ADP3522ACP-1.8 datasheet(17/20 Pages) AD

17 / 20 page

REV. 0

ADP3522

–17–

1.75

1.25

2.00

1.50

0.75

0.25

1.00

0.50

100

120

TIME – Minutes

CHARGE CHARACTERISTIC

Figure 7. Kanebo PAS621 Charge Characteristic

1.75

1.25

2.00

1.50

0.75

0.25

1.00

0.50

100

120

TIME – Minutes

CHARGER CHARACTERISTIC

Figure 8. Panasonic EECEM0E204A Charge Characteristic

1.9

510

1.7

2.0

TIME – Hours

1.8

1.5

1.3

1.6

1.4

0.9

1.2

1.0

1.1

CHARGE CHARACTERISTIC

Figure 9. Maxell TC614 Charge Characteristic

1.9

510

1.7

2.0

TIME – Hours

1.8

1.5

1.3

1.6

1.4

0.9

1.2

1.0

1.1

CHARGER CHARACTERISTIC

Figure 10. Seiko TS621 Charge Characteristic

RTC Backup Coin Cell Selection

The choice of the backup cell is based upon size, cost, and

capacity. It must be able to support the RTC module’s current

requirement and voltage range, as well as handle the charge

current supplied by the ADP3522 (see TPC 2). Check with the

coin cell vendor if the ADP3522’s charge current profile is

acceptable.

Some suitable coin cells are the electric double layer capacitors

available from Kanebo (PAS621), Seiko (XC621), or Panasonic

(EECEM0E204A). They have a small physical size (6.8 mm

diameter) and a nominal capacity of 0.2 F to 0.3 F, giving hours

of backup time. Rechargeable lithium coin cells, such as the

TC614 from Maxell or the TS621 from Seiko, are also small in

size but have higher capacity than the double layer capacitors,

resulting in longer backup times. Typical charge curves for each

cell type are shown in Figures 7 through 10. Note that the

rechargeable lithium type coin cells generally come precharged

from the vendor.

RESET Capacitor Selection

RESET is held low at power up. An internal power-good signal

starts the reset delay when the core LDO is up. The delay is set

by an external capacitor on RESCAP:

RESET

RESCAP

=×

(4)

A 100 nF capacitor will produce a 120 ms reset delay. The

current capability of

RESET is minimal (a few hundred nA)

when VCORE is off to minimize power consumption. When

VCORE is on,

RESET is capable of driving 500

µA.

Setting the Charge Current

The ADP3522 is capable of charging both lithium ion and

NiMH batteries. For NiMH batteries, the charge current is

limited by the adapter. For lithium ion batteries, the charge

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