SC2200 datasheet(118/433 Pages) NSC

118 / 433 page

www.national.com

118

Revision 3.0

SuperI/O Module (Continued)

4.5.2.7

System Power States

The system power state may be No Power, Power On,

Power Off or Power Failure. Table 4-18 indicates the power-

source combinations for each state. No other power-source

combinations are valid.

In addition, the power sources and distribution for the entire

system are illustrated in Figure 4-8 on page 117.

No Power

This state exists when no external or battery power is con-

nected to the device. This condition does not occur once a

backup battery has been connected, except in the case of

a malfunction.

Power On

This is the normal state when the system is active. This

state may be initiated by various events in addition to the

normal physical switching on of the system. In this state,

the system power supply is powered by external AC power

and produces VDIGITAL and VSB. The system and the part

are powered by VDIGITAL, with the exception of the RTC log-

ical device, which is powered by VSB.

Power Off (Suspended)

This is the normal state when the system has been

switched off and is not required to be active, but is still con-

nected to a live external AC input power source. This state

may be initiated directly or by software. The system is pow-

ered down. The RTC logical device remains active, pow-

ered by VSB.

Power Failure

This state occurs when the external power source to the

system stops supplying power, due to disconnection or

power failure on the external AC input power source. The

RTC continues to maintain timekeeping and RAM data

under battery power (VBAT), unless the oscillator stop bit

was set in the RTC. In this case, the oscillator stops func-

tioning if the system goes to battery power, and timekeep-

ing data becomes invalid.

System Bus Lockout

During power on or power off, spurious bus transactions

from the host may occur. To protect the RTC internal regis-

ters from corruption, all inputs are automatically locked out.

The lockout condition is asserted when VSB is lower than

VSBON.

Power-Up Detection

When system power is restored after a power failure or

power off state (VSB = 0), the lockout condition continues

for a delay of 62 msec (minimum) to 125 msec (maximum)

after the RTC switches from battery to system power.

The lockout condition is switched off immediately in the fol-

lowing situations:

• If the Divider Chain Control bits, DV[2:0], (CRA bits [6:4])

specify a normal operation mode (01x or 100), all input

signals are enabled immediately upon detection of

system voltage above VSBON.

• When battery voltage is below VBATDCT and HMR is 1,

all input signals are enabled immediately upon detection

of system voltage above VSBON. This also initializes

registers at offsets 00h through 0Dh.

• If bit 7 (VRT) of CRD is 0, all input signals are enabled

immediately upon detection of system voltage above

VSBON.

4.5.2.8

Oscillator Activity

The RTC oscillator is active if:

• VSB power supply is higher than VSBON, independent of

the battery voltage, VBAT

-or-

• VBAT power supply is higher than VBATMIN, regardless if

VSB is present or not.

The RTC oscillator is disabled if:

• During power-down (VBAT only), the battery voltage

drops below VBATMIN. When this occurs, the oscillator

may be disabled and its functionality cannot be guaran-

teed.

-or-

• Software wrote 00x to DV[2:0] bits of the CRA Register

and VSB is removed. This disables the oscillator and

decreases the power consumption from the battery

connected to VBAT. When disabling the oscillator, the

CMOS RAM is not affected as long as the battery is

present at a correct voltage level.

If the RTC oscillator becomes inactive, the following fea-

tures are dysfunctional/disabled:

• Timekeeping.

• Periodic interrupt.

• Alarm.

Table 4-18. System Power States

VDIGITAL

VSB

VBAT

Power State

−−−

No Power

−−

Power Failure

−

+ or -

Power Off

+ or-

PowerOn

SC2200 датащи(PDF) 118 Page - National Semiconductor (TI)

SC2200 датащи(HTML) 118 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL