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SM6780AS

NIPPON PRECISION CIRCUITS—4

FUNCTIONAL DESCRIPTION

Charger Operation

The SM6780AS battery charger operation starts

when the power is applied or when standby mode is

released. The charging operation is determined by

the BATT and TEMP pin states, and the timer mode

selected.

After charging starts, the battery voltage and temper-

ature are monitored to check that they are within

quick charging rated ranges. If within rated range,

quick charge mode is selected. If outside rated range,

pulse trickle charge mode is selected.

Quick charge uses either negative delta voltage

detection (

−∆V), temperature detection (∆T/∆t), or

charging time cutoff to terminate the charging pro-

cess. The charging mode changes to supplemental

charge mode when quick charge mode is completed.

Supplemental mode terminates when the charging

time ﬁnishes or battery is full, and the charging mode

changes to pulse trickle mode.

Charging Rate

The charging rate is determined by the external

charger current source. If the quick charge mode

charging rate is considered as unity, then the supple-

mental charging rate is 1/16, and the pulse trickle

charging rate is 1/256. The charging rate for supple-

mental and pulse trickle modes are shown in ﬁgure 1.

The CHGN output is high impedance when the

charging current is ﬂowing, and LOW when the cur-

rent stops.

Charging Status Indicator LED Control (LEDN)

The SM6780AS LEDN output can be used to drive a

charging status indicator LED.

The LED timing when power is applied or standby

mode is released is shown in ﬁgure 2.

In quick charge mode, the LEDN output is LOW and

the LED turns ON. If the battery temperature or bat-

tery voltage exceeds the charging rated ranges, the

LEDN output pulses at a frequency of 1Hz to indi-

cate battery out-of-range condition. In supplemental

and pulse trickle modes, the LEDN output is high

impedance and the LED turns OFF.

Figure 1. CHGN output (external charger control)

Hi-Z

Low

286

µs

73.1ms

4576

µs

Quick charge

mode

Supplemental

charge mode

Pulse trickle mode

Start

(power ON or battery insertion)

286

µs

Figure 2. LEDN output timing

Hi-Z

Low

LED OFF

Power ON or Standby mode cancel

LED ON

Approximately

1.5 s

Approximately

3.5 s

Depends on charge mode

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