ICS1722 datasheet(11/24 Pages) GALAXY

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ICS1722

Master Reset: MRN Pin

The MRN pin is provided to re-program the controller for a new

mode or charging sequence. This pin has an internal pull-up of

about 75k

Ω. A logic low on the MRN pin must be present for more

than 700ms for a reset to occur. As long as the pin is low, the

controller is held in a reset condition. A master reset is required to

clear the charging system test, reset the ten hour timer, change

charge rates or auxiliary modes. Upon power-up, the controller

automatically resets itself.

Clock Input: RC Pin

The RC pin is used to set the frequency of the internal clock when

an external 1 MHz clock is not available. An external resistor must

be connected between this pin and VDD. An external capacitor

must be connected between this pin and ground. The frequency of

the internal clock will be about 1 MHz with a 16k

Ω resistor and a

100pF capacitor. All time durations noted in this document are

based on a 1 MHz clock. Operating the clock at a lower frequency

will proportionally change all time

durations. Operating the clock at a frequency significantly lower

than 1 MHz, without adjusting the charge current accordingly, will

lessen the effectiveness of the fast charge timer and lower the

accuracy of the controller. Operating the clock at a frequency

greater than 1 MHz will also change all time durations and, without

adjusting the charge current accordingly, may cause termination to

occur due to the fast charge timer expiring rather than by the

battery reaching full charge.

The clock may be driven by a 1 MHz external 0 to 5V pulse

provided the duty cycle is between 10% and 60%. The clock input

impedance is about 1k

Ω.

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 7. 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)

Figure 7: Resistor divider network

at the VIN pin

Open Circuit Voltage Reference: OPREF Pin

The OPREF pin has an internal 75k

Ω pull-up resistor to V

OPREF requires an external pull-down resistor 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 ICS1722 assumes

the battery has been removed and the ICS1722 enters the polling

detect mode.

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

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

and above the maximum normalized battery voltage. The OPREF

pin voltage must not exceed 2.3V or it will prevent the start of fast

charge. If the voltage on OPREF exceeds 4V, the controller will

shutdown and must be reset.

As an example, suppose that a current source has an open circuit

voltage of 12V as shown in Figure 8. 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 pull-

down resistor. Refer to the VIN and OPREF 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 pull-down resistor is 43k

Ω for R3. If R3 is 43kΩ, the

voltage at OPREF is 1.82V since the internal pull-up at the OPREF

pin is 75k

Ω.

VIN pin

# of cells

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