CS1702 datasheet(20/28 Pages) ETC

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ICS1702

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 installed, 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 ICS1702 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.

Selecting the Appropriate 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. The

temperature slope and maximum temperature termination methods

are for equipment that must remain operative while the battery is

fast charged.

Applications Information

To ensure proper operation of the ICS1702, 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. The current may vary when using

temperature slope termination.

VIN and OPREF Divider Resistors

Figure 15 shows a typical application using the ICS1702. R1

through R4 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

If using voltage slope termination, 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

when using the voltage slope method.

R3 and R4 are 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

1.86 V

2.2k

1.3k

1.92 V

2.4k

1.5k

1.97 V

2.0k

1.3k

2.00 V

3.0k

2.0k

2.03 V

2.2k

1.5k

2.10 V

1.8k

1.3k

2.14 V

2.4k

1.8k

2.22 V

3.0k

2.4k

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