8

ICS1708

As an example, suppose that a current source has an open circuit voltage of 12V as shown in Figure 8.

Figure 8: Open Circuit Reference Example

The maximum battery voltage of a nearly full six-cell pack with current applied is determined to be 9.6V. The voltage at OPREF should

then be set at a point between 1.6V (9.6V/6 cells=1.6V) and 2V (12V/6=2V). This can be accomplished with a pull-down resistor. Refer to

the VIN and OPREF resistor tables in the Applications Information section. From the VIN table, the divider resistors are 100k

20k

1.78V since the internal pull-up at the OPREF pin is 85k

tolerance applications.

Power: VDD pin 8

The power supply for the device must be connected to the VDD pin. The voltage is +5 VDC nominal, series regulated for proper noise

rejection. A 100mA or higher current rating supplies the controllers maximum of 11mA average demand that includes brief 50mA peaks.

Peripheral circuits current requirements are added to these requirements. See Pin Descriptions for additional information.

Grounding: VSS pin 6

This pin is connected directly to a solid (low impedance) ground that connects at or close to battery minus. See the section Pin Descriptions

and Applications Information (PC Board Design Considerations) for additional information.

Charge Rate Selection

The voltage set on CMN pin 3 prior to the start of fast charge sets one of three fast charge rates shown in Table 2.

Table 2: Charge Rate List

Selected Charge Rate

Topping Charge Pulse

Rate

Maintenance Charge

Pulse Rate

Fast Charge Timer

Duration (after power-

up or battery insertion)

4C (15 min)

one every 41 sec

one every 161 sec

21 min

1C (60 min)

one every 11 sec

one every 41 sec

75 min

C/2.5 (150 min)

one every 5 sec

one every 17 sec

212 min

See the section on Controller Operation for additional information on the topping charge and maintenance charge. See the section on Charge Termination

Methods for additional information on the charge timer.

+ 5 V

R4 = 1.3k, 1%

R3 = 2.21k, 1%

R1 = 100k

R2 = 20k

6 cells

+

-

VIN =

OPREF = 1.89V

current source on (no battery)

(open circuit voltage = 12V)

{

1.60V (battery present)

2.00V (no battery)

(9.6 V)

Alternate resistor divider at the OPREF

pin for tight tolerance applications

Resistor di vider at the VIN

pin