12

ICS1708

Timing Diagram

Figure A:

Applications Information

To ensure proper operation of the ICS1708, external components must be properly selected. The external current source used must meet

several important criteria to ensure adequate performance of the charging system. The charging current source amplitude should be fairly

constant

VIN and OPREF Divider Resistors

Figure 9 shows a typical application using the ICS1708. R1 through R3 must be selected properly to ensure that battery detection and

voltage termination methods operate properly. R1 and R2 are selected to scale the battery voltage down to the voltage of one cell. The

following table shows some typical values.

Cells

R1

R2

1

20k

*

2

20k

20k*

3

39k

20k

4

62k

20k

5

82k

20k

6

100k

20k

7

120k

20k

8

150k

20k

9

160k

20k

10

180k

20k

11

200k

20k

12

220k

20k

13 & Above

R1=R2 x (# cells - 1)

* Use 5.1V Zener as required depending on input voltage

If the current source is a switch mode type, normal ripple current does not effect the ICS1708. However, the effects of line frequency ripple

may interfere with proper performance. R3, per Figure 9, can be used to set the open circuit (no battery) reference voltage on the OPREF

pin. The function of this pin is discussed in the Open Circuit Reference section.

R3

1.68 V

43k

1.78 V

47k

1.88 V

51k

1.99 V

56k

2.11 V

62k

See Figure 8 for an alternate resistor divider approach at the OPREF pin for tight tolerance applications.

CYCLE

FCHG

REST

CHG

pin 1

DATA

ACQUISITION

+5V