ICS1722M datasheet(15/24 Pages) GALAXY

15 / 24 page

ICS1722

Applications Information

To ensure proper operation of the ICS1722, external components

must be properly selected. The external current source used must

meet several important criteria to ensure optimal performance of

the charging system. The charging current should be constant when

using voltage slope termination.

VIN and OPREF Divider Resistors

Figure 9 shows a typical application using the ICS1722. R1

through R3 must be carefully selected 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.

Additional information is available in the Voltage Input section.

Cells

Short

Open

2.0k

1.0k

3.0k

1.0k

12k

3.0k

10k

2.0k

12k

2.0k

9.1k

1.3k

The current source should prevent ripple voltage from appearing on

the battery. The effects of ripple on the battery voltage may

interfere with proper operation.

R3 is 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.

OPREF

1.82 V

43k

1.93 V

47k

2.02 V

51k

2.14 V

56k

With the batteries removed, the current source must be capable of

raising the voltage at the VIN pin above the voltage at the OPREF

pin to ensure proper polling. With the batteries in-stalled, the

current source overshoot characteristics when turned on and off

must not cause the voltage at the VIN pin to exceed the voltage at

the OPREF pin. If the voltage at OPREF exceeds the voltage at

VIN when a charge pulse is applied or removed, the polling feature

will be activated.

PC Board Design Considerations

It is very important that care be taken to minimize noise coupling

and ground bounce. In addition, wires and connectors can add

significant resistance and inductance to the charge and discharge

circuits.

When designing the printed circuit board, make sure ground and

power traces are wide and bypass capacitors are used right at the

controller. Use separate grounds for the signal, charge and

discharge circuits. Separate ground planes on the component side

of the PC board are recommended. Be sure to connect these

grounds together at the negative lead of the battery only. For the

discharge circuit, keep the physical separation between power and

return (ground) to a minimum to minimize field radiation effects.

This precaution is also applicable to the constant current source,

particularly if it is a switch mode type. Keep the ICS1722 and the

constant current source control circuits outside the power and

return loop described above. These precautions will prevent high

circulating currents and coupled noise from disturbing normal

operation.

Using the Voltage Slope Termination Method

In general, the voltage slope termination method works best

for equipment where the battery is fast charged with the equipment

off or the battery is removed from the equipment for fast charge.

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