ISL9220, ISL9220A

11

FN6936.3

February 16, 2012

STAT1 and STAT2 are configured to indicate various charging

conditions as given in Table 1.

A fault status is triggered under one of these conditions:

2. Timeout occurs before the EOC current has been reached

To exit the fault mode, the input power has to be recycled, or the

EN pin is toggled to HI and back to LO.

Applications Information

Power-On Reset (POR)

The ISL9220, ISL9220A resets itself as the input voltage rises

above the POR rising threshold. The internal oscillator starts to

oscillate, the internal timer is reset, and the charger begins to

charge the battery. The STAT1/2 pins will indicate the operating

condition according to Table 1.

Trickle Charge

If the battery voltage is below the trickle charge threshold, the

ISL9220, ISL9220A delivers a small current to charge the battery

until the battery voltage reaches the fast charge threshold value.

There are two trickle charge thresholds. The first threshold,

the ISL9220, ISL9220A operates as a linear regulator, providing

the ISL9220, ISL9220A starts to operate as a switching charger.

The trickle charge current is programmable by RISET2.

Charge Cycle

A charge cycle consists of three charge modes: trickle mode,

constant current (CC) mode, and constant voltage (CV) mode. The

charge cycle always starts with the trickle mode until the battery

charger operates in CC mode after the battery voltage is above

charge voltage, the CV mode operation begins. Since the battery

terminal voltage is regulated at the constant output voltage in

the CV mode, the charge current begins to drop. After the charge

current drops below the end-of-charge level, which is

programmed by RISET2. The ISL9220, ISL9220A indicates the

end-of-charge (EOC) with STAT1 and STAT2 and terminates the

charge. The following events initiate a new charge cycle:

•POR

• A new battery being inserted (detected by RTH pin)

• Recovery from an battery over-temperature fault

•The EN pin is toggled from HI-to-LO

Recharge

After a charge cycle completes at a timeout event, charging is

then the charging restarts with the timer reset to zero.

Inductor and Output Capacitor Selection

To achieve better steady state and transient response, ISL9220,

ISL9220A typically uses a 10µH inductor. The peak-to-peak inductor

current ripple can be expressed in Equation 9:

In Equation 9, usually the typical values can be used but to have

a more conservative estimation, the inductance should consider

the value with worst case tolerance; and for switching frequency

page 3 can be used. A worst case for charge current ripple is

when battery voltage is half of the input voltage.

To select the inductor, its saturation current rating should be at

least higher than the sum of the maximum output current and

half of the delta calculated from Equation 9. Another more

conservative approach is to select the inductor with the current

rating higher than the peak current limit.

Another consideration is the inductor DC resistance since it

directly affects the efficiency of the converter. Ideally, the

inductor with the lower DC resistance should be considered to

achieve higher efficiency.

Inductor specifications could be different from different

manufacturers so please check with each manufacturer if

additional information is needed.

For the output capacitor, a ceramic capacitor can be used

because of the low ESR values, which helps to minimize the

output voltage ripple. A typical value of 10µF/10V ceramic

capacitor should be enough for most of the applications and the

capacitor should be X5R or X7R.

Board Layout Recommendations

The ISL9220, ISL9220A is a high frequency switching charger

and hence the PCB layout is a very important design practice to

ensure a satisfactory performance.

The power loop is composed of the output inductor L, the output

make the power loop as small as possible and the connecting

traces among them should be direct, short and wide; the same

practice should be applied to the connection of the VIN pin, the

The switching node of the converter, the SW pin, and the traces

connected to this node are very noisy, so keep the voltage

feedback trace and other noise sensitive traces away from these

noisy traces.

The input capacitor should be placed as close as possible to the

VIN pin. The ground of the input and output capacitors should be

connected as close as possible as well. In addition, a solid ground

plane is helpful for a good EMI performance.

The ISL9220, ISL9220A employs a thermal enhanced QFN

package with an exposed pad. In order to maximize the current

capability, it is very important that the exposed pad under the

package is properly soldered to the board and is connected to

other layers through thermal vias. More thermal vias and more

ΔI

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(EQ. 9)