ISL9205, ISL9205A, ISL9205B, ISL9205C, ISL9205D

FN9252 Rev 3.00

Page 12 of 17

September 30, 2016

Theory of Operation

The ISL9205 family is an integrated charger for single-cell Li-ion

or Li-polymer batteries. The ISL9205 family is capable of

operating in two operation modes, linear charge mode and pulse

charge mode. The ISL9205 family functions as a traditional

linear charger when powered with a voltage source adapter.

When powered with a current-limited adapter, the charger

functions as a pulse charger by fully turning on the pass element,

thereby reducing the power dissipation.

Constant Current Phase

The ISL9205 family starts the charge at a Constant Current (CC)

phase. The charge current is regulated to fast charge the battery

before the final voltage has been reached. The charge current is

programmable with the IREF pin and has two operation modes:

trickle mode and Constant Current mode, depending on the

battery voltage. When the battery voltage is lower than 2.8V, the

charger operates in trickle mode where the charge current is set

at 10% of the Constant Current mode current. The trickle mode is

for preconditioning a deeply discharged battery. Once the battery

voltage is above the typical 2.8V threshold, the Constant Current

mode starts. The constant current is programmable between

50mA to 1A.

Constant Voltage Phase

When the battery reaches the final voltage, the ISL9205

switches the operation to a Constant Voltage (CV) phase. The

output voltage is regulated at the final voltage value. During the

Constant Voltage phase, the charge current reduces gradually as

the cell voltage rises.

End-of-Charge and Recharge

As the charge current reaches the End-of-Charge (EOC) current

threshold during the Constant Voltage phase, the STATUS pin

open-drain FET is turned off to indicate an EOC condition. The

EOC current is programmable for the ISL9205 by connecting a

resistor from the IMIN pin to GND. For others, the EOC current is

fixed at 10% of the programmed constant charge current. When

the STATUS pin indicates the EOC condition, the charger will

continue to charge until the EN pin is pulled to logic LOW or the

input power has been removed. After EOC is reached, recharge

will occur when the battery voltage falls to 150mV below the

constant voltage value. The STATUS open-drain FET is turned on

when a recharge condition is met. An internal delay is

implemented at the STATUS pin for both EOC and recharge

conditions to prevent nuisance trips due to noise and fast load

current transitions. The delay time is approximately one clock

cycle (varies between 0.5 and 1.5 clock) of the internal oscillator,

which is programmed by the timer capacitor. The typical charge

waveforms in Figure 16 show the complete cycle operation.

Temperature Monitoring and Thermal

Foldback

In the event the die temperature reaches the thermal foldback

threshold (+110°C typical), the charge current is reduced

accordingly to prevent further temperature rise. In the ISL9205

and ISL9205D versions, there is an external temperature

monitoring function. A Negative Temperature Coefficient (NTC)

thermistor can be connected between the TEMP pin and GND to

monitor the battery temperature or ambient temperature. The

hysteresis comparators internal to the ISL9205 family provide a

valid temperature window centered at the voltage of the TEMP

pin, which is programmed by the NTC and the pull-up resistor

connected to the pin. When the measured temperature is outside

this window, the charger is paused (both the charger and the

timer are stopped) and a fault indication is issued. If the

thermistor is attached to the battery, the TEMP function can be

used to discover a battery removal condition when the TEMP pin

voltage is much higher than the reference threshold.

POR

The Power-on Reset (POR) function monitors the supply voltage.

The POR has a rising edge threshold of 3.6V typical and 2.5V

typical for falling edge. The charger is expected to operate when

the input voltage is above the POR threshold. After POR, the

charger will continue to operate for supply voltage down to 2.5V

typical. It is also required that the supply voltage be higher than

the VBAT pin voltage by a typical 80mV for the charger to

function.

FIGURE 16. TYPICAL CHARGE CYCLE WITH TIMEOUT

4.2V

TIME

2.8V

CHG

CHARGE

CURRENT

CHARGE

VOLTAGE

STATUS

INDICATION

TRICKLE

CC

CV