MAX1898 データシートの表示（PDF） - Maxim Integrated

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MAX1898

Linear Charger for Single-Cell Li+ Battery

Maxim Integrated 

Linear Charger for Single-Cell Li+ Battery

power is present at IN. If there is no (or insufficient)

voltage at IN, EN/OK will remain low and the charger

will remain off.

Battery Drain Current

The MAX1898 uses advanced CMOS circuitry to com-

pletely monitor battery state, while drawing minimal current

from the cell itself. When the input voltage is less than the

battery, battery drain is typically 3µA. When input power is

present and charging is complete (the charge timer

expires), battery drain is then typically 40µA. This current

may be reduced to 4µA by disabling the restart feature.

Applications Information

The MAX1898 basic application circuit is shown in

Figure 4.

5V TO 12V

100nF

CHARGE LED

INDICATOR

INPUT POWER

OK OUTPUT OR

ENABLE INPUT

CS 10

1 IN

DRV 9

BATT 7

MAX1898

2

CHG

CT 5

3

EN/OK

6

RSTRT GND

8

4

ISET

10µF

Li+ CELL

CCT, 100nF CAPACITOR

SETS CHARGE TIME

TO 3hr

OUTPUT VOLTAGE

PROPORTIONAL

TO CHARGE CURRENT

RSET SETS

CHARGE

CURRENT

Figure 4. Basic Application Circuit

An LED can be added as a charge-state indicator. A

10µF bypass capacitor must be added to the BATT pin.

A Schottky diode should be added between the exter-

nal transistor drain/collector and BATT, to avoid battery

discharge in the event of an input source short circuit.

Figure 5 shows a charger circuit using an external PNP

pass transistor.

Selecting Maximum Charge Time

The maximum charge time can be set with an external

capacitor connected from CT to GND. Select the timing

capacitor using:

5V TO 12V

220nF

CHARGE LED

INDICATOR

INPUT POWER

OK OUTPUT OR

ENABLE INPUT

CS 10

1 IN

DRV 9

BATT 7

MAX1898

2

CHG

5

CT

3

EN/OK

6

RSTRT GND

8

4

ISET

10µF

Li+ CELL

CCT, 100nF CAPACITOR

SETS CHARGE TIME

TO 3hr

OUTPUT VOLTAGE

PROPORTIONAL

TO CHARGE CURRENT

RSET SETS

CHARGE

CURRENT

Figure 5. Application Circuit with PNP Pass Transistor

CCT[nF] = 34.33 × tCHG[hours]

where:

tCHG = nominal charge time limit in hours.

The maximum charge timer is intended as a safety timer.

It is normally not intended to be part of the charge-con-

trol loop. When charging a Li+ cell at a 1C rate, normal

charge time is approximately 1.5 hours, but this may

have wide variations that depend on temperature and

cell type. In most cases, 3 hours is recommended for the

maximum charge time limit when fast-charging at 1C so

that normal-charging is never interrupted by the charge

timer. Consult the battery manufacturer for details on rec-

ommended timer settings.

The charge safety timer may also be completely dis-

abled by connecting CT to ground. Note: If the charge

timer is disabled, both the restart function and prequali-

fication fault indication are also disabled. Only the indi-

cation (blinking LED) is disabled, the prequalification

function itself is not modified.

Controlling Automatic Restart

The MAX1898 features automatic restart that resumes

charging when the cell voltage drops to a predetermined

level. In most timed chargers, once charging times out,

subsequent loading of the battery can discharge the bat-

tery and charging will not resume unless the charger is

restarted by an outside signal. By automatically resuming

charging when the battery voltage drops, the MAX1898

ensures that the cell does not remain partially charged

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