ISL9205, ISL9205A, ISL9205B, ISL9205C, ISL9205D

FN9252 Rev 4.00

Page 11 of 17

Dec 20, 2018

Theory of Operation

The ISL9205 family are integrated chargers for single-cell Li-ion

or Li-polymer batteries. They are capable of operating in two

operation modes, Linear Charge mode and Pulse Charge mode.

They function as traditional linear chargers when powered with a

voltage source adapter. When powered with a current-limited

adapter, the chargers function as pulse chargers 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. Trickle mode is for

preconditioning a deeply discharged battery. When 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 ISL9205A, ISL9205B,

ISL9205C, and ISL9205D, the EOC current is fixed at 10% of the

programmed constant charge current. When the STATUS pin

indicates the EOC condition, the charger continues to charge until

the EN pin is pulled to logic LOW or the input power has been

removed. After EOC is reached, recharge occurs 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 the falling edge. The charger is expected to operate

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

the charger continues 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

IREF

IMIN

4.2V

TIME

2.8V

CHG

CHARGE

CURRENT

CHARGE

VOLTAGE

STATUS

INDICATION

VREC

10% IREF

TRICKLE

CC

CV