V

BAT

ONCTL#

ONCTL#

ACPI Controller

V

BAT

0.1

μF

V

SB

V

SB

C

F

C

F

BT

1

0.1

μF

V

PP

R

UL

V

REF

RTC

Note:

Place a 0.1

μF capacitor on each V

SB

, V

SBL

power supply pin as close as possible to the
pin, and also on V

BAT

.

V

SBL

C

F

0.1

μF

V

SBL

I

BAT

(

μA)

10.0

7.5

5.0

2.5

2.4 3.0 3.6

V

BAT

(V)

I

BAT

(

μA)

0.75

0.50

0.25

3.0 3.3 3.6

V

SB

Note: Battery voltage in this test is 3.0V.

(V)

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