SM6780AS datasheet(7/11 Pages) NPC

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SM6780AS

NIPPON PRECISION CIRCUITS—7

−∆V Invalid Time

Generally, the battery voltage becomes unstable just

after quick charging starts, so the

−∆V battery volt-

age detection is disabled for 5 minutes to avoid error

in battery voltage detection. However, the

∆T/∆t

temperature detection function continues to operate.

After the

−∆V detection is enabled, both detection

functions operate.

−∆V Detection (BATT)

After Ni-Cd and Ni-MH batteries are fully charged

in quick charge mode, the battery voltage begins to

drop after reaching a peak value. The SM6780AS

monitors the delta voltage (

−∆V) to help determine

when the battery is fully charged. When the voltage

has fallen a minimum of 8mV (typ), the battery is

fully charged and quick charge mode terminates.

Note that

−∆V detection is disabled for 5 minutes

when quick charge mode is ﬁrst started to avoid error

in battery voltage detection, as described in the pre-

vious section.

∆T/∆t Detection (TEMP)

When Ni-Cd and Ni-MH batteries are close to full

charge in quick charge mode, the temperature of the

battery begins to greatly increase. The SM6780AS

monitors the temperature change rate (

∆V/∆t) to help

determine when the battery is fully charged. When

the temperature voltage on TEMP decreases by a

minimum of 25mV (typ) within a 60-second interval,

the battery is considered to be fully charged and

quick charge mode terminates.

Note that the TEMP voltage decreases with increas-

ing temperature due to the negative temperature

coefﬁcient of the thermistor.

Figure 7. Battery voltage change

8mV

− ∆V detect

Vpeak

Quick charge time

Figure 8. Battery temperature change

Quick charge time

Cell temperature

Cell voltage

Figure 9. VTEMP change

Quick charge time

Cell voltage

60s

25mV

VTEMP

∆t

∆T

∆T/∆t detect

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