ICS1702 datasheet(16/28 Pages) ETC

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ICS1702

Figure 13: Resistor divider network

at the VIN pin

Open Circuit Voltage Reference: OPREF Pin

The OPREF pin requires an external resistor divider to establish

the open circuit (no battery) voltage reference. The purpose of this

voltage reference is to detect the removal of the battery from the

charging system. The voltage at this pin is compared to the voltage

at the VIN pin when the current source is turned on. If the voltage

at VIN is greater than the voltage at OPREF, the ICS1702 assumes

the battery has been removed and the ICS1702 enters the polling

detect mode.

For proper operation, the voltage at OPREF must be set between

the (divided down) open circuit voltage produced by the current

source and the maximum normalized battery voltage. An example

is shown in Figure 14.

Suppose that a current source has an open circuit voltage of 12V.

The maximum expected battery voltage of a six-cell pack is

determined to be 9.6V. The voltage at OPREF should be set at a

point between 1.6V (9.6V/6 cells=1.6V) and 2V (12V/6=2V). This

is accomplished with a resistor divider network. In this example,

R4 and R3 are referred to VDD. Refer to the VIN and OPREF

divider resistor tables in the Applications Information section.

From the VIN table, the divider resistors are 10k

Ω and 2kΩ for R1

and R2. From the OPREF table, the divider resistors are 2.2k

Ω and

1.3k

Ω for R3 and R4. If R3 is 2.2kΩ and R4 is 1.3kΩ, the voltage

at OPREF is 1.86V.

•Using no temperature sensor:

If a temperature sensor is not used, the THERM pin must be

grounded.

Termination Selection: DTSEL Pin

The ICS1702 has the capability of either temperature slope

termination,

voltage

slope

termination

both

methods

simultaneously. The DTSEL pin has an internal 75k

Ω pull-down

resistor that enables voltage slope termination as the primary

method and is the default condition. Tying the pin high enables

both temperature slope and voltage slope termination methods.

Temperature slope termination as the primary method is enabled by

tying the DTSEL pin to the CMN output (pin 5). CMN must have

an external 15k

Ω or lower value pull-up resistor to V

for proper

activation of temperature slope termination. The ICS1702 must be

reset if a new termination method is desired. Table 8 summarizes

the DTSEL pin settings. NOTE: Maximum temperature and fast

charge timer termination methods are always enabled when using

temperature slope termination. Refer to the sections on Fast

Charge

Timer

Termination

and

Maximum

Temperature

Termination for more information.

Table 8: Termination Select List

Voltage Input: VIN Pin

The battery voltage must be normalized by an external resistor

divider network to one cell. The electrochemical potential of one

cell is about 1.2V. For example, if the battery consists of six cells

in series, the voltage at the VIN pin must be equal to the total

battery voltage divided by six. This can be accomplished with two

resistors, as shown in Figure 13. To determine the correct resistor

values, count the number of cells to be charged in series. Then

choose either R1 or R2 and solve for the other resistor using:

R1 = R2 * (# of cells -1) or R2 =

(# of cells -1)

VIN pin

# of cells

Tie DTSEL

Pin to ...

Result

Low

(No Connect)

Voltage slope termination only

High

Voltage slope and temperature slope

termination

CMN

Temperature slope termination only

(CMN with external pull-up to VDD)

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