9

ICS1708

The 1C (60 minute rate) is selected by using a 10K pull-up resistor from CMN pin 3 to VDD pin 8 (+5V REG.) as shown in

Figure 9A "Charging System Diagram". The 10K pull-up resistor is required even if an LED with a current limited pull-up to

VDD pin 8 (+5V reg.) is used. The C/2.5 (150 minute) rate is selected using the 330/1.3K resistor divider with a general

purpose LED as shown in Figure 9B. Based on the LED selection, this configuration should provide the 2.5V +/- 0.5V on

CMN pin 3 prior to the start of fast charge to activate the C/2.5 (150 minute) rate as shown in Figure 9B. Setting the 4C (15

minute) rate involves setting the voltage at CMN pin 3 below 0.5V prior to the start of fast charge as shown in Figure 9C. A

10K pull-up resistor, a 2K pull-down resistor and a 1N4148 or equivalent diode is used to keep CMN below 0.5V at power up

or upon battery removal. When CMN goes low to ground of its own accord, the base of a 2N3903 or equivalent NPN

transistor is pulled low via the 1N4148 diode allowing the LED indication for fast charge.

ICS1708

CONSTANT

CURRENT

SOURCE

PTC

or

TS

DC INPUT

.047uF

R3

R2

R1

100pF

15k

4.7uF

.047uF

+

IN

ON/OFF

OUT

1

2

3

4

5

6

7

8

CHG

MMN

CMN

VSS

VDD

VIN

OPREF

RC

+5V REG.

*10K

FIGURE 9A: Charging System Diagram for 1C (60 minute) Charge Rate

* SELECTS 1C

CHARGE RATE