STLED325 datasheet(30/62 Pages) STMICROELECTRONICS

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Functional description

STLED325

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Doc ID 17576 Rev 1

spike is very low into the battery. The battery must be protected against such spikes. This is

not relevant for super-cap.

During the switching from VBAT to VCC, the I2C is active after a minimum of 5ms.

3.17.2

Battery low warning

The STLED325 automatically performs battery voltage monitoring upon power-up. If the

interrupt for this condition (ABE) is enabled, the RTC will generate an interrupt pulse if the

battery voltage is found to be less than a minimum of 2.5V. However, this condition is

unlikely to go away very quickly as time is needed for the battery to be replaced, and it is not

desirable to keep issuing an interrupt.

Therefore when this bit is set, this condition is checked once every week. If the condition is

still true, then interrupt is sent again.

The ABE bit is an enable bit for battery status check. If the ABE bit was set and the battery

low is generated during a power up sequence, this indicates that the battery is below

approximately 2.5 V and may not be able to maintain data integrity. At this point, a fresh

battery needs to be installed or the super-cap recharged.

This situation only occurs when a battery is used but not with a super-cap as the super-cap

re-charges when the supply is present.

3.17.3

Different power operation modes

The device is capable to support the different power modes as shown in the Table 8.

Table 8.

Different power operation modes

VCC

VBAT

Condition

Operation

Present

VCC > VBAT

Normal operation of

chip from VCC

Present

Absent (Float or 0V)

VCC > VBAT and

VCC > 3.5V

Normal operation of

chip from VCC until VCC

is 3.5V

Absent (Float or 0V)

Present

VBAT > 2.5V

Chip operations from

VBAT in a low power

mode of operation

VCC < 3.5V

VBAT > VCC

Chip operations from

VBAT in a low power

mode of operation

Absent (Float or 0V)

VCC < 3.5V and

VBAT < 2.5V

Chip does not function.

Completely shutdown.

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